Methods to increase response to postal and electronic questionnaires.

Background

Self‐administered questionnaires are widely used to collect data in epidemiological research ( Van Gelder 2010 ). When collecting information from large, geographically dispersed populations, a self‐administered questionnaire, delivered by post or electronically, is often the only financially viable option. Non‐response to questionnaires reduces the effective sample size and can introduce bias ( Armstrong 1995 ). This review updates our previous version, which was published in 2009 based on searches performed in Feb 2008 ( Edwards 2009 ).

Description of the methods being investigated

A previous review ( Yammarino 1991 ) suggested that repeated contacts (e.g. preliminary notification and follow‐up), appeals in letters, inclusion of a return envelope, types of postage, monetary incentives, and shorter questionnaires can increase response.

How these methods might work

Some methods (e.g. a shorter questionnaire or inclusion of a return envelope) might reduce the burden faced by individuals when completing and returning a questionnaire, leading to an increase in response. Other methods (e.g. incentives) might induce a sense of reciprocity in individuals such that they will complete and return a questionnaire in return for benefits received ( Molm 2010 ).

Why it is important to do this review

The identification of effective strategies to increase response to postal and electronic questionnaires will help to maintain power and reduce the risk of bias in study results, thus improving the quality of epidemiological research.

Objectives

To identify effective strategies to increase response to postal and electronic questionnaires.

Methods

Criteria for considering studies for this review

Types of studies

All unconfounded randomised trials of methods designed to increase response to postal or electronic questionnaires were eligible. A postal questionnaire was defined as a questionnaire that is delivered to a person’s home or work address by a distribution system. This includes questionnaires delivered by any postal service, including internal organisational mail and those hand‐delivered to a person’s address; It does not include questionnaires distributed at, for example, a shop or in a doctor’s office. An electronic questionnaire was defined as a questionnaire that is delivered electronically by email or by SMS and includes those administered online over the internet.

Types of data

Any population (e.g. patients or healthcare providers, and including any participants of non‐health studies) were eligible.

Types of methods

Any methods designed to increase response to postal or electronic questionnaires were eligible. Strategies requiring telephone contact as a follow‐up technique were included but those requiring home visits were not.

Types of outcome measures

Primary outcomes

Proportion of completed, or partially completed postal questionnaires returned after all mailings.

Proportion of participants completing or submitting the online questionnaire.

Secondary outcomes

Proportion of completed, or partially completed questionnaires returned after the first mailing.

Proportion of participants logging in or clicking the hyperlink to visit the online questionnaire.

Search methods for identification of studies

Electronic searches

We identified trials by searching 14 electronic bibliographic databases. We ran these searches in December 2021 and have agreed with Cochrane Methodology that the search should not be updated further after this time. This is because the very large number of reports identified in the December 2021 search and the stability of our overall conclusions means that updating our searches would be of much less relevance than it would be for Cochrane Reviews focusing on clinical questions.

Searching other resources

We handsearched two journals (Public Opinion Quarterly, from 1960 to 1998; American Journal of Epidemiology, from 1948 to 1999). We also searched the reference lists of all identified trials, the reference lists of relevant meta‐analyses, and contacted the authors of the included trials. Full details of the search strategies used for all review versions are illustrated in Appendix 1 .

Data collection and analysis

Selection of studies

Two authors independently examined the titles, abstracts and keywords of all records identified from the electronic searches. We obtained full‐text articles (where available) of all selected abstracts and used an eligibility form to determine final study selection. We resolved any disagreements through discussion.

Data extraction and management

Two authors independently extracted data from eligible reports using a standard pro forma, with disagreements resolved by a third author. We extracted data on the type of intervention evaluated, the numbers randomised to intervention or control groups, the quality of allocation concealment, the types of participants, and the materials and follow‐up methods used. Two outcomes were used for each method of delivery to estimate the effect of each intervention on the questionnaire response. For postal, the proportion of questionnaires returned after the first mailing, and the proportion returned after all follow‐up contacts were measured. For electronic, the proportion of participants logging‐in or clicking the hyperlink to visit the online questionnaire, and the proportion of participants completing or submitting the online questionnaire were measured. We excluded trials in which we could not confirm that random allocation had been used to allocate participants. For this 2023 update, we used the online screening and data extraction tool in Covidence and then exported the data from Covidence into a spreadsheet for entry into Review Manager 5 ( Review Manager 2020 ).

As per the original review and in all subsequent updates, we used the first author’s name with the publication year of the reference as the trial identifier. When more than one trial was reported in the paper, we identified these separately by adding letters a, b, c, etc. For example:

Allen 2016 reported two independent experiments, which we have included separately as Allen 2016 and Allen 2016a .

Roszkowski 1990 reported independent replications of the same trial in 14 different populations and we have reported them as Roszkowski 1990a ; Roszkowski 1990b ; Roszkowski 1990c ; Roszkowski 1990d ; Roszkowski 1990e ; Roszkowski 1990f ; Roszkowski 1990g ; Roszkowski 1990h ; Roszkowski 1990i ; Roszkowski 1990j ; Roszkowski 1990k ; Roszkowski 1990l ; Roszkowski 1990m ; Roszkowski 1990n .

Gibson 1999 randomised participants to different monetary incentives and reported the results separately for a sample of Medicaid participants ( Gibson 1999a ) and for a sample of Basic Health Plan participants ( Gibson 1999b ). All non‐respondents were randomised to a reminder sent using either Certified postal delivery or standard postal delivery ( Gibson 1999c ).

Assessment of risk of bias in included studies

In the original review version and in the prior update versions ( Edwards 2003 ; Edwards 2007 ; Edwards 2009 ), we focused on the integrity of allocation concealment and two authors independently scored methodological quality on the scale used by Schulz ( Schulz 1995 ) as shown below, assigning 'A' to best quality and 'C' to poorest quality:

A ‐ trials deemed to have taken adequate measures to conceal allocation (i.e. central randomisation; computer‐generated address labels; or other description that contained elements that would ensure concealment);

B ‐ trials in which the authors either did not report an allocation concealment approach at all or reported an approach that did not fall into one of the other categories;

C‐ trials in which concealment was inadequate (such as alternation or reference to case record numbers or to dates of birth).

Where the methods used to conceal allocation were not clearly reported, the study authors were contacted, if possible, for clarification. We then compared the scores allocated and resolved differences by discussion. For the current third update version, the risk of bias judgements from the original review and its subsequent updates were carried over ( Edwards 2003 ; Edwards 2007 ; Edwards 2009 ), and two authors used the Cochrane Collaboration’s tool for assessing the risk of bias ( Higgins 2011 ) to assess the risk of bias for each newly added study as 'high', 'low', or 'unclear' risk of bias for the seven domains below:

Sequence generation;

Allocation concealment;

Blinding of participants and personnel;

Blinding of outcome assessment;

Incomplete outcome data;

Selective reporting;

Other sources of bias.

We reported the results relating to allocation concealment in all the studies included in this update, and results relating to the other domains for the newly added studies only.

Measures of the effect of the methods

We classified and analysed methods under broad strategies to increase questionnaire response, for example: Incentives ‐ What are participants offered? (e.g. monetary incentive vs. no incentive, unconditional incentive vs. conditional incentive, incentive with first vs. subsequent mailing); Appearance ‐ How does the questionnaire look? (e.g. more personalised vs. less, teaser on envelope vs. none); Delivery ‐ How are the questionnaires received or returned? (e.g. stamped vs. franked outward envelope, certified/special delivery vs. regular outward mailing); Contact ‐ Methods and number of requests for participation (e.g. pre‐contact vs. no pre‐contact, follow‐up vs. no follow‐up); Content ‐ Nature and style of questions (e.g. sensitive questions vs. no/fewer/less sensitive questions asked, demographic items first vs. last, horizontal vs. vertical orientation of response options); Origin ‐ Who sent the questionnaire? (e.g., University sponsor/source vs. other, sent or signed by more vs. less senior/well‐known person); Communication ‐ What are participants told? (e.g. assurance of confidentiality vs. none, participants told completion time 10 mins vs. 30 mins); Length ‐ How long is the questionnaire? (e.g. shorter vs. longer questionnaire, double postcard vs. one page).

In trials with factorial designs, we classified methods under two or more strategies. When methods were evaluated at more than two levels (e.g. highly, moderately and slightly personalised questionnaires), we combined the upper levels, creating a dichotomy. For example, we compared response to the least personalised questionnaire with the combined response to the moderately and highly personalised questionnaires. Monetary incentives were defined as any incentive that could be used by participants as money (e.g. cash). Incentives such as a donation to charity, entrance into a lottery, or a gift (e.g. a pen) were classified as ’non‐monetary’ incentives.

For each included study, we calculated an odds ratio and its 95% confidence interval as the measure of the effect of the method to increase questionnaire response.

Unit of analysis issues

In the small minority of studies that had used a cluster‐randomised design, we did not adjust the results to allow for clustering, but we noted that these were at risk of ‘Other sources of bias’.

Dealing with missing data

We wrote to the authors of reports where required information was missing. See Data extraction and management .

Assessment of heterogeneity

We assessed heterogeneity amongst trial odds ratios using a Chi‐squared test at a 5% significance level, and the degree of inconsistency between trial results was quantified using the I 2 statistic ( Higgins 2003 ). The I 2 statistic measures the percentage of variation across studies, which is due to heterogeneity. We used the following categories for our interpretation of the I 2 statistic ( Higgins 2022 ):

0‐40% might not be important;

30‐60% moderate heterogeneity;

50‐90% substantial heterogeneity;

75‐100% considerable heterogeneity.

Assessment of reporting biases

We assessed evidence for small study bias (such as reporting bias) using Egger’s weighted regression method and Begg’s rank correlation test and funnel plots.

Data synthesis

For each of the broad strategies to increase questionnaire response, we estimated pooled odds ratios in Review Manager 2020 using a random‐effects model. We calculated 95% confidence intervals and two‐sided P values for each outcome.

Subgroup analysis and investigation of heterogeneity

As per our earlier review versions ( Edwards 2003 ; Edwards 2007 ; Edwards 2009 ), no subgroup analyses or meta‐regressions were planned/performed.

Sensitivity analysis

As per our earlier review versions ( Edwards 2003 ; Edwards 2007 ; Edwards 2009 ), no sensitivity analyses were planned/performed.

Results

Description of studies

Results of the search

For this update: of 92,453 identified abstracts and titles, we removed duplicates and screened 68,193 records/references for eligibility for inclusion. We selected 395 potentially eligible references for independent eligibility assessment of the full‐text reports. After screening full‐text reports, 114 were excluded (reasons for exclusion are summarised in Characteristics of excluded studies ). Of the remaining 281 records, 32 were subsequently found to be duplicates, and 26 required further contact with the authors and are listed in Characteristics of studies awaiting classification (also lists the 23 studies awaiting classification from the previous update, Edwards 2009 ).

Therefore, our updated search identified a total of 223 full‐text records reporting on 245 new trials, bringing the total number of included trials to 758 (513 included in the previous update, Edwards 2009 ) ( Characteristics of included studies ).

Included studies

Postal questionnaires

We have identified a total of 670 eligible trials that evaluated over 100 different strategies for increasing response to postal questionnaires. See Characteristics of included studies for further details.

Electronic questionnaires

We have identified a total of 88 eligible trials that evaluated over 30 different strategies for increasing response to electronic questionnaires. See Characteristics of included studies for further details.

Excluded studies

From the latest updated search, we excluded 114 studies: 73 were not a randomised trial, 34 did not use a postal questionnaire, 6 were confounded trials, and 1 was a trial protocol. See Characteristics of excluded studies for further details (also lists the reasons for excluding 87 studies from the previous update, Edwards 2009 ).

Risk of bias in included studies

See Figure 1 for our risk of bias assessments on the domain 'allocation concealment' in all the included studies in this update, and results relating to the other domains for the newly added studies only.

Allocation

Of the 513 previously identified trials, allocation concealment was classified as C (inadequate) in 76 trials, A (adequate) in 83 trials, and as B (unclear) in the remaining trials. Of the 245 newly added trials, we judged five trials to be at high risk of bias, 112 trials to be at low risk of bias, and there was unclear risk of bias in the remaining trials.

For sequence generation, of the 245 newly added trials, we judged five trials to be at high risk of bias, 110 trials to be at low risk of bias, and there was unclear risk of bias in the remaining trials.

Blinding

Of the 245 newly added trials, participants were not blinded to the intervention in 131 trials. No outcomes were assessed on the participants in any of the included trials (only the counts of responses in the experimental and control groups were reported), and so blinding of outcome assessors was not a risk of bias in any of the newly added trials.

Incomplete outcome data

Of the 245 newly added trials, exclusions were not reported in 34 trials. The remaining trials were at low risk of bias due to follow‐up and exclusions.

Selective reporting

Of the 245 newly added trials, 235 trials reported outcomes in full.

Other potential sources of bias

Of the 245 newly added trials, seven were judged to be at a ‘high’ risk of bias due to results not being adjusted for clustering.

Effect of methods

Table 1 presents a summary of the main findings of this review update.

Incentives ‐ What are participants offered? (Strategies 1‐22)

Postal questionnaires

One hundred and eleven trials (226,209 participants) evaluated the effect of a monetary incentive on questionnaire response. The odds of response were almost doubled using monetary incentives (odds ratio (OR) 1.86; 95% confidence interval (CI) 1.73 to 1.99). There was, however, considerable heterogeneity amongst the trial results (I 2 = 85%) ( Analysis 1.2 ). Fifty trials (137,457 participants) evaluated the effect of a larger rather than a smaller monetary incentive on questionnaire response. The odds of response were a quarter higher when a larger monetary incentive was used (OR 1.24; 95% CI 1.15 to 1.33). There was considerable heterogeneity amongst the trial results (I 2 = 82%) ( Analysis 2.2 ). Seventeen trials (28,212 participants) evaluated the effect of offering a monetary rather than a non‐monetary incentive on questionnaire response. The odds of response were increased by over half when a monetary incentive rather than a non‐monetary incentive was used (OR 95% CI 1.67; 95% CI 1.47 to 1.90). There was considerable heterogeneity amongst the trial results (I 2 = 75%) ( Analysis 3.2 ).

One hundred and forty‐six trials (277,802 participants) evaluated the effect of a non‐monetary incentive (e.g. key‐ring, lottery participation, donation to charity, offer of study results, candy, etc.) on questionnaire response. The odds of response were increased by over a tenth when a non‐monetary incentive was used (OR 1.16; 95% CI 1.11 to 1.21). There was considerable heterogeneity amongst the results of non‐monetary incentive trials (I 2 = 80%) ( Analysis 4.2 ). Eleven trials (18,688 participants) evaluated the effect of a larger rather than a smaller non‐monetary incentive on questionnaire response. There was a possibility that using a larger non‐monetary incentive may increase the odds of response (OR 1.15; 95% CI 1.00 to 1.33; P = 0.05). However, there was considerable heterogeneity amongst the trial results (I 2 = 77%) ( Analysis 5.2 ).

Thirty‐five trials (48,850 participants) evaluated the timing of incentives on questionnaire response. The odds of response increased by more than a half when incentives were given with questionnaires (i.e. unconditional) rather than when only given after participants had returned their questionnaires (i.e. conditional on response) (OR 1.53; 95% CI 1.35 to 1.74). There was considerable heterogeneity amongst the trial results (I 2 = 89%) ( Analysis 6.2 ). Four trials (8942 participants) evaluated the effect of offering an incentive with the first rather than a subsequent mailing. The odds of response were increased by over a tenth when the incentive was offered with the first mailing (OR 1.14; 95% CI 1.03 to 1.26). There was no evidence of heterogeneity amongst the trial results (I 2 = 0%) ( Analysis 7.2 ). Thirteen trials (20,052 participants) evaluated the effect of offering survey results as an incentive. There was no evidence for an effect on response of offering the study results (OR 0.91; 95% CI 0.78 to 1.05). There was considerable heterogeneity amongst the trial results (I 2 = 76%) ( Analysis 8.2 ).

Fourteen trials (46,096 participants) evaluated the effect on questionnaire response of sending a pen with the questionnaire compared to sending the questionnaire without a pen. The odds of response were increased by a third when a pen was included (OR 1.32; 95% CI 1.14 to 1.53). There was considerable heterogeneity amongst the trial results (I 2 = 89%) ( Analysis 9.2 ). A single trial (6167 participants) evaluated the effect of sending the questionnaire with a more expensive pen compared to sending the questionnaire with a cheaper pen. There was no evidence for an effect on response of sending a questionnaire with a more expensive pen (OR 1.03; 95% CI 0.81 to 1.31) ( Analysis 10.2 ). The same trial (6167 participants) evaluated the effect of sending the questionnaire with a pen in a box compared to sending the questionnaire with an unboxed pen. The odds of response were increased by a tenth when the pen was in a box (OR 1.10; 95% CI 1.00 to 1.22) ( Analysis 11.2 ). A single trial (2342 participants) evaluated the effect of sending a monetary incentive with the follow‐up mailing compared to no incentive with the follow‐up. There was no evidence for an effect on response of sending a monetary incentive with the follow‐up mailing (OR 0.97; 95% CI 0.82 to 1.16) ( Analysis 12.2 ). A single trial (444 participants) evaluated the effect of sending the questionnaire with non‐monetary incentives compared to sending the questionnaire with the promise of making a charitable donation. The odds of response were nearly one half greater with a non‐monetary incentive than with a donation to charity (OR 1.44; 95% CI 0.98 to 2.12) ( Analysis 13.1 ). A single trial (531 participants) evaluated the effect of sending the questionnaire with a cheque incentive that required the participant to give their social security number ID to cash it, compared to sending the questionnaire with a cheque incentive that did not require a social security number ID. There was no evidence for an effect on response when participants were required to give their social security number ID (OR 0.75; 95% CI 0.41 to 1.37) ( Analysis 14.1 ). Eleven trials (19,981 participants) evaluated the effect on questionnaire response via including a study brochure with the questionnaire compared to no brochure. There was no evidence for an effect on response of including a study brochure (OR 0.97; 95% CI 0.83 to 1.13). There was moderate heterogeneity between the trial results (I 2 = 64%) ( Analysis 15.3 ). A single trial (303 participants) evaluated the effect of sending a cheque incentive compared to sending the questionnaire with a cashcard (i.e. a reloadable debit card). The odds of response were greater with a cheque than with a cashcard (OR 1.81; 95% CI 1.15 to 2.86) ( Analysis 16.2 ). A single trial (2856 participants) evaluated the effect of sending a monetary incentive comprising multiple banknotes compared to a single note. There was no evidence for an effect on response with multiple banknotes compared to a single note (OR 1.08; 95% CI 0.94 to 1.26) ( Analysis 17.2 ).

Electronic questionnaires

Five trials (6446 participants) evaluated the effect of a monetary incentive on electronic questionnaire response. The odds of response were almost doubled using monetary incentives (OR 1.88; 95% CI 1.31 to 2.71). There was considerable heterogeneity between the trial results (I 2 = 79%) ( Analysis 1.4 ). Three trials (3614 participants) evaluated the effect of a monetary rather than a non‐monetary incentive on e‑questionnaire response. There was no evidence for an effect on response of using a monetary rather than a non‐monetary incentive (OR 0.89; 95% CI 0.63 to 1.26). There was considerable heterogeneity between the trial results (I 2 = 81%) ( Analysis 3.4 ). Sixteen trials (38,901 participants) evaluated the effect of a non‐monetary incentive (e.g. Amazon gift cards, lottery participation, personal digital assistant, early grade feedback, etc.) on e‐questionnaire response. The odds of response were almost doubled when a non‐monetary incentive was used (OR 1.60; 95% CI 1.25 to 2.05). There was considerable heterogeneity amongst the trial results (I 2 = 93%) ( Analysis 4.4 ). Ten trials (37,382 participants) evaluated the effect of a larger rather than a smaller non‐monetary incentive on e‐questionnaire response. There was no evidence for an effect on response of using a larger non‐monetary incentive (OR 1.07; 95% CI 0.87 to 1.32). There was considerable heterogeneity amongst the trial results (I 2 = 89%) ( Analysis 5.4 ).

Three trials (1401 participants) evaluated the timing of incentives on e‐questionnaire response. There was no evidence for an effect on response when incentives were given with e‐questionnaires (i.e. unconditional) rather than only given after participants had submitted their e‐questionnaire (i.e. conditional on response) (OR 1.08; 95% CI 0.77 to 1.50) ( Analysis 6.4 ). Two trials (2884 participants) evaluated the effect on e‐questionnaire response of offering survey results as an incentive. The odds of response increased by over a third when an offer of results was used (OR 1.36; 95% CI 1.16 to 1.59) ( Analysis 8.3 ).

One trial (2233 participants) evaluated the effect of immediate notification of lottery results compared to delayed notification on e‐questionnaire response. The odds of response were increased by almost half when lottery results were immediately notified (OR 1.37; 95% CI 1.13 to 1.65) ( Analysis 20.1 ). Two trials (4721 participants) evaluated the effect of higher denominations of currencies in a monetary lottery compared to lower denominations on e‐questionnaire response. There was no evidence for an effect on response of offering higher denominations in a monetary lottery (OR 1.00; 95% CI 0.87 to 1.14) ( Analysis 18.1 ). One trial (1061 participants) evaluated the combined effect of conditional and unconditional incentives on e‐questionnaire response compared to conditional incentives alone. There was no evidence for an effect on response of using the combined incentives (OR 1.19; 95% CI 0.92 to 1.54) ( Analysis 19.1 ). Another trial (3000 participants) evaluated the combined effect of conditional and unconditional incentives on e‐questionnaire response compared to unconditional incentives alone. This trial found evidence that response was increased using the combined incentives (OR 1.23; 95% CI 1.06 to 1.44) ( Analysis 21.4 ). A single trial (130 participants) evaluated the effect on response to a smart‐phone daily diary app that included a game that gave in‐game rewards when a daily diary was completed. There was no evidence that the inclusion of the game increased response (OR 0.51; 95% CI 0.19 to 1.40) ( Analysis 22.2 )

Appearance ‐ How do the questionnaires look? (Strategies 23‐60)

Postal questionnaires

Seventy‐four trials (97,674 participants) evaluated the effect on questionnaire response of making questionnaire materials more personal, such as signing letters by hand. The odds of response were increased by more than a tenth with a more personalised approach to participants (OR 1.15; 95% CI 1.09 to 1.21). There was, however, considerable heterogeneity amongst the results of these trials (I 2 = 57%) ( Analysis 23.2 ). Fourteen trials (15,006 participants) evaluated the effect of cover letters bearing a handwritten signature compared to those that are typed or scanned or printed. The odds of response increased by a quarter using handwritten signatures (OR 1.24; 95% CI 1.08 to 1.41) ( Analysis 24.2 ). Nine trials (6030 participants) evaluated the effect of handwritten address labels compared to computer‐printed labels. The odds of response increased by a quarter when using the handwritten labelled questionnaire (OR 1.23; 95% CI 1.09 to 1.37) ( Analysis 25.2 ). Three trials (1364 participants) evaluated the presence of a signature within the questionnaire. There was some evidence for an effect on response of using a signature within the questionnaire (OR 1.35; 95% CI 1.04 to 1.76) ( Analysis 26.2 ).

Ten trials (5297 participants) evaluated the effect of including an identifying feature, such as a participant’s name or identity number, on questionnaire response. There was no evidence for an effect on response of using an identifying feature (OR 1.03; 95% CI 0.81 to 1.32). There was considerable heterogeneity between the trial results (I 2 = 71%) ( Analysis 27.2 ). One trial (741 participants) evaluated the effect on response of an identifying number on the returned questionnaire compared with another identifier. There was no evidence for an effect on response of using an identifying number (OR 1.00; 95% CI 0.68 to 1.46) ( Analysis 28.2 ).

Fifteen trials (43,754 participants) evaluated the effect on response of using questionnaires printed on coloured paper. There was no evidence for an effect on response of using a coloured questionnaire (OR 1.03; 95% CI 0.98 to 1.09) ( Analysis 29.2 ). Three trials (7040 participants) evaluated the effect of using coloured ink, compared with black or blue ink, on questionnaire response. There was no evidence for an effect on response of using coloured ink (OR 1.16; 95% CI 0.95 to 1.42). There was moderate heterogeneity between the trial results (I 2 = 67%) ( Analysis 30.2 ). Two trials (2356 participants) evaluated the effect of a coloured letterhead compared to a black and white letterhead. There was no evidence for an effect on response of using a coloured letterhead (OR 1.08; 95% CI 0.91 to 1.28) ( Analysis 31.2 ). A single trial (320 participants) evaluated the effect of an illustration on the cover of the questionnaire largely in black, versus largely in white. The odds of response increased by more than a half when using an illustration on the cover of the questionnaire that was largely in black (OR 1.62; 95% CI 1.04 to 2.53) ( Analysis 32.1 ). Three trials (5681 participants) evaluated the effect on response of using a booklet compared to stapled pages. There was no evidence for an effect on response of using a booklet (OR 1.10; 95% CI 0.99 to 1.23) ( Analysis 33.2 ). Two trials (2145 participants) evaluated the effect of the paper size of the questionnaire on response. There was no evidence for an effect on response of using a large paper size (OR 0.88; 95% CI 0.56 to 1.39) ( Analysis 34.2 ). A single trial (176 participants) evaluated the effect on questionnaire response of printing the questionnaire using dot‐matrix compared to a letter‐quality print. There was no evidence for an effect of response of using the dot‐matrix print (OR 1.15; 95% CI 0.63 to 2.10) ( Analysis 35.1 ).

Three trials (3372 participants) evaluated the effect of the questionnaire being printed on a high quality or thicker paper, compared to standard quality or thin paper. There was no evidence for an effect on response of using a high quality or a thicker paper (OR 0.83; 95% CI 0.68 to 1.02) ( Analysis 36.1 ). Five trials (9383 participants) evaluated the effect of using a single‐sided questionnaire compared to a double‐sided questionnaire. The odds of response increased by a tenth when a single‐sided questionnaire was used (OR 1.13; 95% CI 1.02 to 1.25) ( Analysis 37.2 ). One trial (650 participants) evaluated the effect on response of using a larger font compared to a smaller font. There was no evidence for an effect on response of using larger fonts (OR 1.26; 95% CI 0.87 to 1.82) ( Analysis 38.1 ). A single trial (1000 participants) compared the presence of a study logo on several items in the mailing package to its presence in the questionnaire only. There was no evidence for an effect on response of using the study logo on several items in the mailing package (OR 0.92; 95% CI 0.72 to 1.18) ( Analysis 39.1 ). Five trials (3956 participants) evaluated the effect of the presence of a picture in the questionnaire. There was no evidence for an effect on response of using a picture (OR 1.03; 95% CI 0.70 to 1.51) ( Analysis 40.2 ). One trial (280 participants) evaluated the effect on response of including a cartoon in the questionnaire. There was no evidence for an effect on response of including a cartoon (OR 1.00; 95% CI 0.62 to 1.62) ( Analysis 42.1 ). Two trials (2904 participants) evaluated the effect on response of questionnaires having a more professional design compared with a standard design. There was no evidence for an effect on response of questionnaires having a more professional design (OR 1.00; 95% CI 0.58 to 1.72). There was considerable heterogeneity between the trial results (I 2 = 88%) ( Analysis 43.2 ).

Two trials (901 participants) evaluated the effect on questionnaire response of sending personalised SMS reminders to non‐respondents compared with standard SMS reminders. There was some evidence that the odds of response were increased with personalised SMS reminders (OR 1.53; 95% CI 0.97 to 2.43) ( Analysis 44.2 ). A single trial (231 participants) evaluated the effect on response of using "Action Required" as the subject line of an email reminder compared with “Questionnaire reminder” as the subject. There was no evidence for an effect on response of using "Action Required" as the subject line (OR 0.61; 95% CI 0.23 to 1.63) ( Analysis 45.2 ). Two trials (3895 participants) evaluated the effect on response of including a message about an incentive on the envelope compared with none. There was no evidence for an effect on response by including a message (OR 0.91; 95% CI 0.80 to 1.04) ( Analysis 46.2 ). A single trial (1569 participants) evaluated the effect on response of a health message on the envelope compared with a monetary incentive message. There was no evidence that response differed between the health or the monetary incentive messages (OR 1.05; 95% CI 0.86 to 1.29) ( Analysis 47.2 ). Five trials (23,621 participants) evaluated the effect of including a ‘teaser’ on the envelope. There was no evidence for an effect on response when a teaser was used (OR 1.08; 95% CI 0.95 to 1.22) There was moderate heterogeneity amongst the trial results (I 2 = 37%) ( Analysis 48.2 ). Two trials (1678 participants) evaluated the effect of using a more readable/concise/info‐mapped letter on response. There was no evidence for an effect on response of using a more readable/concise/info‐mapped letter (OR 0.88; 95% CI 0.72 to 1.09) ( Analysis 49.2 ). A single trial (517 participants) evaluated the effect on response of a study logo sticker on the envelope compared with no sticker. There was no evidence that response was increased with the sticker (OR 1.06; 95% CI 0.75 to 1.49) ( Analysis 50.1 ).

Electronic

Twelve trials (48,910 participants) evaluated the effect on e‐questionnaire response by addressing the salutations in the cover letters accompanying the questionnaires personally, or by giving a touch of personalisation to the cover letters. The odds of response were increased by about a quarter when a personalised approach was adopted (OR 1.24; 95% CI 1.17 to 1.32). There was moderate heterogeneity between trial results (I 2 = 41%) ( Analysis 23.4 ). Two trials (720 participants) evaluated the effect of the presence of a picture in the email. The odds of response tripled when a picture was sent in the email (OR 3.05; 95% CI 1.84 to 5.06) ( Analysis 40.3 ). The same trials (520 participants) evaluated the effect of response when a more attractive picture was used compared to a less attractive picture. There was little evidence for an effect on response of using a more attractive picture (OR 3.44; 95% CI 0.72 to 16.49) ( Analysis 41.1 ).

Two trials (6152 participants) evaluated the presence of a topic in the subject line of the email compared to a blank subject line. There was no evidence for an effect on response of using a topic in the subject line (OR 0.84; 95% CI 0.71 to 1.01) ( Analysis 51.2 ). Two trials (3845 participants) evaluated the presence of “Survey” as the subject line compared to a blank subject line. The odds of response decreased by a fifth when “Survey” was mentioned in the subject line (OR 0.81; 95% CI 0.67 to 0.97) ( Analysis 52.2 ).

One trial (6090 participants) evaluated the effect of sending emails in text‐file format compared to HTML. There was no evidence for an effect on response of using text file format (OR 1.00; 95% CI 0.84 to 1.19) ( Analysis 53.1 ). The same trial (6090 participants) evaluated the presence of using a white background in the email compared to a black background. The odds of response increased by over a quarter when a white background was used (OR 1.31; 95% CI 1.10 to 1.56) ( Analysis 54.1 ). The same trial (6090 participants) also evaluated the effect of including a header compared to no header in the email. There was no evidence for an effect on response of using a header (OR 1.13; 95% CI 0.90 to 1.41) ( Analysis 55.1 ). The same trial (5075 participants) also evaluated the effect of a simple header compared to a complex header. The odds of response increased by almost a quarter when a simple header was used (OR 1.23; 95% CI 1.03 to 1.48) ( Analysis 56.1 ).

One trial (5413 participants) evaluated the effect of textual presentation of response categories compared to visual presentation of response categories. The odds of response increased by almost a fifth when textual presentation was used (OR 1.19; 95% CI 1.05 to 1.36) ( Analysis 57.1 ). A single trial (517 participants) evaluated the effect on response of formatting a web survey as a single scrollable page compared with multiple pages. There was no evidence for an effect on response of using a single scrollable page (OR 0.93; 95% CI 0.66 to 1.32) ( Analysis 58.1 ). Two trials (3676 participants) evaluated the effect on e‐questionnaire response of an email subject line that emphasised an incentive compared with no such emphasis on the subject. There was no evidence for an effect on response when the email subject emphasised an incentive (OR 2.19; 95% CI 0.58 to 8.27). There was considerable heterogeneity between the trial results (I 2 = 97%) ( Analysis 59.2 ). A single trial (2963 participants) evaluated the effect on e‐questionnaire response of an email reminder including humour compared to a standard email. There was no evidence for an effect on response when including humour (OR 1.17; 95% CI 0.99 to 1.38) ( Analysis 60.1 ).

Delivery ‐ How are the questionnaires received or returned? (Strategies 61‐93)

Postal

Six trials (13,964 participants) evaluated the effect on questionnaire response of using stamps on outgoing envelopes compared to franked envelopes. There was no evidence for an effect on response of using stamps on outgoing envelopes (OR 0.95; 95% CI 0.88 to 1.03) ( Analysis 61.2 ). Two trials (8300 participants) evaluated the effect on questionnaire response of using first class compared to other classes of postage. The odds of response were increased by over one‐tenth using first‐class postage (OR 1.11; 95% CI 1.02 to 1.21) ( Analysis 62.2 ).

Five trials (5461 participants) evaluated the effect on questionnaire response of using commemorative stamps rather than standard stamps on return envelopes. There was no evidence for an effect on response of using commemorative stamps (OR 0.92; 95% CI 0.81 to 1.06) ( Analysis 63.2 ). Nineteen trials (30,492 participants) evaluated the effect on questionnaire response of using a special delivery service (e.g. recorded, registered, or certified delivery), rather than standard delivery. The odds of response increased by more than half when special delivery was used (OR 1.68; 95% CI 1.36 to 2.08). Results were considerably heterogeneous (I 2 = 87%) ( Analysis 64.2 ). Twenty‐eight trials (55,550 participants) evaluated the effect on questionnaire response of using a stamped return envelope compared to a pre‐paid business or franked reply envelope. The odds of response increased by a quarter when stamps were used (OR 1.23; 95% CI 1.13 to 1.33). There was moderate heterogeneity between the trial results (I 2 = 69%) ( Analysis 65.2 ). One trial (205 participants) evaluated the effect of using priority stamps on return envelopes compared to using a first‐class stamp. The odds of response decreased by more than a half when priority stamps were used (OR 0.26; 95% CI 0.14 to 0.46) ( Analysis 66.1 ). One trial (800 participants) evaluated the effect of using a first‐class stamp on return envelopes compared to a second‐class stamp. There was no evidence for an effect on response of using a first‐class stamp on the return envelope (OR 0.91; 95% CI 0.69 to 1.21) ( Analysis 67.1 ).

A single trial (510 participants) evaluated the use of multiple stamps on return envelopes compared to a single stamp. The odds of response increased by almost half when multiple stamps were used (OR 1.44; 95% CI 1.01 to 2.04) ( Analysis 68.1 ). Four trials (4094 participants) evaluated the effect on questionnaire response of providing any sort of pre‐paid return envelope rather than none. There was no evidence for an effect on response of including pre‐paid envelopes (OR 1.09; 95% CI 0.71 to 1.68). There was considerable heterogeneity amongst the trial results (I 2 = 87%) ( Analysis 69.2 ). A single trial (147 participants) evaluated the effect of including a stamped addressed return envelope compared to only including an address label. This trial provided no evidence for an effect on response of using a stamped addressed return envelope (OR 0.86; 95% CI 0.45 to 1.65) ( Analysis 70.1 ).

Two trials (1140 participants) evaluated the effect on response of sending questionnaires to the participant’s work address rather than to their home address. There was no evidence for an effect on response of sending questionnaires to work addresses (OR 1.16; 95% CI 0.89 to 1.52) ( Analysis 71.2 ). Two trials (11,781 participants) evaluated the effect of using a window envelope on questionnaire response. There was no evidence for an effect on response of using window envelopes (OR 0.96; 95% CI 0.61 to 1.49). There was considerable heterogeneity between the trial results (I 2 = 75%) ( Analysis 72.2 ). A single trial (1200 participants) evaluated the effect on questionnaire response of sending the questionnaire in a larger envelope compared to a standard or smaller envelope. There was no evidence for an effect on response of using larger envelopes (OR 0.93; 95% CI 0.74 to 1.17) ( Analysis 73.1 ).

Six trials (9756 participants) evaluated the effect on questionnaire response of using brown envelopes compared to white. There was no evidence for an effect on response of using a brown envelope (OR 1.25; 95% CI 0.86 to 1.80). There was considerable heterogeneity between the trial results (I 2 = 92%) ( Analysis 181.2 ). Two trials (1843 participants) evaluated the effect of questionnaires being mailed on Monday compared to being sent on Friday. There was no evidence for an effect on response of sending the questionnaire on Monday (OR 0.84; 95% CI 0.70 to 1.01) ( Analysis 74.2 ). Two trials (2324 participants) evaluated the effect on response of questionnaires being sent one to five weeks after discharge from hospital, compared to being sent after 9 to 14 weeks. There was little evidence for an effect on response of questionnaires being sent sooner after discharge from hospital (OR 2.26; 95% CI 0.69 to 7.37). There was considerable heterogeneity between the trial results (I 2 = 83%) ( Analysis 76.1 ).

One trial (460 participants) evaluated the effect of a questionnaire being received on a Monday, compared to being received on a Friday. There was no evidence for an effect on response of questionnaires being received on a Monday (OR 1.00; 95% CI 0.64 to 1.56) ( Analysis 75.1 ). One trial (1600 participants) evaluated the effect on response of using a padded envelope compared to a priority mail envelope. There was no evidence for an effect on response of using a padded envelope (OR 0.88; 95% CI 0.72 to 1.07) ( Analysis 77.1 ).

A small trial (135 participants) evaluated the effect on response of the questionnaire being hand‐delivered by a person known to the recipient compared to standard postal delivery. The odds of response were more than doubled when the questionnaire was hand‐delivered by a known person (OR 2.60; 95% CI 1.29 to 5.23) ( Analysis 78.1 ). Two trials (937 participants) evaluated the effect on questionnaire response of hand delivery compared to postal delivery. There was no evidence overall that response was increased using hand delivery (OR 1.44; 95% CI 0.50 to 4.15). There was considerable heterogeneity amongst the trial results (I 2 = 88%) ( Analysis 79.1 ). One trial (199 participants) evaluated the effect on response of sending a postal questionnaire compared with sending it by fax. The odds of response were almost halved when sending by fax (OR 0.58; 95% CI 0.29 to 1.14) ( Analysis 80.2 ).

Electronic

Twenty‐seven trials (66,118 participants) evaluated the effect on response of sending a postal questionnaire compared with sending an e‐questionnaire. The odds of response were almost doubled using a postal questionnaire (OR 1.76; 95% CI 1.34 to 2.32). . There was, however, considerable heterogeneity between the trial results (I 2 = 98%) ( Analysis 81.2 ). Eight trials (20,909 participants) evaluated the effect of providing a choice of response modes (i.e. postal with optional electronic response) compared to postal only. There was no evidence for an effect on response by providing an optional electronic response mode (OR 0.94; 95% CI 0.86 to 1.02). There was moderate heterogeneity amongst the trial results (I 2 = 51%) ( Analysis 82.2 ).

Four trials (2958 participants) evaluated the effect on response of sending a postal questionnaire first with electronic follow‐up compared to an e‐questionnaire first with postal follow‐up. There was no evidence for an effect on response of sending a postal questionnaire first (OR 1.19; 95% CI 0.76 to 1.87). There was considerable heterogeneity between the trial results (I 2 = 85%) ( Analysis 83.2 ). Ten trials (39,523 participants) evaluated the effect on response of providing a choice of response modes (electronic or postal response) compared to electronic only. Response was increased when providing a choice of response modes (electronic or postal response) compared to electronic only (OR 1.63; 95% CI 1.18 to 2.26). There was considerable heterogeneity between the trial results (I 2 = 97%) ( Analysis 84.2 ). A single trial (6188 participants) evaluated the effect on response of asking participants to request their desired type of questionnaire compared to offering a choice of a postal or an e‐questionnaire immediately. The odds of response were one‐half greater when offering the choice of postal or an e‐questionnaire immediately (OR 1.59; 95% CI 1.43 to 1.77) ( Analysis 85.2 ).

A single trial (2774 participants) evaluated the effect on response of administering the e‐questionnaire by computer compared to by smartphone. The odds of response were increased when using a computer rather than a smartphone (OR 1.62; 95% CI 1.36 to 1.94) ( Analysis 86.2 ). A single trial (620 participants) evaluated the effect on response of administering the questionnaire by smartphone and Web, compared to by post with email follow‐up contacts. There was no evidence for an effect on response of administering the questionnaire by smartphone and Web (OR 1.02; 95% CI 0.50 to 2.08) ( Analysis 87.2 ). One trial (195 participants) evaluated the effect on response of sending an e‐questionnaire compared with sending it by fax. The odds of response were almost four times greater with an e‐questionnaire than with a fax (OR 3.87; 95% CI 2.0 to 7.49) ( Analysis 88.2 ).

A single trial (382 participants) evaluated the effect on response of administering the questionnaire by SMS compared to by post. There was no evidence for an effect on response of administering the questionnaire by SMS (OR 1.19; 95% CI 0.60 to 2.32) ( Analysis 89.2 ). One trial (1943 participants) evaluated the effect of an e‐questionnaire being received on a Monday or Tuesday, compared to being received on a Friday. There was no evidence for an effect on response of e‐questionnaires being received on a Monday or Tuesday (OR 0.96; 95% CI 0.66 to 1.40) ( Analysis 75.3 ). A single trial (21,473 participants) evaluated the effect on response to a Web survey of varying the days on which invitation emails and reminders were sent. The odds of response were greater when fixing the days on which invitation emails and reminders are sent (OR 1.08; 95% CI 1.03 to 1.14) ( Analysis 90.2 ). The same trial evaluated the effect on response to a Web survey using a model to predict the best day on which to send invitation emails and reminders. The odds of response were greater when fixing the days on which invitation emails and reminders were sent (OR 1.05; 95% CI 1.00 to 1.11) ( Analysis 91.2 ).

One trial (1999 participants) evaluated the effect on response of sending a postal follow‐up to an e‐questionnaire compared with follow‐up using interactive voice response. The odds of response were over three‐quarters greater with postal follow‐up (OR 1.77; 95% CI 1.48 to 2.11) ( Analysis 92.2 ). One trial (353 participants) evaluated the effect on response of administering the questionnaire by SMS compared to by Web. There was no evidence for an effect on response of administering the questionnaire by SMS (OR 0.68; 95% CI 0.31 to 1.49) ( Analysis 93.2 ).

Contact ‐ Methods and number of requests for participation (Strategies 94‐121)

Postal

Fifty‐nine trials (89,146 participants) evaluated the effect on response of contacting participants before sending questionnaires. The odds of response were increased by a third when participants were pre‐notified (OR 1.36; 95% CI 1.23 to 1.51). There was considerable heterogeneity amongst the trial results (I 2 = 87%) ( Analysis 94.2 ). Seven trials (3322 participants) evaluated the effect on response of pre‐notification by telephone compared to by post. There was no evidence for an effect on response when participants were pre‐contacted by telephone instead of by post (OR 1.18; 95% CI 0.77 to 1.80). There was considerable heterogeneity amongst the trial results (I 2 = 85%) ( Analysis 95.2 ). Twenty‐four trials (53,555 participants) evaluated the effect on questionnaire response of follow‐up contact (e.g. repeat mailings or telephone calls) with participants who did not respond to the initial questionnaire. The odds of response increased by more than a quarter when follow‐up contact was used (OR 1.33; 95% CI 1.18 to 1.49). There was considerable heterogeneity amongst the results (I 2 = 75%) and both Begg’s and Egger’s tests indicated evidence of selection bias ( Analysis 96.2 ).

Thirteen trials (11,456 participants) evaluated the effect on response of providing participants with another copy of the questionnaire during postal follow‐up. The odds of response were increased by nearly a half when questionnaires were included during postal follow‐up (OR 1.41; 95% CI 1.13 to 1.77). There was considerable heterogeneity amongst these results (I 2 = 82%) ( Analysis 97.2 ). Eight trials (4057 participants) evaluated the effect on questionnaire response of using telephone rather than postal follow‐up. There was no evidence for an effect on response of using telephone follow‐up (OR 1.02; 95% CI 0.76 to1.38). There was moderate heterogeneity amongst the trial results (I 2 = 66%) ( Analysis 98.2 ).

Four trials (15,143 participants) evaluated the effect on response of a telephone reminder compared to no reminder. There was good evidence for an effect on response of using a telephone reminder (OR 1.96; 95% CI 1.03 to 3.74). There was considerable heterogeneity amongst the trial results (I 2 = 90%) ( Analysis 99.2 ). Six trials (7520 participants) evaluated the effect on questionnaire response of using a higher frequency follow‐up interval compared to a lower frequency follow‐up interval. The odds of response were increased by over one‐tenth using a higher frequency follow‐up interval (OR 1.13; 95% CI 1.02 to 1.25) ( Analysis 100.2 ). One trial (780 participants) evaluated the effect on response of contacting participants by letter before sending questionnaires compared to pre‐contact by postcard. There was no evidence for an effect on response when participants were pre‐contacted by postcard instead of by letter (OR 0.98; 95% CI 0.74 to 1.30) ( Analysis 101.2 ).

One trial (581 participants) evaluated the effect on response of contacting participants by letter before sending questionnaires compared to pre‐contact by email. There was no evidence for an effect on response when participants were pre‐contacted by letter instead of by email (OR 1.25; 95% CI 0.83 to 1.88) ( Analysis 102.2 ). One trial (930 participants) evaluated the effect on response of contacting participants by fax before sending questionnaires compared to pre‐contact by post. There was no evidence for an effect on response when participants were pre‐contacted by fax instead of by post (OR 0.92; 95% CI 0.71 to 1.20) ( Analysis 103.2 ). Two trials (582 participants) evaluated the effect on questionnaire response of follow‐up contact with participants by SMS or email, compared with no reminders. There was no evidence for an effect on response when electronic reminders were used (OR 1.80; 95% CI 0.88 to 3.68). There was moderate heterogeneity between the trial results (I 2 = 34%) ( Analysis 104.2 ).

Two trials (3824 participants) evaluated the effect on response of push‐to‐web (i.e. initial requests sent by post and participants are asked to complete questionnaires over the Web) compared to mail‐push (initial mail contact with reminders of the paper questionnaire and an option to complete the survey online). There was no evidence for an effect on response with mail‐push (OR 1.10; 95% CI 0.87 to 1.39). There was moderate heterogeneity between the trial results (I 2 = 60%) ( Analysis 105.2 ). Four trials (3998 participants) evaluated the effect on response of sending a mixed‐mode reminder compared to a postal reminder. There was no evidence for an effect on response when non‐respondents were sent a mixed‐mode reminder (OR 1.13; 95% CI 0.83 to 1.52). There was moderate heterogeneity amongst the trial results (I 2 = 52%) ( Analysis 106.1 ).

Four trials (520 participants) evaluated the effect on response of a telephone reminder in addition to a postal reminder compared to a postal reminder only. The odds of response were increased by more than one‐half when a telephone reminder was included (OR 1.63; 95% CI 1.06 to 2.50). There was moderate heterogeneity amongst the trial results (I 2 = 26%) ( Analysis 107.2 ). Five trials (24,373 participants) evaluated the effect on response to a web survey of an email invitation compared to a postal invitation. There was no evidence for an effect on response when using a postal invitation (OR 1.81; 95% CI 0.81 to 4.01). There was considerable heterogeneity amongst the trial results (I 2 = 98%) ( Analysis 108.2 ). A single trial (431 participants) evaluated the effect on response of intensive follow‐up (i.e. questionnaires at 1, 6 and 12 months) compared with limited follow‐up (one questionnaire at 12 months). There was no evidence for an effect on response with intensive follow‐up (OR 1.69; 95% CI 0.93 to 3.06) ( Analysis 109.1 ).

Two trials (771 participants) evaluated the effect on response of a pre‐contact SMS (on the day of mailing) compared to a post‐notification SMS (a few days following mailing). There was no evidence for an effect on response when a post‐notification SMS was used (OR 1.29; 95% CI 0.66 to 2.54). There was moderate heterogeneity amongst the trial results (I 2 = 56%) ( Analysis 110.2 ). A single trial (5837 participants) evaluated the effect on response of sending a postal questionnaire with an electronic reminder compared to sending an e‐questionnaire with a postal reminder. There was no evidence of an effect on response when participants were sent an e‐questionnaire with a postal reminder (OR 1.05; 95% CI 0.95 to 1.16) ( Analysis 111.2 ). A single trial (296 participants) evaluated the effect on response of giving study participants a calendar with prompts for when to return questionnaires. There was no evidence for an effect on response when participants were given a calendar with prompts (OR 1.00; 95% CI 0.57 to 1.73) ( Analysis 112.2 ).

Electronic

Three trials (3,049 participants) evaluated the effect on e‐questionnaire response of contacting participants before sending questionnaires. The odds of response were almost doubled when participants were pre‐notified (OR 1.85; 95% CI 0.99 to 3.45). There was considerable heterogeneity amongst the trial results (I 2 = 80%) ( Analysis 94.4 ).

Three trials (9947 participants) evaluated the effect of an SMS reminder compared to a postcard reminder. The odds of response increased by half when an SMS reminder was used (OR 1.49; 95% CI 1.23 to 1.81). There was moderate heterogeneity amongst the trial results (I 2 = 61%) ( Analysis 113.1 ). Three trials (7,159 participants) evaluated the effect on questionnaire response of follow‐up contact with participants by email compared with a mixed‐mode reminder (email and postal). The odds of response were doubled when a mixed‐mode reminder was used (OR 1.96; 95% CI 0.89 to 4.31). There was, however, considerable heterogeneity between the trial results (I 2 = 94%) ( Analysis 114.2 ).

A single trial (734 participants) evaluated the effect on response of using a mixed‐mode first contact compared to electronic only. The odds of response were increased by half with a mixed‐mode first contact (OR 1.54; 95% CI 1.15 to 2.07) ( Analysis 115.2 ).

One trial (500 participants) evaluated the effect on e‐questionnaire response of contacting participants by letter before sending e‐questionnaires compared to pre‐contact by postcard. There was no evidence for an effect on response when participants were pre‐contacted by postcard instead of by letter (OR 1.38; 95% CI 0.76 to 2.49) ( Analysis 101.3 ). Four trials (26,482 participants) evaluated the effect on response of push‐to‐web (i.e. where initial requests are sent by post and participants are asked to complete questionnaires over the Web) compared to providing a choice of response modes (i.e. electronic or postal response). There was no evidence for an effect on response when providing a choice of response modes (electronic or postal response) compared to push‐to‐web (OR 1.09; 95% CI 0.99 to 1.20). There was moderate heterogeneity between the trial results (I 2 = 34%) ( Analysis 116.2 ).

A single trial (3508 participants) evaluated the effect on response of push‐to‐web (i.e. where initial requests are sent by post and participants are asked to complete questionnaires over the Web) compared to mail only. The odds of response were increased by one‐quarter using mail only (OR 1.26; 95% CI 1.10 to 1.45) ( Analysis 117.2 ). The same trial evaluated the effect on response of mail‐push (initial mail contact with reminders of the paper questionnaire and an option to complete the survey online) compared to mail only. There was no evidence for an effect on response when mail‐push was used (OR 0.96; 95% CI 0.84 to 1.10) ( Analysis 118.2 ).

A single trial (2982 participants) evaluated the effect on response of email augmentation of push‐to‐web (i.e. the addition of emailed versions of the advance letter and reminders, where participants are asked to complete questionnaires over the Web) compared with push‐to‐web without email augmentation. There was no evidence for an effect on response with email augmentation (OR 1.13; 95% CI 0.98 to 1.31) ( Analysis 119.1 ).

A single trial (178 participants) evaluated the effect on response of sending an SMS reminder with a link to the e‐questionnaire compared to sending an SMS reminder without a link. There was no evidence for an effect on response when participants were sent an SMS reminder with a link (OR 1.00; 95% CI 0.55 to 1.82) ( Analysis 120.2 ). A single trial (125 participants) evaluated the effect on response of sending an electronic prompt (email or SMS). There was no evidence for an effect on response when participants were sent an electronic prompt (OR 1.27; 95% CI 0.47 to 3.48) ( Analysis 121.1 ).

Content ‐ Nature and style of questions (Strategies 122‐143)

Postal

Ten trials (21,393 participants) evaluated the effect on response of including a ’sensitive’ question in a questionnaire. The odds of response were reduced by nearly one‐tenth when sensitive questions were included (OR 0.94; 95% CI 0.88 to 1.00) ( Analysis 122.2 ). A single trial (5817 participants) evaluated the effect on response of placing the more relevant questions at the start of the questionnaire. The odds of response were increased by a quarter when more relevant questions were placed first (OR 1.23; 95% CI 1.10 to 1.37) ( Analysis 123.2 ). Three trials (11,435 participants) evaluated the effect on response of placing the most general questions at the start of the questionnaire. There was no evidence for an effect on response of placing general questions first (OR 0.95; 95% CI 0.83 to 1.09) ( Analysis 124.1 ). Five trials (10,565 participants) evaluated the effect on questionnaire response of placing questions asking for demographic information first. There was no evidence for an effect on response of placing demographic items first (OR 1.02; 95% CI 0.90 to 1.16) ( Analysis 125.2 ). Two trials (3182 participants) evaluated the effect on response of placing the easiest questions at the start of the questionnaire. The odds of response were increased by over a half when the easiest questions were presented first (OR 1.61; 95% CI 1.14 to 2.26) ( Analysis 126.2 ). Two trials (4087 participants) evaluated the effect on response of using a more ’user‐friendly’ questionnaire. The odds of response were increased by almost half using user‐friendly questionnaires (OR 1.47; 95% CI 1.25 to 1.73) ( Analysis 127.2 ). Four trials (6491 participants) evaluated the effect on response of using a more ’interesting’ or high salient questionnaire (e.g. asking questions particularly relevant to the study participants). The odds of response were nearly doubled using more interesting/salient questionnaires (OR 1.73; 95% CI 1.12 to 2.66). There was considerable heterogeneity between the trial results (I 2 = 91%) ( Analysis 128.2 ). Four trials (3092 participants) evaluated the effect on questionnaire response of using open‐ended rather than closed questions. The odds of response were reduced by more than half when open‐ended questions were used (OR 0.43; 95% CI 0.19 to 0.98). There was considerable heterogeneity between the trial results (I 2 = 95%) ( Analysis 129.2 ). One trial (300 participants) evaluated the effect of using open‐ended items first compared to other items first. There was no evidence for an effect on response of using open‐ended items first (OR 1.26; 95% CI 0.73 to 2.19) ( Analysis 130.2 ). The same trial (300 participants) evaluated the effect of using closed‐ended items first compared to other items first. There was no evidence for an effect on response of using closed‐ended items first (OR 0.93; 95% CI 0.54 to 1.59) ( Analysis 131.2 ). A single trial (1360 participants) evaluated the effect on response of including ’don’t know’ boxes for questions. There was no evidence for an effect on response of including ’don’t know’ boxes (OR 1.03; 95% CI 0.82 to 1.29) ( Analysis 132.1 ). Two trials (1125 participants) evaluated the effect on response of using a “circle answer” rather than “tick box” format on question responses. There was no evidence for an effect on response of using a circle answer format (OR 0.96; 95% CI 0.74 to 1.26) ( Analysis 133.1 ). A single trial (6783 participants) evaluated the effect of listing response options in increasing order on questionnaire response. There was no evidence for an effect on response of listing response options in increasing order (OR 1.06; 95% CI 0.94 to 1.18) ( Analysis 134.1 ). Two trials (3882 participants) evaluated the effect on response of using high‐frequency response alternatives compared to medium‐frequency response alternatives. There was no evidence for an effect on response when high‐frequency response alternatives were used (OR 1.40; 95% CI 0.58 to 3.38). There was considerable heterogeneity between the trial results (I 2 = 85%) ( Analysis 135.1 ). Another trial (654 participants) evaluated the effect on questionnaire response of using a 5‐step response scale compared to a 10‐step response scale. There was no evidence for an effect on response of using a 5‐step response scale (OR 0.78; 95% CI 0.52 to 1.19) ( Analysis 136.1 ). A single trial (1500 participants) evaluated the effect of using an individual‐item rather than a stem‐and‐leaf format on questionnaire response. There was no evidence for an effect on response of using an individual item format (OR 0.88; 95% CI 0.70 to 1.10) ( Analysis 137.1 ). One trial (400 participants) evaluated the horizontal orientation of response options compared to vertical orientation of response options. The odds of response were three times greater when horizontal rather than vertical orientation was used (OR 3.12; 95% CI 1.63 to 5.96) ( Analysis 138.1 ). Four trials (7345 participants) evaluated the effect on response of using a conventional mode of response technique compared to a randomised response technique. There was no evidence for an effect on response of using the conventional mode of response technique (OR 1.52; 95% CI 0.85 to 2.72) ( Analysis 139.2 ). A single trial (1280 participants) evaluated the effect on response of asking ’factual’ questions only compared to factual and attitudinal questions. The odds of response were increased by more than a quarter using factual questions only (OR 1.34; 95% CI 1.01 to 1.77) ( Analysis 140.1 ). One trial (200 participants) evaluated the effect on response of using a multi‐option consent form compared to a standard consent form. There was no evidence for an effect on response of using a multi‐option consent form (OR 0.91; 95% CI 0.49 to 1.68) ( Analysis 141.1 ). One trial (259 participants) evaluated the effect on response of questions ordered by time period compared to those not ordered by time period. There was no evidence for an effect on response of using questionnaires where questions are ordered by time period (OR 1.48; 95% CI 0.84 to 2.59) ( Analysis 142.1 ). Two trials (226 participants) evaluated the effect on response of placing clinical outcome questions first compared to placing them last. The odds of response were doubled when clinical outcome questions were last (OR 2.05; 95% CI 0.99 to 4.25) ( Analysis 143.2 ).

Electronic

One trial (2176 participants) evaluated the effect on response of using a more 'interesting' e‐questionnaire (e.g. asking questions particularly relevant to the study participants). The odds of response were almost doubled using a more interesting e‐questionnaire (OR 1.85; 95% CI 1.52 to 2.26) ( Analysis 128.3 ).

Origin ‐ Who sent the questionnaire? (Strategies 144‐150)

Postal

Fourteen trials (21,628 participants) evaluated the effect on response of university sponsorship. The odds of response were increased by more than a quarter when questionnaires originated from a university rather than an alternative source, such as a government department or commercial organisation (OR 1.32; 95% CI 1.13 to 1.54). There was considerable heterogeneity between trial results (I 2 = 83%) ( Analysis 144.2 ). Eleven trials (5686 participants) evaluated the effect on response when questionnaires were sent or signed by a more senior or well‐known person. There was no evidence for an effect on response when a more senior or well‐known person sent or signed the questionnaire (OR 1.05; 95% CI 0.90 to 1.23). There was moderate heterogeneity between the trial results (I 2 = 41%) ( Analysis 147.2 ).

A single trial (500 participants) evaluated the effect on questionnaire response of sending the questionnaire in a university‐printed envelope. There was no evidence for an effect on response of sending the questionnaire in a university‐printed envelope (OR 0.88; 95% CI 0.61 to 1.28) ( Analysis 146.2 ). Two trials (924 participants) evaluated the effect on response of pre‐contact by a medical researcher compared to a nonmedical researcher. There was no evidence for an effect on response of pre‐contact by a medical researcher (OR 1.01; 95% CI 0.55 to 1.86). There was considerable heterogeneity between the trial results (I 2 = 72%) ( Analysis 148.1 ). Two trials (1106 participants) evaluated the effect on response when questionnaires were sent from a GP rather than a research group. There was no evidence for an effect on response of sending questionnaires by a GP (OR 1.52; 95% CI 0.73 to 3.15). There was considerable heterogeneity between the trial results (I 2 = 84%) ( Analysis 149.2 ). Five trials (5959 participants) evaluated the effect on response of whether the ethnicity of the name of the person sending the questionnaire was identifiable. There was no evidence for an effect on response when names were ethnically identifiable (OR 1.07; 95% CI 0.90 to 1.27) ( Analysis 180.2 ). Two trials (3146 participants) evaluated the effect of sending the questionnaire from a male investigator compared to a female investigator. There was no evidence for an effect on response of sending the questionnaire from a male investigator (OR 1.07; 95% CI 0.72 to 1.58) ( Analysis 150.2 ).

Electronic

Two trials (3845 participants) evaluated the effect on e‐questionnaire response of university sponsorship. There was no evidence for an effect on e‐questionnaire response by using university sponsorship (OR 0.84; 95% CI 0.69 to 1.01) ( Analysis 144.4 ). Two trials (658 participants) evaluated the effect on e‐questionnaire response of ‘higher’ university sponsorship (i.e. university logo featured prominently on every page of the surveys) compared with ‘lower’ university sponsorship (i.e. university logo did not appear anywhere on the surveys, although its name was mentioned in the information sheets). There was no evidence for an effect on response of using ‘higher’ university sponsorship (OR 0.96; 95% CI 0.63 to 1.45) ( Analysis 145.1 ).

Two trials (720 participants) evaluated the effect of sending the e‐questionnaire from a male compared to a female investigator. The odds of response decreased by over a half when the e‐questionnaire was from a male investigator (OR 0.55; 95% CI 0.38 to 0.80) ( Analysis 150.3 ). Six trials (28,162 participants) evaluated the effect on response when e‐questionnaires were sent or signed by a more senior or well‐known person. There was no evidence for an effect on response when a more senior or well‐known person sent or signed the e‐questionnaire (OR 1.09; 95% CI 0.96 to 1.25). There was moderate heterogeneity amongst the trial results (I 2 = 41%; I 2 = 69%) ( Analysis 147.4 ).

Communication ‐ What are participants told? (Strategies 151‐178)

Postal

One trial (25,000 participants) evaluated the effect on questionnaire response of providing participants with an assurance of confidentiality. The odds of response were increased by more than a quarter with an assurance of confidentiality (OR 1.33; 95% CI 1.24 to 1.42) ( Analysis 151.1 ). One trial (468 participants) evaluated the effect on questionnaire response of including a statement that others had responded to. There was no evidence for an effect on response when the statement was included (OR 1.12; 95% CI 0.76 to 1.65) ( Analysis 152.2 ). Five trials (5544 participants) evaluated the effect on questionnaire response of offering participants the choice to opt out of the study. There was no evidence for an effect on response when participants could opt out (OR 0.96; 95% CI 0.74 to 1.25). There was considerable heterogeneity between the trial results (I 2 = 80%) ( Analysis 153.2 ).

A single trial (2000 participants) evaluated the effect on response of providing instructions for completion of the questionnaire. There was no evidence for an effect on response when instructions were given (OR 0.89; 95% CI 0.74 to 1.06) ( Analysis 154.1 ). Six trials (5661 participants) evaluated the effect on response of giving participants a deadline by which to respond. There was no evidence for an effect on response of giving a deadline (OR 1.00; 95% CI 0.84 to 1.19). There was moderate heterogeneity between the trial results (I 2 = 48%) ( Analysis 155.2 ). Three trials (600 participants) evaluated the effect on response of mention of an obligation to respond compared to no mention of an obligation to respond. The odds of response increased by more than half with the mention of an obligation to respond (OR 1.61; 95% CI 1.16 to 2.22) ( Analysis 156.2 ).

One trial (702 participants) evaluated the effect on response of questionnaires including a request for a telephone number. There was no evidence for an effect on response of requesting a telephone number (OR 1.00; 95% CI 0.65 to 1.54) ( Analysis 157.2 ). One trial (200 participants) evaluated the effect of asking participants to respond on the questionnaire itself compared to asking them to respond on a separate form. There was no evidence for an effect on response of asking the participants to respond on the questionnaire rather than on a separate form (OR 1.13; 95% CI 0.57 to 2.27) ( Analysis 158.2 ).

Seven trials (7053 participants) evaluated the effect on questionnaire response of telling participants that they would be contacted again if they did not respond. There was no evidence for an effect on response if mention of follow‐up was used (OR 1.02; 95% CI 0.91 to 1.15) ( Analysis 159.2 ). Two trials (1907 participants) evaluated the effect on questionnaire response of requesting an explanation for non‐participation. There was no evidence for an effect on response of requesting an explanation for non‐participation (OR 1.14; 95% CI 0.83 to 1.57). There was moderate heterogeneity amongst the trial results (I 2 = 62%) ( Analysis 160.2 ). One trial (600 participants) evaluated the effect on response of providing a time estimate for completion of the questionnaire. There was no evidence for an effect on response when a time estimation was provided (OR 1.10; 95% CI 0.76 to 1.58) ( Analysis 161.2 ).

One trial (500 participants) evaluated the effect on response of a detailed cover letter compared to a brief cover letter. There was no evidence for an effect on response by using the detailed cover letter (OR 1.08; 95% CI 0.74 to 1.58) ( Analysis 162.2 ). Two trials (1251 participants) evaluated the effect on response of the presence of an appeal or a pleading factor in the cover letter. There was no evidence for an effect on response of using an appeal (OR 1.06; 95% CI 0.79 to 1.42) ( Analysis 163.1 ). One trial (100 participants) evaluated the effect of a note requesting participants not to remove an ID Code. The odds of response decreased by more than a half when the note was added (OR 0.37; 95% CI 0.14 to 0.96) ( Analysis 164.2 ).

A single trial (201 participants) evaluated the effect on response of a request for the participant’s signature. There was no evidence of an effect on response when participants’ signatures were requested (OR 1.19; 95% CI 0.65 to 2.18) ( Analysis 165.1 ). Another trial (395 participants) evaluated the effect of endorsing the questionnaire by eminent professionals in the field. The odds of response decreased by more than a quarter when an endorsement was used (OR 0.63; 95% CI 0.43 to 0.94) ( Analysis 166.2 ). One trial (671 participants) evaluated the effect of a veiled threat in follow‐up letters. The odds of response doubled when a veiled threat was used (OR 2.09; 95% CI 1.49 to 2.93) ( Analysis 167.2 ). Eight trials (10,908 participants) evaluated the effect on questionnaire response of stressing how response would benefit the sponsor. There was no evidence for an effect on response when stressing the benefits to the sponsor (OR 0.99; 95% CI 0.86 to 1.13). There was moderate heterogeneity amongst the trial results (I 2 = 56%) and both Begg’s and Egger’s tests indicated evidence of selection bias ( Analysis 168.2 ). Ten trials (15,159 participants) evaluated the effect on questionnaire response of stressing how response would benefit the participant. There was no evidence for an effect on response when stressing the benefits to participants (OR 1.00; 95% CI 0.85 to 1.17). There was considerable heterogeneity amongst the trial results (I 2 = 78%) ( Analysis 169.2 ).

Fourteen trials (36,107 participants) evaluated the effect on questionnaire response of stressing how response would benefit society. There was no evidence for an effect on response of stressing the benefits to society (OR 1.07; 95% CI 0.95 to 1.20). There was considerable heterogeneity between trial results (I 2 = 72%) and both Begg’s and Egger’s tests indicated evidence of selection bias ( Analysis 170.2 ). Two trials (2070 participants) evaluated the effect on response of questionnaires remaining anonymous compared with being identifiable. There was no evidence for an effect on response of questionnaires remaining anonymous (OR 0.96; 95% CI 0.66 to 1.39). There was considerable heterogeneity between the trial results (I 2 = 72%) ( Analysis 171.1 ).

Two trials (27,119 participants) evaluated the effect on response of using a cover letter that highlighted salience. There was no evidence for an effect on response of a letter that highlighted salience (OR 1.06; 95% CI 0.75 to 1.50). There was considerable heterogeneity between the trial results (I 2 = 75%) ( Analysis 172.2 ). A single trial (2180 participants) evaluated the effect on response by using a cover letter that highlighted salience in the first mailing compared with using one during follow‐up. The odds of response when using a cover letter that highlights salience in the first mailing were over twice the odds of response when one was used during follow‐up (OR 2.49; 95% CI 1.82 to 3.40) ( Analysis 173.3 ).

One trial (4447 participants) evaluated the effect on questionnaire response of informing participants that their responses were being monitored. The odds of response were increased by more than a tenth when the letter stated that responses were being monitored (OR 1.15; 95% CI 1.01 to 1.31) ( Analysis 174.2 ). A single trial (1418 participants) evaluated the effect on response of using a cover letter that emphasised harm prevention compared with one that emphasised health promotion. There was no evidence of an effect on response when the letter emphasised harm prevention (OR 1.19; 95% CI 0.83 to 1.72) ( Analysis 175.2 ). The same trial evaluated the effect on response of using a cover letter that emphasised harm prevention compared with one that contained a neutral message. The odds of response were increased by more than two‐fifths when the letter emphasised harm prevention (OR 1.44; 95% CI 0.98 to 2.12) ( Analysis 176.2 ).

One trial (1192 participants) evaluated the effect on questionnaire response by sending a letter with behaviour change techniques in the text. The odds of response were increased by more than a quarter using the letter with behaviour change techniques in the text (OR 1.39; 95% CI 1.08 to 1.77) ( Analysis 177.1 ). A single trial (1316 participants) evaluated the effect on response of using a culturally sensitive cover letter. There was no evidence for an effect on response using a culturally sensitive cover letter (OR 1.00; 95% CI 0.74 to 1.34) ( Analysis 179.1 ).

Electronic

Three trials (23,777 participants) evaluated the effect on e‐questionnaire response by including a statement that others had responded to. There was no evidence for an effect on response when the statement was included (OR 1.14; 95% CI 0.83 to 1.56). There was considerable heterogeneity between the trial results (I 2 = 94%) ( Analysis 152.4 ).

A single trial (8586 participants) evaluated the effect on e‐questionnaire response of giving participants a deadline by which to respond. The odds of response increased by over a tenth when given a deadline (OR 1.18; 95% CI 1.03 to 1.34) ( Analysis 155.4 ). Three trials (3536 participants) evaluated the effect on e‐questionnaire response by stressing how responses would benefit society. There was no evidence for an effect on response when stressing the benefits to society (OR 1.35; 95% CI 0.95 to 1.91). There was moderate heterogeneity between trial results (I 2 = 41%) ( Analysis 170.3 ). Four trials (5915 participants) evaluated the effect of including an appeal, such as “request for help” in the subject line of the email. There was no evidence of an effect on response by including an appeal in the subject line (OR 1.07; 95% CI 0.79 to 1.47). There was considerable heterogeneity between the trial results (I 2 = 71%) ( Analysis 163.3 ).

A single trial (1250 participants) evaluated the effect on e‐questionnaire response of a detailed letter compared to a brief letter. The odds of response were over three times greater when using the brief letter (OR 3.26; 95% CI 1.79 to 5.94) ( Analysis 162.3 ). One trial (2358 participants) evaluated the effect on response of telling participants that the e‐questionnaire would take 10 minutes to complete compared with telling them that it would take 30 minutes. There was no evidence for an effect on response by giving a longer time estimate (OR 1.25; 95% CI 0.96 to 1.64) ( Analysis 178.2 ).

Length ‐ How long is the questionnaire? (Strategies 183‐87)

Postal

Seventy‐two trials (84,954 participants), including two unpublished trials, evaluated the effect of questionnaire length on response. The odds of response increased by more than half using shorter questionnaires (OR 1.58; 95% CI 1.40 to 1.78). Heterogeneity amongst trial results was apparent on inspection of the forest plot, and in the Chi2 test result (P < 0.00001) and I 2 result (93%) ( Analysis 183.2 ). One trial (600 participants) evaluated the effect on questionnaire response of using a double postcard compared to one page. The odds of response decreased by half when a double postcard was used (OR 0.47; 95% CI 0.34 to 0.66) ( Analysis 184.2 ). A single trial (1795 participants) evaluated the effect of sending the questionnaire with a supplement compared to sending the questionnaire alone. There was no evidence for an effect on response of sending a questionnaire with a supplement (OR 0.86; 95% CI 0.70 to 1.07) ( Analysis 185.1 ). Two trials (4943 participants) evaluated the effect on response of including a questionnaire for relatives. The odds of response were reduced by one‐third when a questionnaire for relatives was included (OR 0.67; 95% CI 0.60 to 0.76) ( Analysis 186.1 ). One trial (414 participants) evaluated the effect of including a consent form with the questionnaire. There was no evidence for an effect on response of including a consent form (OR 1.32; 95% CI 0.89 to 1.95) ( Analysis 187.2 ).

Electronic

Five trials (12,325 participants) evaluated the effect of the length of electronic questionnaires on response. The odds of response increased by half when using shorter e‐questionnaires (OR 1.51; 95% CI 1.06 to 2.16). There was considerable heterogeneity amongst the trial results (I 2 = 94%) ( Analysis 183.4 ).

Discussion

Summary of main results

This updated review identified a total of 758 eligible studies that evaluated 187 strategies to increase response to postal and electronic questionnaires, adding 245 new trials to the 513 studies included in the previously published version ( Edwards 2009 ). We found substantial heterogeneity amongst trial results in half of the strategies.

The findings relevant to increasing questionnaire response include: contacting people before they are sent the questionnaire, sending postal questionnaires by first‐class post or by a special (recorded) delivery service, and providing a stamped‐return envelope. Questionnaires, letters, and emails can be made more personal, and kept short; incentives can be offered with a postal questionnaire, for example, a small amount of money, or a non‐monetary incentive such as a pen; one or more reminders can be sent with a copy of the questionnaire to people who do not reply; response to postal questionnaires can also be increased if they originate from a university. Using postal rather than electronic questionnaires or providing people with a choice of response modes (electronic or postal) can increase response. Response to an electronic questionnaire can be increased if it is administered over a computer rather than a smartphone. Monetary and non‐monetary incentives can also help to increase response to electronic questionnaires.

We have chosen to use odds ratios in our analyses for methodological reasons. However, the practical implication of the odds ratio for a strategy is difficult to interpret without knowing the baseline response rate (without the strategy). Moreover, the odds ratio for a strategy might vary in relationship to the baseline response rate. Therefore, those conducting postal and electronic surveys should scrutinise the data in the relevant results tables closely if the magnitude of the effect that they might expect from using a specific strategy is an important consideration for them in deciding whether to use the strategy. A table showing the conversion of odds ratios to response proportions for a range of different baselines is included in Appendix 2 .

Summary of evidence since last published version

Many of the 245 new trials added to this review update evaluated previously identified strategies (e.g. incentives, length, and personalisation). Many of the effect estimates of strategies to increase questionnaire response presented in this update are similar to those reported in the last published version of the review ( Edwards 2009 ) but are now more precise (i.e. confidence intervals are narrower now than before). In a few cases, the addition of new trials changed our conclusions: for example, there is now some evidence for an effect on postal questionnaire response by using a larger non‐monetary incentive; also, there is now evidence that monetary incentives increase electronic questionnaire response. Strategies that emerged in this update that were not reported previously are: using postal rather than electronic questionnaires and providing people with a choice of response modes (electronic or postal) can increase response.

Overall completeness and applicability of evidence

We found 670 eligible trials with postal questionnaires that evaluated over 100 different ways of increasing response and 88 eligible trials with electronic questionnaires that evaluated over 30 different ways of increasing response. The types of participants in these trials include a wide range of people likely to be asked to complete a questionnaire, from clinical trial participants, patients and healthcare providers, university students and faculty, to marketing managers, industrial accountants, microwave oven owners, and grocery store managers. All trials reported the required outcomes: the proportions of participants responding to the first or final mailings of a postal questionnaire, and the proportions of participants logging‐in, clicking a hyperlink, or submitting an online questionnaire.

Inadequate allocation concealment can bias the results of clinical trials ( Schulz 1995 ). In our review, information on allocation concealment was unavailable for most of the included trials. If they were inadequately concealed, this may have biased the results. Blinding of outcome assessors reduces detection bias ( Higgins 2022 ). However, in the eligible trials in our review update, no outcomes were assessed because we were only interested in the counts of responses in the experimental and control groups, and so there was little or no risk of detection bias in this review.

Quality of the evidence

As all the included studies were randomised trials, the overall quality of the body of evidence presented in this review is ‘high’. However, we found considerable statistical heterogeneity amongst trial results in half of the strategies, and for these, the pooled odds ratios may not be meaningful. Variation between trial interventions and populations is likely to explain some of the heterogeneity. For example, amongst trials evaluating non‐monetary incentives, the types of incentives used are considerably heterogeneous, including things such as donations to charity, lottery participation, and a free key‐ring or pen. Amongst trials evaluating monetary incentives, the amounts of money offered to participants varied between trials. A meta‐regression analysis has shown that monetary incentives can increase response to postal questionnaires but that the relationship between the amount of money and response is not linear ( Edwards 2005 ). Amongst the trials evaluating shorter and longer questionnaires, the length of the questionnaires used varied between trials, some comparing a single page with a two‐page alternative, and others comparing four or more pages with longer alternatives. In a meta‐regression analysis, most of the heterogeneity in trial results was explained by variation in the length of the questionnaires used in each trial ( Edwards 2004 ). A subgroup analysis of the trials of personalisation in postal questionnaires found that response was increased by addressing participants by name on cover letters, and that the effect appeared to be enhanced by including a handwritten signature ( Scott 2006 ). Due to the remaining unexplained heterogeneity in other strategies, we downgraded the overall quality rating of the body of evidence presented in this review to ‘moderate’.

Potential biases in the review process

The identification and inclusion of all relevant trials in systematic reviews reduces random error in meta‐analyses and, because ease of identification of trials is associated with intervention effects, complete ascertainment may also reduce bias ( Clarke 1994 ). We excluded some trials because we could not confirm that participants had been randomly allocated to intervention and control groups, and we have not examined whether the results of these trials differed systematically from the included trials. Although tests for selection bias were significant in fifteen strategies, these results may be due to true heterogeneity between trial results, rather than bias in the selection of trials ( Egger 1997 ).

Agreements and disagreements with other studies or reviews

Two other systematic reviews and one meta‐analysis of methods to increase questionnaire response have appeared in the survey research literature during the 30 years prior to this review.

The largest of these ( Yammarino 1991 ) included 115 studies published between 1940 and 1988. It also found evidence that: repeated contacts (preliminary notification and follow‐up), appeals in letters, inclusion of a return envelope, types of postage, monetary incentives (particularly $0.50 or less), and shorter questionnaires increased response. However, it did not find evidence that either sponsorship or non‐monetary incentives increased response. It is unclear in this meta‐analysis whether only RCTs were included, which, in addition to the smaller number of included studies, may explain why its findings differ from those of our review.

The next largest ( Price 2022 ) included 40 randomised trials of patient experience surveys only, conducted in the US. It presented a descriptive account of the included studies with no meta‐analysis. As in our review, it concluded the following: that pre‐notification, special delivery, and monetary incentives (particularly unconditional ones) increased response; it also found evidence that questionnaires administered using web‐based modes only resulted in lower response rates than those administered by mail. Unlike our review, however, it was uncertain about any effects of questionnaire length on response.

The third ( Nakash 2006 ) included 13 randomised trials of healthcare studies on only patient populations. As in our review, it found evidence that follow‐up (particularly more intense follow‐up), and shorter questionnaires increased response. Unlike our review, however, it found no evidence for any effects of incentives on response. The reason for this different result may be that it only included four trials of non‐monetary incentives. Our review includes 146 trials of non‐monetary incentives and shows that the odds of response can be increased by over a tenth when a non‐monetary incentive is used.

The most likely reason for differences in the findings of our review with those of the reviews described above is the huge difference in the number of studies included.

Authors' conclusions

Implication for systematic reviews and evaluations of healthcare

Researchers can increase response to postal and electronic questionnaires by using the strategies shown to be effective in this systematic review. Some strategies will require additional materials or administrative time whereas others can be implemented at little or no extra cost. For example, researchers may be able to double the odds of response by offering participants payment for completion of questionnaires or by using recorded delivery, both of which will add substantially to costs for large studies. The use of non‐monetary incentives, on the other hand, may be more affordable, but is likely to be less effective in encouraging response.

Implication for methodological research

Further analyses (for example, using random‐effects meta‐regressions) may reveal important sources of variation, for example, due to methodological quality, questionnaire topic, the years in which each study was done, or types of population. In this review, our aim was to systematically identify and critically appraise eligible trials, and to present the relevant data. We did not intend to produce single effect estimates for every strategy. For many strategies, although there was statistical heterogeneity, the directions of the effects were similar. For these strategies, we cannot be sure about the size of the effect, but we can be reasonably confident that there was an effect on response.

The results of this review show that questionnaire length has a substantial impact on non‐response, particularly when questionnaires are very short. In the context of outcome data collection in a clinical trial, the use of a short questionnaire would be expected to minimise non‐response, thus increasing the effective sample size and reducing sampling error. However, if the use of short questionnaires reduces the accuracy of the measurement process, the reduction in random error achieved by increased follow‐up would have to be traded‐off against increased random error due to using less precise measurements. Further research is underway by the authors to quantify this trade‐off, so that outcome measures can be designed for use in clinical trials that minimise total random error (sampling error and measurement error).

This review examined the effectiveness of 187 different strategies to increase the response to postal and electronic questionnaires. The outcome of interest in this review was the overall response proportion, and we did not examine the impact of factors that may influence the completeness of the returned questionnaires. However, factors that influence the readability of questionnaires, such as the number of syllables per word, words per sentence, typeface and font size may have an important effect on both the proportion of questions that are answered and indeed the overall response proportion.

One‐third of clinical trials, case‐control and cohort studies collect data from participants using a questionnaire, and more than a quarter collect data using interviews with participants ( Van Gelder 2010 ). If those who are eligible for a study or those who agree to take part do not respond to these questionnaires or refuse to take part in interviews, this will reduce study power and may introduce bias in the results that makes them misleading and useless. Good evidence exists in this review for some methods that might be used to increase response to self‐completed questionnaires, and this evidence has been used to achieve over 90% data completion in some biomedical research studies ( Butler 2013 ; Edwards 2005b ; Free 2011 ). However, less is known about effective methods to increase participation in interviews, and we plan to conduct a Cochrane Methodology Review to address this gap in the evidence.

What's new

History

Protocol first published: Issue 2, 1999 Review first published: Issue 3, 2001

Acknowledgements

This Cochrane review was originally supported by a grant from the BUPA Foundation and by a Nuffield Trust Short Term Fellowship and was initially conducted with support from Cochrane Injuries (closed in March 2023). The initial motivation for the review came from the need to find ways to ensure high rates of follow‐up in the MRC CRASH‐1 Trial.

Sir Iain Chalmers, Professor Peter Sandercock, Professor Catherine Peckham, and the MRC CRASH‐1 Trial Management Group were acknowledged for their help and advice with the first version of the review (see Edwards 2009 ). The 2008 update to this review was supported by a second grant from the BUPA Foundation (see Edwards 2009 ). We also wish to acknowledge the help of Reinhard Wentz, Sarah Pratap, Irene Kwan, Rachel Cooper, and Lambert Felix, who all assisted in previous versions of the review. This review update was funded by the National Institute for Health and Care Research (NIHR) Evidence Synthesis Programme (NIHR133238) Programme Grant Scheme. The views expressed are those of the author(s) and not necessarily those of the NIHR or the Department of Health and Social Care.

Editorial and peer‐review contributions

Cochrane Methodology supported the authors in the development of this review update. The following people conducted the editorial process for this review update:

Sign‐off Editor (final editorial decision): Tari Turner, Cochrane Australia;

Managing Editor (provided editorial guidance to authors, edited the article): Joey Kwong, Cochrane Central Editorial Service;

Editorial Assistant (conducted editorial policy checks, selected peer reviewers, collated peer‐reviewer comments, supported editorial team): Sara Hales‐Brittain, Cochrane Central Editorial Service;

Copy Editor (copy editing and production): Anne Lethaby, c/o Cochrane Central Production Service;

Peer‐reviewers (provided comments and recommended an editorial decision): David Torgerson, York Trials Unit, Department of Health Sciences, University of York (clinical/content review); Patrick C. Hardigan, Kiran C. Patel College of Allopathic Medicine, Nova Southeastern University (clinical/content review); Brian Duncan (consumer review); Jennifer Hilgart, Cochrane Evidence Production & Methods Directorate (methods review); Steve McDonald, Cochrane Australia (search review).

Appendices

Appendix 1. Search strategies

Original review

Search strategies were developed for use in a range of electronic bibliographic databases in Edwards 2003 .

Database time period or version

Cochrane Controlled Trials Register 1999.3 CINAHL 1982 ‐ 1999.07 ERIC 1982 ‐ 1998.09 PsycLit 1887 ‐ 1999.09 Dissertation Abstracts 1861 ‐ 1999.08 MEDLINE 1966 ‐ 1999 EMBASE 1980 ‐ 1999.08

A. questionnair* or survey* or data collection B. respon* or return* C. remind* or letter* or postcard* or incentiv* or reward* or money* or monetary or payment* or lottery or raffle or prize or personalis* or sponsor* or anonym* or length or style* or format or appearance or color or colour or stationery or envelope or stamp* or postage or certified or registered or telephon* or telefon* or notice or dispatch* or deliver* or deadline or sensitive D. control* or randomi* or blind* or mask* or trial* or compar* or experiment* or "exp" or factorial E. A and B and C and D

Social Science Citation Index 1981 ‐ 1999 Science Citation Indes 1981 ‐ 1999 [(survey* or questionnair*) and (return* or respon*)]

Social Psychological Educational Criminological Trials Register (SPECTR) 1950 ‐ 1998 EconLit 1969 ‐ 2000 Sociological Abstracts 1963 ‐ 2000

((survey$ or questionn$) and (return$ or respon$)).ti or ((survey$ or questionn$) and (mail$ or post$)).ti or ((return$ or respon$) and (mail$ or post$)).ti

Index to Scientific & Technical Proceedings 1982 ‐ 2000

((survey*, questionn*)+(return*,respon*))@TI, ((return*,respon*)+(mail,mailed,postal))@TI, ((survey*,questionn*)+(mail,mailed,postal))@TI

National Research Register (Web version): 2000.1

((survey*:ti or questionn*:ti) and (return*:ti or respon*:ti)) or ((return*:ti or respon*:ti) and (mail:ti or mailed:ti or postal:ti)) or ((survey*:ti or questionn*:ti) and (mail:ti or mailed:ti or postal:ti))

The following literature reviews and meta‐analyses were inspected for eligible trials:

Armstrong JS. Monetary incentives in mail surveys. Public Opinion Quarterly 1975;39:111‐6.

Armstrong S. Return postage in mail surveys: a meta analysis. Public Opinion Quarterly 1987;51:233‐48.

Bogen K. The effects of questionnaire length on response rates ‐ a review of the literature. American Statistical Association 1996;1020‐5.

Boser JA. Reviewing the research on mail survey response rates: descriptive study. Paper presented at the annual meeting of the American Educational Research Association New York. April 1996.

Boser JA. Factors influencing mail survey response rates: What do we really know? Paper presented at the Annual meeting of the Mid‐South Educational Research Association. November 1995.

Brehm J. Stubbing our toes for a foot in the door? Prior contact, incentives and survey response. International Journal of Public Opinion Research 1994;6(1):45‐63.

Church AH. Estimating the effect of incentives on mail survey response rates: a meta‐analysis. Public Opinion Quarterly 1993;57:62‐79.

Cox WE. Response patterns to mail surveys. Journal of Marketing Research 1966;3:392‐7.

Downs PE. Recent evidence on the relationship between anonymity and response variables for mail surveys. Journal of the Academy of Marketing Science 1986;14(1):72‐82.

Duncan WJ. Mail questionnaires in survey research: a review of response inducement techniques. Journal of Management 1979;5(1):39‐55.

Erdos PL. Visible vs. disguised keying on questionnaires. Journal of Advertising Research 1977;17(1):13‐8.

Fox RJ. Mail survey response rate. A meta‐analysis of selected techniques for inducing response. Public Opinion Quarterly 1988;52:467‐91.

Francel EG. Mail‐administered questionnaires: a success story. Journal of Marketing Research 1966;3:89‐92.

Goyder JC. Further evidence on factors affecting response rates to mailed questionnaires. American Sociological Review 1982;47:550‐3.

Green KE. Reviewing the research on mail survey response rates: a meta‐analysis. Paper presented at the Annual Meeting of the American Educational Research Association. April 1996.

Greenwald HP. Issues in survey data on medical practice: some empirical comparisons. Public Health Reports 1986;101(5):514‐46.

Guffey H. Stamps versus postal permits: a decisional guide for return postage in mail questionnaires. Journal of Academy of Marketing Science 1980;8(3): 234‐42.

Harvey L. Factors affecting response rates to mailed questionnaires: a comprehensive literature review. Journal of the Market Research Society 1987;29:341‐53.

Heberlein TA. Factors affecting response rates to mailed questionnaires. American Sociological Review 1978;43(4):447‐62.

Hopkins KD. Response rates in survey research: a meta‐analysis of the effects of monetary gratuities. Journal of Experimental Education 1992;61:52‐62.

Houston MJ. Broadening the scope of methodological research on mail surveys. Journal of Marketing Research 1976;13:397‐403.

Jobber D. Improving response rates in industrial mail surveys. Industrial Marketing Management 1986;15:183‐95.

Jobber D. Modelling the effects of prepaid monetary incentives on mail survey response. Journal of the Operational Research Society 1988;39:365‐72.

Jobber D. Questionnaire factors and mail survey response rates. European Research. 1985;(July)124‐9.

Jobber D. Maximizing response rates in industrial mail surveys: a review of the evidence. Advances in Business Marketing 1990;4:121‐46.

Kanuk L. Mail surveys and response rates: a literature review. Journal of Marketing Research 1975;12:440‐53.

King FW. Anonymous versus identifiable questionnaires in drug usage surveys. American Psychologist 1970;25:982‐5.

Leslie L. Increasing response rates to long questionnaires. Journal of Educational Research 1970;63:347‐50.

Linsky AS. Stimulating responses to mailed questionnaires: a review. Public Opinion Quarterly 1975;39:82‐101.

Mayer EN. Postage stamps do affect results of your mailing. Printers' Ink 1946;217:91.

Nowack KM. Getting them out and getting them back. Training Development Journal 1990;(April)82‐5.

Ransdell LB. Maximising response rate in questionnaire research. American Journal of Health Behaviour 1996;20:50‐6.

Robin S. A procedure for securing returns to mail questionnaires. Sociology and Social Research 1965;50:24‐35

Roth PL. Response rates in HRM/OB survey research: norms and correlates, 1990‐1994. Journal of Management 1998;24:97‐117.

Schlegelmilch BB. Prenotification and mail survey response rates: a quantitative integration of the literature. Journal of the Market Research Society 1991;33(3):243‐55.

Scott C. Research on mail surveys. Journal of the Royal Statistical Society 1961;124:143‐205.

Singer E. Confidentiality assurances and response: a quantitative review of the experimental literature. Public Opinion Quarterly 1995;59: 66‐77.

Vaux A. Conducting mail surveys. Psychology Research Handbook. 1996:(Chapter 10).

Wiseman F. A reassessment of the effects of personalization on response patterns in mail wurveys. Journal of Marketing Research 1976;3I:110‐1.

Yammarino FJ. Understanding mail survey response behaviour: a meta‐analysis. Public Opinion Quarterly 1991;55: 613‐39.

Young JM. Improving survey response rates: a meta‐analysis of the effectiveness of an advance telephone prompt from a medical peer. Medical Journal of Australia 1999;170: 339.

Yu J. A quantitative review of research design effects on response rates to questionnaires. Journal of Marketing Research 1983;XX:36‐44.

Zelnio RN. Data collection techniques: mail questionnaires. American Journal of Hospital Pharmacy 1980;37:1113‐9.

The following journals were searched by hand:

Public Opinion Quarterly 1960 to 1998;

American Journal of Epidemiology 1948 to 1999.

Reliability of screening for eligible trials

The electronic bibliographic searches outlined above yielded several thousand records of potentially relevant reports that were then screened to determine eligibility. Because exclusion of reports during screening would mean that they would not be considered again, we assessed the accuracy and reliability of screening for relevant trials using the records retrieved by a search of ten databases.

A search of ten electronic bibliographic databases yielded 26,937 records of potentially relevant reports that were downloaded into a ProCite database. After removing duplicate records, there were 22,571 records of potentially relevant reports. These records were divided into six approximately equal sets (A to F) and each of four reviewers was allocated three of the sets to screen. The six sets were allocated such that two reviewers examined each record, and identification of trials by each reviewer could be compared with each of the other reviewers. Agreement between reviewers was assessed using Cohen's kappa statistic (k) which adjusts the proportion of records in which there was agreement between reviewers by the amount of agreement that is expected by chance alone. Ascertainment intersection (capture‐recapture) methods ( Hook 1992 ) were then used to estimate the likely number of relevant records missed by all four reviewers. When screening was complete, full copies of the reports identified by at least one reviewer as potentially relevant were requested. Each report obtained was assessed independently by two reviewers for eligibility for inclusion in the systematic review. Disagreements about eligibility were referred to a third reviewer. Eligible reports were used as the 'gold standard' against which an assessment was made about the accuracy of screening by reviewers.

After screening, 301 of 22,571 records were identified by at least one reviewer as potentially relevant. Of the six possible comparisons between reviewers, kappa coefficients of agreement ranged from 0.59 (95% CI 0.56 to 0.62) to 0.93 (95% CI 0.90 to 0.96). Agreement was 'almost perfect' (k > 0.81) between two pairs, 'substantial' (k > 0.61) between three pairs, and 'moderate' (k > 0.41) between one pair. Ascertainment intersection methods suggest that, on average, pairs of reviewers missed 4% (range 0% to 6%) of potentially relevant records. In contrast, single reviewers missed on average 22% (range 3% to 55%). Twenty‐eight reports were not available by the time of the ascertainment intersection analysis. Of the 273 reports that were available, 156 (57%) met the inclusion criteria for the systematic review. Ascertainment intersection methods estimated that pairs of reviewers had missed very few eligible records (0 records missed, 95% CI 0 to 3 records). In the light of these results, we believe that very few eligible trials were inappropriately excluded during screening.

Sensitivity of combined search strategy

The sensitivity of the search strategy was assessed by handsearching the Public Opinion Quarterly and comparing the trials identified by handsearching with those identified by the combined search strategy. Of the 40 eligible trials identified by hand searching, 15 trials had been identified from electronic bibliographic databases and 23 had been identified from the reference lists of identified trials and relevant meta‐analyses. Two studies identified by handsearching were not identified by any part of the combined search strategy. On the basis of these results, electronic bibliographic database searching had a sensitivity of 38% (15/40), searching reference lists of identified trials and relevant meta‐analyses had a sensitivity of 58% (23/40), and the combined search strategy had a sensitivity of 95% (38/40), (95% CI 84% to 99%).

* Notes on study selection: The review authors did not record the number of records/references excluded or reasons for their exclusion at the full‐text stage during the development of Edwards 2003 . There were 372 included studies and 40 studies awaiting classification.

First review update

In Edwards 2007 , the following databases were searched again using the appropriate strategies detailed above.

Database time period or version

Cochrane Controlled Trials Register 2002.4 CINAHL 1999.07 ‐ 2003.02 ERIC 1998.09 ‐ 2003.01 PsycLit 1999.09 ‐ 2003.02 Dissertation Abstracts 1999.08 ‐ 2003.02 MEDLINE 1999 ‐ 2003 EMBASE 1999.08 ‐ 2003.02 Science Citation Index 1999 ‐ 2003 Social Science Citation Index 1999 ‐ 2003 Social Psychological Educational Criminological Trials Register (SPECTR) 1998 ‐ 2003 EconLit 2000 ‐ 2003.01 Sociological Abstracts 2000 ‐ 2002.12 Index to Scientific & Technical Proceedings 2000 ‐ 2003 National Research Register (Web version): 2003.2

A search of these databases yielded 6423 records of potentially relevant reports that were downloaded into a ProCite database. Two reviewers examined each record so that identification of trials by each reviewer could be compared. After screening, 194 of 6423 records were identified by at least one reviewer as potentially relevant.

During the update, attempts were made to obtain sufficient information on studies awaiting assessment to be able to include or exclude them from the review. This included writing to or emailing the authors of all potentially eligible trials and those in studies awaiting assessment.

* Notes on study selection: The review authors did not record the number of records/references excluded (with reasons for exclusion) at the full‐text stage during the development of Edwards 2007 . This first update version included 372 trials. There were 40 studies awaiting classification.

Second review update

In Edwards 2009 , the following databases were searched again using the appropriate strategies detailed above. The search also included electronic‐based questionnaires such as those sent via email, and online surveys.

Cochrane Library Online Issue 4 2007 CENTRAL Cochrane Library Online Issue 4 2007 Methodology studies (CMR) CINAHL 2003 ‐ 2007.12 ERIC 2003 ‐ 2007.12 PsycINFO 2003 ‐ 2008.01 MEDLINE 2003 ‐ 2007.11 EMBASE 2003 ‐ 2007.10 Science Citation Index 2003 ‐ 2008.01 Social Science Citation Index 2003 ‐ 2008.01 Social Psychological Educational Criminological Trials Register (SPECTR) 2003 ‐ 2007.12 EconLit 2003 ‐ 2007.12 Sociological Abstracts 2003 ‐ 2007.12 Dissertation & Theses 2003 ‐ 2008.01 Index to Scientific & Technical Proceedings 2003 ‐ 2008.01 National Research Register (Web version): 2008.02

A search of these databases yielded 19,826 records of potentially relevant reports that were downloaded into an EndNote database. After removing duplicates, we identified 14,792 records. Two reviewers examined each record so that identification of trials by each reviewer could be compared. After screening, 253 of 14,792 records were identified by at least one reviewer as potentially relevant and their full texts were sought.

During the update, attempts were made to obtain sufficient information on studies awaiting assessment to be able to include or exclude them from the review. This included writing to or emailing the authors of all potentially eligible trials and those studies awaiting assessment.

* Notes on study selection: The review authors did not record the number of records/references excluded (with reasons for exclusion) at the full‐text stage during the development of Edwards 2009 . This second review update included 513 trials. There were 23 studies awaiting classification.

Third review update (current version)

In 2021, an Information Specialist advised us of some adjustments to improve our search strategy. We reviewed the terms used to search each of the databases and included the additional use of Medical Subject Headings (MeSH) and Emtree terms in relevant databases, which were exploded or expanded appropriately to capture as many relevant articles as possible.

We added the RCT search filters developed by the Cochrane Collaboration, including the Cochrane Highly Sensitive Search Strategies for identifying randomised trials in MEDLINE (sensitivity‐maximising version) and controlled trials in Embase.

We used proximity searching and increased truncation of terms to increase search sensitivity while maintaining precision; searches of databases in title only were removed from the search strategy, and unnecessary restrictions were removed (e.g. MEDLINE searches were expanded to include all possible methods to increase questionnaire response by the removal of Part C of the original search strategy which had restricted results to known methods only).

Several changes to databases also occurred since the second update, so further changes were necessary: out‐of‐date sources were removed; C2‐SPECTR, Scientific & Technical Proceedings were replaced with Web of Science; trial register searches were expanded to include the Clinical Trials Register and the WHO International Clinical Trial Registry Platform. We also added databases to increase the breadth of the search: Global Index Medicus database from WHO (specialising in research from the global south) and Scopus.

Example search terms:

Ovid MEDLINE(R) ALL <1946 to August 13, 2021>

1 randomized controlled trial.pt.

2 controlled clinical trial.pt.

3 randomized.ab.

4 placebo.ab.

5 clinical trials as topic.sh.

6 randomly.ab.

7 trial.ti.

8 or/1‐7

9 ((questionnair* or survey* or (data adj1 collect*)) adj4 (respon* or return* or participat* or completion)).ti,ab,kf.

10 "Surveys and Questionnaires"/ or Data Collection/

11 exp Community Participation/sn [Statistics & Numerical Data]

12 9 or (10 and 11)

13 8 and 12

Notes:

Lines 1‐8 are the Cochrane Highly Sensitive Search Strategy for identifying randomised trials in MEDLINE: sensitivity‐ and precision‐maximising version.

Line 9 uses proximity searching to look for terms for questionnaires within 4 words of terms for response etc.

Lines 10 and 11 use MeSH terms to look for papers on specific subjects.

Line 12 combines the topic searches together.

Line 12 finds RCTs on the topic.

Appendix 2. Conversion of odds ratios to response rates from different baseline rates

Appendix 3. Observations from the Stakeholder Advisory Group

During the 2021‐23 update, a Stakeholder Advisory Group was recruited to comment on the work as it progressed. Members of the group were drawn from a variety of disciplines and experience, including academic and action research, community development, public health, campaigning, communications, local government and local community services. The interests of SAG members in survey and questionnaire design were heavily oriented towards social science research and, in particular, to issues such as poverty and deprivation, health and disability, race and gender. Discussions were wide‐ranging and raised considerations that could only be partly accommodated during the review update, or not at all.

There was a high level of dissatisfaction, especially amongst members working in community settings, with externally generated questionnaire surveys, as opposed to surveys generated from within fieldwork practice or service delivery. Particular points included: mistrust of motivation or intent of contractors or commissioners; researchers with poor awareness of their own personal biases or prejudicial attitudes towards target populations; and identification of ‘Questionnaire fatigue’ as potential important influences.

Strong commitment to understanding of the demography and social circumstances of target audiences and proposed collection methods was identified as key factor in achieving an inclusive sample. For social science studies, one useful mechanism against which to assess survey structure and methodology can be cross‐reference to ‘protected characteristics’ embodied in the UK’s Equality Act. A 10 th characteristic of poverty and declining social mobility could also be added to this.

In addition to the many aspects of questionnaire design covered in this review which are likely to influence response rates, additional considerations were raised against which the usefulness of data collected can be assessed. These included, for example, the issue of whether language, neurodiversity, and literacy issues were accommodated. There is evidence of further exclusion of some respondent cohorts by the move to online, paperless surveys.

Failure to record extraneous factors in research study design, such as different demographics, cultural assumptions, literacy, or language differences and the extent to which more marginalised groups respond, can undermine survey outcomes. The ability to interrogate ‘intersectionality’ in results can assist in drilling down to these underlying factors. The evidence of absence as well as evidence of presence can be significant.

There is a responsibility to make dissemination accessible, and to understand the power and impact of communication strategies.

Data and analyses

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Characteristics of excluded studies [ordered by study ID]

Characteristics of studies awaiting classification [ordered by study ID]

Differences between protocol and review

There are no differences between the protocol and the review.

Contributions of authors

Ian Roberts, Mike Clarke, and Carolyn DiGuiseppi contributed to the conception of the review. Ian Roberts, Mike Clarke, Carolyn DiGuiseppi, and Phil Edwards contributed to the design of the review. Phil Edwards and Ian Roberts contributed to the co‐ordination of the review. Ian Roberts, Mike Clarke, Carolyn DiGuiseppi, Phil Edwards, Benjamin Woolf, and Chloe Perkins contributed to the search and selection of studies for inclusion in the review, as well as the collection of data for the review. Phil Edwards and Chloe Perkins contributed to the assessment of the risk of bias in the included studies. Phil Edwards contributed to the analysis of data, assessment of the certainty in the body of evidence, and interpretation of data. All authors contributed to the writing of the review.

Sources of support

Internal sources

London School of Hygiene & Tropical Medicine, UK

Salary support for Phil Edwards

External sources

The BUPA Foundation, UK

Research grant

The Nuffield Trust, UK

Short‐Term Fellowship

NIHR, UK

NIHR Evidence Synthesis Programme Grant NIHR133238

Declarations of interest

Phil Edwards: no relevant interests; involved in 'Woolf B, Edwards P. Does advance contact with research participants increase response to questionnaires: an updated systematic review and meta‐analysis. BMC Med Res Methodol. 2021;21(1):265. doi: 10.1186/s12874‐021‐01435‐2'.

Benjamin Woolf: no relevant interests; involved in 'Woolf B, Edwards P. Does pre‐notification increase questionnaire response rates: a randomised controlled trial nested within a systematic review. BMC Med Res Methodol. 2021;21(1):259. doi: 10.1186/s12874‐021‐01462‐z'.

Chloe Perkins: no relevant interests.

Ian Roberts: no relevant interests; former Editor of Cochrane Injuries (closed in March 2023).

Carolyn DiGuiseppi: no relevant interests; former Editor of Cochrane Injuries (closed in March 2023) until November 2020.

Mike Clarke: National Institute for Health and Care Research (grant/contract); Co‐ordinating Editor of Cochrane Methodology plus other Cochrane editorial roles but he was not involved in any part of the editorial process for this review update.

New search for studies and content updated (no change to conclusions)

References

References to studies included in this review

Aadahl 2003 {published data only}

Aadahl M, Jørgensen T. The effect of conducting a lottery on questionnaire response rates: a randomised controlled trial. European Journal of Epidemiology 2003;18:941–4.

Abdulaziz 2015 {published data only}

Abdulaziz K, Brehaut J, Taljaard M, Emond M, Sirois M J, Lee J S, et al. National survey of physicians to determine the effect of unconditional incentives on response rates of physician postal surveys. BMJ OPEN 2015;5(2):e007166.

Adams 1982 {published data only}

Adams LL, Gale D. Solving the quandary between questionnaire length and response rate in educational research. Research in Higher Education 1982;17(3):231-40.

Agarwal 2016 {published data only}

Agarwal Arnav, Raad Dany, Kairouz Victor, Fudyma John, Curtis Anne B, Schunemann Holger J, et al. The effect of a monetary incentive for administrative assistants on the survey response rate: a randomized controlled trial. BMC medical research methodology 2016;16:94.

Akl 2005 {published data only}

Akl E A, Maroun N, Klocke R A, Montori V, Schünemann H J. Electronic mail was not better than postal mail for surveying residents and faculty. J Clin Epidemiol 2005;58(4):425-9.

Akl 2011 {published data only}

Akl Elie A, Gaddam Swarna, Mustafa Reem, Wilson Mark C, Symons Andrew, Grifasi Ann, et al. The effects of tracking responses and the day of mailing on physician survey response rate: three randomized trials. PloS one 2011;6(2):e16942.

Albaum 1987 {published data only}

Albaum G. Do source and anonymity affect mail survey results? Journal of the Academy of Marketing Science 1987;15(3):74-81.

Albaum 1989 {published data only}

Albaum G, Strandskov J. Participation in a mail survey of international marketers: effects of pre-contact and detailed project explanation. Journal of Global Marketing 1989;2(4):7-23.

Allen 2016 {published data only}

Allen P J, Roberts L D. The impact of academic sponsorship on Web survey dropout and item non-response. First Monday 2016;21(2):1.

Allen 2016a {published data only}

Allen P J, Roberts L D. The impact of academic sponsorship on Web survey dropout and item non-response. First Monday 2016;21(2):1.

Alutto 1970 {published data only}

Alutto JA. Some dynamics of questionnaire completion and return among professional and managerial personnel: the relative impacts of reception at work site or place of residence. Journal of Applied Psychology 1970;54(5):430-2.

Andreasen 1970 {published data only}

Andreasen AR. Personalizing mail questionnaire correspondence. Public Opinion Quarterly 1970;34:273-7.

Antoun 2017 {published data only}

Antoun C, Couper M P, Conrad F G. Effects of Mobile versus PC Web on Survey Response Quality. Public Opinion Quarterly 2017;81:280-306.

Arai 2016 {published data only}

Arai Kiichiro, Yamada Kyohei. Examining the effect of providing a pen on the response rate to a mail survey. Behaviormetrika 2016;43(2):83-101.

Arzheimer 1999 {published data only}

Arzheimer K, Klein M. The effect of material incentives on return rate, panel attrition and sample composition of a mail panel survey. International Journal of Public Opinion Research 1999;11(4):368-77.

Asch 1996 {published data only}

Asch DA. Use of a coded postcard to maintain anonymity in a highly sensitive mail survey: cost, response rates, and bias. Epidemiology 1996;7(5):550-1.

Asch 1998 {published data only}

Asch DA, Christakis NA, Ubel PA. Conducting physician mail surveys on a limited budget. A randomized trial comparing $2 bill versus $5 bill incentives. Medical Care 1998;36(1):95-9.

Ashby 2011 {published data only}

Ashby Rebecca, Turner Gwen, Cross Ben, Mitchell Natasha, Torgerson David. A randomized trial of electronic reminders showed a reduction in the time to respond to postal questionnaires. Journal of clinical epidemiology 2011;64(2):208-12.

Ashing‐Giwa 2000 {published data only}

Ashing-Giwa A, Ganz PA. Effect of timed incentives on subject participation in a study of long-term breast cancer survivors: are there ethnic differences? Journal of the National Medical Association 2000;92:528-32.

Aveyard 2001 {published data only}

Aveyard P, Manaseki S, Griffin C. The cost effectiveness of including pencils and erasers with self-completion epidemiological questionnaires. Public Health 2001;115:80-1.

Bachman 1987 {published data only}

Bachman DP. Cover letter appeals and sponsorship effects on mail survey response rates. Journal of Marketing Education 1987;9:45-51.

Bakan 2014 {published data only}

Bakan Jennifer, Chen Bing, Medeiros-Nancarrow Cheryl, Hu Jim C, Kantoff Philip W, Recklitis Christopher J. Effects of a gift certificate incentive and specialized delivery on prostate cancer survivors' response rate to a mailed survey: a randomized-controlled trial. Journal of geriatric oncology 2014;5(2):127-32.

Barker 1996 {published data only}

Barker PJ, Cooper RF. Do sexual health questions alter the public's response to lifestyle questionnaires? Journal of Epidemiology and Community Health 1996;50:688.

Barra 2016 {published data only}

Barra Mathias, Simonsen Tone Breines, Dahl Fredrik Andreas. Pre-contact by telephone increases response rates to postal questionnaires in a population of stroke patients: an open ended randomized controlled trial. BMC health services research 2016;16(1):506.

Basnov 2009 {published data only}

Basnov M, Kongsved Sm Fau - Bech Per, Bech P Fau - Hjollund Niels Henrik, Hjollund N H. Reliability of short form-36 in an Internet- and a pen-and-paper version. Inform Health Soc Care 2009;34(1):53-8.

Bauer 2004 {published data only}

Bauer JE, Rezaishiraz H, Head K, Cowell J, Bepler G, Aiken M, et al. Obtaining DNA from a geographically dispersed cohort of current and former smokers: use of mail-based mouthwash collection and monetary incentives. Nicotine & Tobacco Research 2004;6:439-46.

Bech 2009 {published data only}

Bech M, Kristensen M B. Differential response rates in postal and web-based surveys among older respondents. Survey Research Methods 2009;3(1):1-6.

Becker 2000a {published and unpublished data}

Becker H, Cookston J, Kulberg V. Mailed survey follow-ups - are postcard reminders more cost-effective than second questionnaires? Western Journal of Nursing Research 2000;22(5):642-7.

Becker 2000b {published and unpublished data}

Becker H, Cookston J, Kulberg V. Mailed survey follow-ups - are postcard reminders more cost-effective than second questionnaires? Western Journal of Nursing Research 2000;22(5):642-7.

Beebe 2005a {published data only}

Beebe TJ, Davern ME, McAlpine DD, Call KT, Rockwood TH. Increasing response rates in a survey of medicaid enrollees: the effect of a prepaid monetary incentive and mixed modes (mail and telephone). Medical Care 2005a;43(4):411-20.

Beebe 2005b {published data only}

Beebe TJ, Davern ME, McAlpine DD, Call KT, Rockwood TH. Increasing response rates in a survey of medicaid enrollees: the effect of a prepaid monetary incentive and mixed modes (mail and telephone). Medical Care 2005b;43(4):411-20.

Beebe 2005c {published data only}

Beebe TJ, Davern ME, McAlpine DD, Call KT, Rockwood TH. Increasing response rates in a survey of medicaid enrollees: the effect of a prepaid monetary incentive and mixed modes (mail and telephone). Medical Care 2005c;43(4):411-20.

Beebe 2005d {published data only}

Beebe TJ, Davern ME, McAlpine DD, Call KT, Rockwood TH. Increasing response rates in a survey of medicaid enrollees: the effect of a prepaid monetary incentive and mixed modes (mail and telephone). Medical Care 2005d;43(4):411-20.

Beebe 2005e {published data only}

Beebe TJ, Davern ME, McAlpine DD, Call KT, Rockwood TH. Increasing response rates in a survey of medicaid enrollees: the effect of a prepaid monetary incentive and mixed modes (mail and telephone). Medical Care 2005e;43(4):411-20.

Beebe 2005f {published data only}

Beebe TJ, Davern ME, McAlpine DD, Call KT, Rockwood TH. Increasing response rates in a survey of medicaid enrollees: the effect of a prepaid monetary incentive and mixed modes (mail and telephone). Medical Care 2005f;43(4):411-20.

Beebe 2007 {published data only}

Beebe TJ, Stoner SM, Anderson KJ, Williams AR. Selected questionnaire size and color combinations were significantly related to mailed survey response rates. Journal of Clinical Epidemiology 2007;60:1184-9.

Beebe 2007a {published data only}

Beebe Timothy J, Locke G Richard 3rd, Barnes Sunni A, Davern Michael E, Anderson Kari J. Mixing web and mail methods in a survey of physicians. Health services research 2007;42(3 Pt 1):1219-34.

Beebe 2010 {published data only}

Beebe Timothy J, Rey Enrique, Ziegenfuss Jeanette Y, Jenkins Sarah, Lackore Kandace, Talley Nicholas J, et al. Shortening a survey and using alternative forms of prenotification: impact on response rate and quality. BMC medical research methodology 2010;10:50.

Beebe 2018 {published data only}

Beebe Timothy J, Jacobson Robert M, Jenkins Sarah M, Lackore Kandace A, Rutten Lila J Finney. Testing the Impact of Mixed-Mode Designs (Mail and Web) and Multiple Contact Attempts within Mode (Mail or Web) on Clinician Survey Response. Health services research 2018;53 Suppl 1(g2l, 0053006):3070-83.

Bell 2004 {published data only}

Bell LS, Butler TL, Herring RP, Yancey AK, Fraser GE. Recruiting blacks to the adventist health study: do follow-up phone calls increase response rates? Annals of Epidemiology 2005;15(9):667–72.

Bell 2016 {published data only}

Bell K, Clark L, Fairhurst C, Mitchell N, Lenaghan E, Blacklock J, et al. Enclosing a pen reduced time to response to questionnaire mailings. JOURNAL OF CLINICAL EPIDEMIOLOGY 2016;74:144-50.

Bellizzi 1986 {published data only}

Bellizzi JA, Hite RE. Face-to-face advance contact and monetary incentives: effects on mail survey return rates, response differences, and survey costs. Journal of Business Research 1986;14:99-106.

Berdie 1973 {published data only}

Berdie DR. Questionnaire length and response rate. Journal of Applied Psychology 1973;58(2):278-80.

Bergen 1957 {published data only}

Bergen AV, Spitz JC. The introduction of a written survey [De introductie van een schriftelijke enquete]. Nederlandsch Tijdschrift voor Psychologie 1957;12:68-96.

Bergeson 2013 {published data only}

Bergeson SC, Gray J, Ehrmantraut LA, Laibson T, Hays RD. Comparing Web-based with Mail Survey Administration of the Consumer Assessment of Healthcare Providers and Systems (CAHPS R) Clinician and Group Survey. Primary Health Care 2013;15(3):1000132.

Berk 1993 {published data only}

Berk ML, Edwards WS, Gay NL. The use of a prepaid incentive to convert non responders on a survey of physicians. Evaluation & the Health Professions 1993;16:239-45.

Berry 1987 {published data only}

Berry S. Physician response to a mailed survey. An experiment in timing of payment. Public Opinion Quarterly 1987;51:102-14.

Beydoun 2006 {published data only}

Beydoun H, Saftlas AF, Harland K, Triche E. Combining conditional and unconditional recruitment incentives could facilitate telephone tracing in surveys of postpartum women. Journal of Clinical Epidemiology 2006;59:732–8.

Bhandari 2003 {published data only}

Bhandari M, Swiontkowski MF, Shankardass K, Sprague S, Schemitsch EH, Guyatt GH. A randomized trial of opinion leader endorsement in a survey of orthopaedic surgeons: effect on primary response rates. International Journal of Epidemiology 2003;32:634–6.

Biner 1988 {published data only}

Biner PM. Effects of cover letter appeal and monetary incentives on survey response: a reactance theory application. Basic and Applied Social Psychology 1988;9(2):99-106.

Biner 1990 {published data only}

Biner PM, Barton DL. Justifying the enclosure of monetary incentives in mail survey cover letters. Psychology & Marketing 1990;7(3):153-62.

Biner 1994 {published data only}

Biner PM, Kidd HJ. The interactive effects of monetary incentive justification and questionnaire length on mail survey response rates. Psychology & Marketing 1994;11(5):483-92.

Birnholtz 2004 {published data only}

Birnholtz JP, Horn DB, Finholt TA, Bae SJ. The effect of cash, electronic, and paper gift certificates as respondent incentives for a web based survey of technologically sophisticated respondents. Social Science Computer Review 2004;22:355-62.

Bjertnaes 2012 {published data only}

Bjertnaes O A, Iversen H H. User-experience surveys with maternity services: a randomized comparison of two data collection models. INTERNATIONAL JOURNAL FOR QUALITY IN HEALTH CARE 2012;24(4):433-8.

Bjertnaes 2018 {published data only}

Bjertnaes Oyvind, Iversen Hilde Hestad, Skrivarhaug Torild. A randomized comparison of three data collection models for the measurement of parent experiences with diabetes outpatient care. BMC Medical Research Methodology 2018;18(1):N.PAG.

Blass 1981 {published data only}

Blass T, Leichtman SR, Brown RA. The effect of perceived consensus and implied threat upon responses to mail surveys. Journal of Social Psychology 1981;113:213-6.

Blass‐Wilhems 1982 {published data only}

Blass-Wilhelms W. Influence of 'real' postage stamp versus stamp 'postage paid' on return rate of response cards [Der EinfluB der Frankierungsart auf Rucklauf von Antwortkarten]. Zeitschrift fur Soziologie 1982;11(1):64-8.

Blomberg 1996 {published data only}

Blomberg J, Sandell R. Does a material incentive affect response on a psychotherapy follow-up questionnaire? Psychotherapy Research 1996;6(3):155-63.

Blumenberg 2019 {published data only}

Blumenberg C, Menezes A M B, Goncalves H, Assuncao M C F, Wehrmeister F C, Barros F C, et al. The role of questionnaire length and reminders frequency on response rates to a web-based epidemiologic study: a randomised trial. INTERNATIONAL JOURNAL OF SOCIAL RESEARCH METHODOLOGY 2019;22(6):625-35.

Blythe 1986 {published data only}

Blythe BJ. Increasing mailed survey responses with a lottery. Social Work Research Abstracts 1986;22:18-9.

Bolt 2014 {published data only}

Bolt E E, Heide A, Onwuteaka-Philipsen B D. Reducing questionnaire length did not improve physician response rate: a randomized trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2014;67(4):477-81.

Bond 2020 {published data only}

Bond D M, Hammond J, Shand A W, Nassar N. Comparing a Mobile Phone Automated System With a Paper and Email Data Collection System: substudy within a Randomized Controlled Trial. JMIR Mhealth Uhealth 2020;8(8):e15284.

Bonevski 2011 {published data only}

Bonevski B, Magin P, Horton G, Foster M, Girgis A. Response rates in GP surveys Trialling two recruitment strategies. AUSTRALIAN FAMILY PHYSICIAN 2011;40(6):427-30.

Bonevski 2011a {published data only}

Bonevski B, Magin P, Horton G, Foster M, Girgis A. Response rates in GP surveys Trialling two recruitment strategies. AUSTRALIAN FAMILY PHYSICIAN 2011;40(6):427-30.

Boser 1990 {published data only}

Boser JA. Surveying alumni by mail: effect of booklet/folder questionnaire format and style of type on response rate. Research in Higher Education 1990;31(2):149-59.

Bosnjak 2003 {published data only}

Bosnjak M, Tuten TL. Prepaid and promised incentives in web surveys: an experiment. Social Science Computer Review 2003;21:208-17.

Boulianne 2012 {published data only}

Boulianne Shelley. Examining the Gender Effects of Different Incentive Amounts in a Web Survey. FIELD METHODS 2012;25(1):91-104.

Boyd 2015 {published data only}

Boyd A, Tilling K, Cornish R, Davies A, Humphries K, Macleod J. Professionally designed information materials and telephone reminders improved consent response rates: evidence from an RCT nested within a cohort study. JOURNAL OF CLINICAL EPIDEMIOLOGY 2015;68(8):877-87.

Boyle 2012 {published data only}

Boyle T, Heyworth J, Landrigan J, Mina R, Fritschi L. The Effect of Lottery Scratch Tickets and Donation Offers on Response Fraction: A Study and Meta-Analysis. FIELD METHODS 2012;24(1):112-32.

Bradshaw 2020 {published data only}

Bradshaw L E, Montgomery A A, Williams H C, Chalmers J R, Haines R H. Two-by-two factorial randomised study within a trial (SWAT) to evaluate strategies for follow-up in a randomised prevention trial. TRIALS 2020;21(1):529.

Bray 2017 {published data only}

Bray I, Noble S, Robinson R, Molloy L, Tilling K. Mode of delivery affected questionnaire response rates in a birth cohort study. JOURNAL OF CLINICAL EPIDEMIOLOGY 2017;81:64-71.

Bredart 2002 {published data only}

Bredart A, Razavi D, Robertson C, Brignone S, Fonzo D, Petit J-Y, et al. Timing of patient satisfaction assessment: effect on questionnaire acceptability, completeness of data, reliability and variability of scores. Patient Education and Counseling 2002;46:131-6.

Breen 2010 {published data only}

Breen C L, Shakeshaft A P, Doran C M, Sanson-Fisher R W, Mattick R P. Cost-effectiveness of follow-up contact for a postal survey: a randomised controlled trial. AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH 2010;34(5):508-12.

Brehaut 2006 {published data only}

Brehaut JC, Graham ID, Visentin L, Stiell IG. Print format and sender recognition were related to survey completion rate. Journal of Clinical Epidemiology 2006;59:635–41.

Brems 2006 {published data only}

Brems C, Johnson ME, Warner T. Survey return rates as a function of priority versus first-class mailing. Psychological Reports 2006;99:496-501.

Brennan 1991 {published data only}

Brennan M, Hoek J, Astridge C. The effects of monetary incentives on the response rate and cost-effectiveness of a mail survey. Journal of the Market Research Society 1991;33:229-41.

Brennan 1992a {published data only}

Brennan M. The effect of a monetary incentive on mail survey response rates. Journal of the Market Research Society 1992;34(2):173-7.

Brennan 1992b {published data only}

Brennan M. The effect of a monetary incentive on mail survey response rates. Journal of the Market Research Society 1992;34(2):173-7.

Brennan 1992c {published data only}

Brennan M. The effect of a monetary incentive on mail survey response rates. Journal of the Market Research Society 1992;34(2):173-7.

Brennan 1993a {published data only}

Brennan M, Seymour P, Gendall P. The effectiveness of monetary incentives in mail surveys: further data. Marketing Bulletin 1993;4:43-52.

Brennan 1993b {published data only}

Brennan M, Seymour P, Gendall P. The effectiveness of monetary incentives in mail surveys: further data. Marketing Bulletin 1993;4:43-52.

Brennan 2009 {published data only}

Brennan Mike, Charbonneau Jan. Improving Mail Survey Response Rates Using Chocolate and Replacement Questionnaires. The Public Opinion Quarterly 2009;73(2):368-78.

Bright 2002 {published data only}

Bright KD, Smith PM. The use of incentives to affect response rates for a mail survey of US marina decision makers. Forest Products Journal 2002;52(10):26-9.

Brook 1978 {published data only}

Brook LL. The effect of different postage combinations on response levels and speed of reply. Journal of the Market Research Society 1978;20:238-44.

Brookes 2018a {published data only}

Brookes Sara T, Chalmers Katy A, Avery Kerry N L, Coulman Karen, Blazeby Jane M, group Romio study. Impact of question order on prioritisation of outcomes in the development of a core outcome set: a randomised controlled trial. Trials 2018;19(1):66.

Brookes 2018b {published data only}

Brookes Sara T, Chalmers Katy A, Avery Kerry N L, Coulman Karen, Blazeby Jane M, group Romio study. Impact of question order on prioritisation of outcomes in the development of a core outcome set: a randomised controlled trial. Trials 2018;19(1):66.

Brown 1965 {published data only}

Brown ML. Use of a postcard query in mail surveys. Public Opinion Quarterly 1965;29:635-637.

Brown 1975 {published data only}

Brown GH. Randomised inquiry vs conventional questionnaire method in estimating drug usage rates through mail surveys (Technical Report). Human Resources Research Organisation (HumRRO). US Army Research Institute for the behavioural & Social Sciences, Virginia 1975.

Bruce 2000 {published data only}

Bruce T, Salkeld G, Short L, Solomon M, Ward J. A randomised trial of telephone versus postcard prompts to enhance response rate in a phased population-based study about community preferences. Australian and New Zealand Journal of Public Health 2000;24(4):456-7.

Brøgger 2007 {published data only}

Brøgger J, Nystad W, Cappelen I, Bakke P. No increase in response rate by adding a web response option to a postal population survey: A randomized trial. Jornal of Medical Internet Research 2007;9(5):e40.

Buchman 1982 {published data only}

Buchman TA, Tracy JA. Obtaining responses to sensitive questions: conventional questionnaire versus randomized response technique. Journal of Accounting Research 1982;20(1):263-271.

Burgess 2012 {published data only}

Burgess Caroline, Nicholas Jennifer, Gulliford Martin. Impact of an electronic, computer-delivered questionnaire, with or without postal reminders, on survey response rate in primary care. Journal of Epidemiology and Community Health 2012;66(7):663-4.

Burns 1980 {published data only}

Burns AC, Hair JF. An analysis of mail survey responses from a commercial sample. American Institute Decision Science 1980;1:227-9.

Buttle 1997 {published data only}

Buttle F, Thomas G. Questionnaire colour and mail survey response rate. Journal of the Market Research Society 1997;39(4):625-6.

Cabana 2000 {published data only}

Cabana MD, Becher O, Rubin HR, Freed GL. Effect of repeated presentations of a study logo on physician survey response rate. Pediatric Research 2000;47(4):p843.

Campbell 1990 {published data only}

Campbell MJ, Waters WE. Does anonymity increase response rate in postal questionnaire surveys about sensitive subjects? A randomised trial. Journal of Epidemiology and Community Health 1990;44:75-76.

Camunas 1990 {published data only}

Camunas C, Alward RR, Vecchione E. Survey response rates to a professional association mail questionnaire. Journal of the New York State Nurses Association 1990;21(3):7-9.

Carling 2004 {published data only}

Carling C. International Questionnaire Postal Response Rate: An experiment comparing no return postage to provision of International Postage Vouchers - "Coupon-Reponse International". BMC Health Services Research 2004;4(16):1-3.

Carpenter 1974 {published data only}

Carpenter EH. Personalizing mail surveys: a replication and reassessment. Public Opinion Quarterly 1974;38:614-620.

Carpenter 1977 {published data only}

Carpenter EH. Evaluation of mail questionnaires for obtaining data from more than one respondent in a household. Rural Sociology 1977;42(2):250-9.

Cartwright 1986 {published data only}

Cartwright A. Some experiments with factors that might affect the response of mothers to a postal questionnaire. Statistics in Medicine 1986;5:607-17.

Cartwright 1987 {published data only}

Cartwright A, Smith C. Identifying a sample of elderly people by a postal screen. Age & Ageing 1987;16:119-22.

Chan 2003 {published data only}

Chan TMT, Tse SHM, Day MC, Tong ETF, Suen LKP. Randomized trial of use of incentive to increase the response rate to a mailed survey. Asian Journal of Nursing Studies 2003;6(3):36-43.

Chan 2018 {published data only}

Chan R C H, Mak W W S, Pang I H Y, Wong S Y S, Tang W K, Lau J T F, et al. Utility and Cost-effectiveness of Motivational Messaging to Increase Survey Response in Physicians: A Randomized Controlled Trial. FIELD METHODS 2018;30(1):37-55.

Chebat 1991 {published data only}

Chebat J-C, Picard J. Does prenotification increase response rates in mail surveys? A self-perception approach. Journal of Social Psychology 1991;13(4):477-81.

Chen 1984 {published data only}

Chen C. Questionnaire length, salience and researchers' authority, and follow-up: the effect on response rates for postal questionnaires. Chinese Journal of Psychology 1984;26(2):77-84.

Childers 1979 {published data only}

Childers TL, Skinner SJ. Gaining respondent cooperation in mail surveys through prior commitment. Public Opinion Quarterly 1979;43:558-61.

Childers 1980a {published data only}

Childers TL, Pride WM, Ferrell OC. A reassessment of the effects of appeals on response to mail surveys. Journal of Marketing Research 1980;17:365-70.

Childers 1980b {published data only}

Childers TL, Pride WM, Ferrell OC. A reassessment of the effects of appeals on response to mail surveys. Journal of Marketing Research 1980;17:365-70.

Childers 1985 {published data only}

Childers TL, Skinner SJ. Theoretical and empirical issues in the identification of survey respondents. Journal of the Market Research Society 1985;27(1):39-53.

Childers TL 1979 {published data only}

Childers TL, Ferrell OC. Response rates and perceived questionnaire length in mail surveys. Journal of Marketing Research 1979;16:429-31.

Choi 1990 {published data only}

Choi BC, Pak AW, Purdham JT. Effects of mailing strategies on response rate, response time, and cost in a questionnaire study among nurses. Epidemiology 1990;1(1):72-4.

Choudhury 2012 {published data only}

Choudhury Yasmin, Hussain Iqbal, Parsons Suzanne, Rahman Anisur, Eldridge Sandra, Underwood Martin. Methodological challenges and approaches to improving response rates in population surveys in areas of extreme deprivation. Primary health care research & development 2012;13(3):211-8.

Christensen 2019 {published data only}

Christensen Anne Illemann, Lynn Peter, Tolstrup Janne Schurmann. Can targeted cover letters improve participation in health surveys? Results from a randomized controlled trial. BMC medical research methodology 2019;19(1):151.

Christie 1985 {unpublished data only}

Christie SC. An analysis of three different treatments on the response rate of a mail survey. Student Research Report, Department of Marketing, Massey University 1985.

Church 2004 {published data only}

Church TR, Yeazel MW, Jones RM, Kochevar LK, Watt GD, Mongin SJ, et al. A randomized trial of direct mailing of fecal occult blood tests to increase colorectal cancer screening. Journal of the National Cancer Institute 2004;96(10):770-80.

Clark 2001 {published data only}

Clark TJ, Khan KS, Gupta JK. Provision of pen along with questionnaire does not increase the response rate to a postal survey: a randomised controlled trial. Journal of Epidemiology and Community Health 2001;55:595-6.

Clark 2011 {published data only}

Clark Melissa, Rogers Michelle, Foster Andrew, Dvorchak Faye, Saadeh Frances, Weaver Jessica, et al. A randomized trial of the impact of survey design characteristics on response rates among nursing home providers. Evaluation & the health professions 2011;34(4):464-86.

Clark 2015 {published data only}

Clark Laura, Ronaldson Sarah, Dyson Lisa, Hewitt Catherine, Torgerson David, Adamson Joy. Electronic prompts significantly increase response rates to postal questionnaires: a randomized trial within a randomized trial and meta-analysis. Journal of clinical epidemiology 2015;68(12):1446-50.

Clarke 1998 {published data only}

Clarke R, Breeze E, Sherliker P, Shipley M, Youngman L. Design, objectives, and lessons from a pilot 25 year follow up re-survey of survivors in the Whitehall study of London civil servants. Journal of Epidemiology and Community Health 1998;52:364-9.

Clarke 2007 {published data only}

Clarke M, Clarke L, Clarke T. Yes Sir, no Sir, not much difference Sir. Journal of the Royal Society of Medicine 2007;100(12):571-2.

Clark TJ 2001 {published data only}

Clark TJ, Khan KS, Gupta JK. Effect of paper quality on the response rate to a postal survey: a randomised controlled trial. BMC Medical Research Methodology 2001;1:12.

Clausen 1947 {published data only}

Clausen JA, Ford RN. Controlling bias in mail questionnaires. Journal of the American Statistical Association 1947;42(240):497-511.

Claycomb 2000 {published data only}

Claycomb C, Porter SS, Martin CL. Riding the wave: response rates and the effects of time intervals between successive mail survey follow-up efforts. Journal of Business Research 2000;48:157-62.

Cleopas 2006 {published data only}

Cleopas A, Kolly V, Perneger TV. Longer response scales improved the acceptability and performance of the Nottingham Health Profile. Journal of Clinical Epidemiology 2006;59(11):1183-90.

Coast 2006 {published data only}

Coast Joanna, Flynn Terry N, Salisbury Chris, Louviere Jordan, Peters Tim J. Maximising Responses to Discrete Choice Experiments: A Randomised Trial. Applied Health Economics and Health Policy 2006;5(4):249-60.

Cobanoglu 2001 {published data only}

Cobanoglu Cihan, Moreo Patrick J, Warde Bill. A Comparison of Mail, Fax and Web-Based Survey Methods. International Journal of Market Research 2001;43(4):1-15.

Cobanoglu 2003 {published data only}

Cobanoglu C, Cobanoglu N. The effect of incentives in websurveys: application and ethical considerations. International Journal of Market Research 2003;45(4):475-88.

Cochrane 2020 {published data only}

Cochrane Ann, Welch Charlie, Fairhurst Caroline, Cockayne Sarah, Torgerson David J, Group Otis Study. An evaluation of a personalised text message reminder compared to a standard text message on postal questionnaire response rates: an embedded randomised controlled trial. F1000Research 2020;9(101594320):154.

Cockayne 2005 {published data only}

Cockayne S, Torgerson DJ. A randomised controlled trial to assess the effectiveness of offering study results as an incentive to increase response rates to postal questionnaires. BMC Medical Research Methodology 2005;5(34):1-5.

Cohen 2019 {published data only}

Cohen Andrew J, Washington Sam, Butler Christi, Kamal Puneet, Patino German, Tresh Anas, et al. Altruistic donation to improve survey responses: a global randomized trial. BMC research notes 2019;12(1):113.

Collins 2000 {published data only}

Collins RL, Ellickson PL, Hays RD, McCaffrey DF. Effects on incentive size and timing on response rates to a follow-up wave of a longitudinal mailed survey. Evaluation Review 2000;24(4):347-63.

Conner 2017 {published data only}

Conner M, Sandberg T, Nekitsing C, Hutter R, Wood C, Jackson C, et al. Varying cognitive targets and response rates to enhance the question-behaviour effect: An 8-arm Randomized Controlled Trial on influenza vaccination uptake. SOCIAL SCIENCE & MEDICINE 2017;180:135-42.

Converse 2008 {published data only}

Converse Patrick D, Wolfe Edward W, Xiaoting Huang, Oswald Frederick L. Response Rates for Mixed-Mode Surveys Using Mail and E-mail/Web. American Journal of Evaluation 2008;29(1):99-107.

Cook 2016 {published data only}

Cook David A, Wittich Christopher M, Daniels Wendlyn L, West Colin P, Harris Ann M, Beebe Timothy J. Incentive and Reminder Strategies to Improve Response Rate for Internet-Based Physician Surveys: A Randomized Experiment. Journal of medical Internet research 2016;18(9):e244.

Corcoran 1985 {published data only}

Corcoran KJ. Enhancing the response rate in survey research. Social Work Research & Abstracts 1985;21:2.

Coryn 2020 {published data only}

Coryn Chris L S, Becho Lyssa W, Westine Carl D, Mateu Pedro F, Abu-Obaid Ruqayyah N, Hobson Kristin A, et al. Material incentives and other potential factors associated with response rates to internet surveys of American Evaluation Association members: Findings from a randomized experiment. American Journal of Evaluation 2020;41(2):277-96.

Cosgrove 2018 {published data only}

Cosgrove John A. Using a Small Cash Incentive to Increase Survey Response. Administration and policy in mental health 2018;45(5):813-9.

Cotterill 2017 {published data only}

Cotterill S, Howells K, Rhodes S, Bower P. The effect of using social pressure in cover letters to improve retention in a longitudinal health study: an embedded randomised controlled retention trial. TRIALS 2017;18:341.

Cottrell 2015 {published data only}

Cottrell E, Roddy E, Rathod T, Thomas E, Porcheret M, Foster N E. Maximising response from GPs to questionnaire surveys: do length or incentives make a difference? BMC MEDICAL RESEARCH METHODOLOGY 2015;15:3.

Coughlin 2011 {published data only}

Coughlin Steven, Aliaga Pablo, Barth Shannon, Eber Stephanie, Maillard Jessica, Mahan Clare, et al. The Effectiveness of a Monetary Incentive on Response Rates in a Survey of Recent U.S. Veterans. Survey practice 2011;4:1-8.

Cox 1974 {published data only}

Cox EP, Anderson T, Fulcher DG. Reappraising mail survey response rates. Journal of Marketing Research 1974;11:413-7.

Crittenden 1985 {published data only}

Crittenden WF, Crittenden VL, Hawes JM. Examining the effects of questionnaire color and print font on mail survey response rates. Akron Business and Economic Review 1985;16(4):31-56.

Cunningham‐Burley 2020 {published data only}

Cunningham-Burley Rachel, Roche Jenny, Fairhurst Caroline, Cockayne Sarah, Hewitt Catherine, Iles-Smith Heather, et al. Enclosing a pen to improve response rate to postal questionnaire: an embedded randomised controlled trial. F1000Research 2020;9(101594320):577.

Cureton 2021 {published data only}

Cureton L, Marian I R, Barber V S, Parker A, Torgerson D J, Hopewell S. Randomised study within a trial (SWAT) to evaluate personalised versus standard text message prompts for increasing trial participant response to postal questionnaires (PROMPTS). TRIALS 2021;22(1):502.

Cycyota 2002 {published data only}

Cycyota C, Harrison DA. Enhancing survey response rates at the executive level: Are employee- or consumer-level techniques effective? Journal of Management 2002;28(2):151-76.

Danko 2019 {published data only}

Danko Kristin J, Dahabreh Issa J, Ivers Noah M, Moher David, Grimshaw Jeremy M. Contacting authors by telephone increased response proportions compared with emailing: results of a randomized study. Journal of clinical epidemiology 2019;115(jce, 8801383):150-9.

Deehan 1997 {published data only}

Deehan A, Templeton L, Taylor C, Drummond C, Strang J. The effect of cash and other financial inducements on the response rate of general practitioners in a national postal study. British Journal of General Practice 1997;47:87-90.

Delnevo 2004 {published data only}

Delnevo CD, Abatemarco DJ, Steinberg MB. Physician response rates to a mail survey by specialty and timing of incentive. American Journal of Preventive Medicine 2004;26(3):234-6.

Delnevo 2021 {published data only}

Delnevo CD, Singh B. The effect of a web-push survey on physician survey responses rates: a randomized experiment. Survey practice 2021;14(1):10.29115/sp-2021-0001.

Del Valle 1997 {published data only}

Del Valle ML, Morgenstern H, Rogstad TL, Albright C, Vickrey BG. A randomised trial of the impact of certified mail on response rate to a physician survey, and a cost-effectiveness analysis. Evaluation & the Health Professions 1997;20(4):389-406.

Denton 1988 {published data only}

Denton J, Tsai C-Y, Chevrette P. Effects on survey responses of subjects, incentives, and multiple mailings. Journal of Experimental Education 1988;56:77-82.

Denton 1991 {published data only}

Denton JJ, Tsai C-Y. Two investigations into the influence of incentives and subject characteristics on mail survey responses in teacher education. Journal of Experimental Education 1991;59:352-66.

Deutskens 2004a {published data only}

Deutskens E, Ruyter KD, Wetzels M, Oosterveld P. Response rate and response quality of internet-based surveys: an experimental study. Marketing Letters 2004;15(1):21-36.

Deutskens 2004b {published data only}

Deutskens E, Ruyter KD, Wetzels M, Oosterveld P. Response rate and response quality of internet-based surveys: an experimental study. Marketing Letters 2004;15(1):21-36.

Dillman 1974a {published data only}

Dillman DA, Frey JH. Contribution of personalization to mail questionnaire response as an element of a previously tested method. Journal of Applied Psychology 1974;59(3):297-301.

Dillman 1974b {published data only}

Dillman DA, Frey JH. Contribution of personalization to mail questionnaire response as an element of a previously tested method. Journal of Applied Psychology 1974;59(3):297-301.

Dillman 1993 {published data only}

Dillman DA, Sinclair MD, Clark JR. Effects of questionnaire length, respondent-friendly design, and a difficult question on response rates for occupant-addressed census mail surveys. Public Opinion Quarterly 1993;57(3):289-304.

Dillman 1996 {published data only}

Dillman DA, Singer E, Clark JR, Treat JB. Effects of benefits appeals, mandatory appeals, and variations in statements of confidentiality on completion rates for census questionnaires. Public Opinion Quarterly 1996;60:376-89.

Dinglas 2015 {published data only}

Dinglas V D, Huang M, Sepulveda K A, Pinedo M, Hopkins R O, Colantuoni E, et al. Personalized contact strategies and predictors of time to survey completion: Analysis of two sequential randomized trials Study design. BMC Medical Research Methodology 2015;15(1):5.

Dirmaier 2007 {published data only}

Dirmaier J, Harfst T, Koch U, Schulz H. Incentives increased return rates but did not influence partial nonresponse or treatment outcome in a randomized trial. Journal of Clinical Epidemiology 2007;60:1263-70.

Dodd 1987 {published data only}

Dodd DK, Markwiese BJ. Survey response rate as a function of personalized signature on cover letter. Journal of Social Psychology 1987;127(1):97-8.

Doerfling 2010 {published data only}

Doerfling Paul, Kopec Jacek A, Liang Matthew H, Esdaile John M. The effect of cash lottery on response rates to an online health survey among members of the Canadian Association of Retired Persons: a randomized experiment. Canadian journal of public health = Revue canadienne de sante publique 2010;101(3):251-4.

Dommeyer 1980a {unpublished data only}

Dommeyer CJ. Experimentation on threatening appeals in the follow-up letters of a mail survey. Doctoral Dissertation 1980.

Dommeyer 1980b {unpublished data only}

Dommeyer CJ. Experimentation on threatening appeals in the follow-up letters of a mail survey. Doctoral Dissertation 1980.

Dommeyer 1985 {published data only}

Dommeyer CJ. Does response to an offer of mail survey results interact with questionnaire interest? Journal of the Market Research Society 1985;27(1):27-38.

Dommeyer 1987 {published data only}

Dommeyer CJ. The effects of negative cover letter appeals on mail survey response. Journal of the Market Research Society 1987;29(4):445-51.

Dommeyer 1988 {published data only}

Dommeyer CJ. How form of the monetary incentive affects mail survey response. Journal of the Market Research Society 1988;30(3):379-85.

Dommeyer 1989 {published data only}

Dommeyer CJ. Offering mail survey results in a lift letter. Journal of the Market Research Society 1989;31(3):399-408.

Dommeyer 1991 {published data only}

Dommeyer CJ, Elganayan D, Umans C. Increasing mail survey response with an envelope teaser. Journal of the Market Research Society 1991;33(2):137-40.

Dommeyer 1996 {published data only}

Dommeyer CJ, Ruggiero LA. The effects of a photograph on mail survey response. Marketing Bulletin 1996;7:51-7.

Dommeyer 2004 {published data only}

Dommeyer CJ, Baum P, Hanna RW, Chapman KS. Gathering faculty teaching evaluations by in-class and online surveys: their effects on response rates and evaluations. Assessment & Evaluation in Higher Education 2004;29(5):611-23.

Donaldson 1999 {published data only}

Donaldson GW, Moinpour CM, Bush NE, Chapko M, Jocom J, Siadak M, et al. Physician participation in research surveys: a randomized study of inducements to return mailed research questionnaires. Evaluation & the Health Professions 1999;22(4):427-41.

Doob 1971a {published data only}

Doob A, Zabrack M. The effect of freedom-threatening instructions and monetary inducement on compliance. Canadian Journal of Behavioural Science 1971;3(4):408-12.

Doob 1971b {published data only}

Doob A, Zabrack M. The effect of freedom-threatening instructions and monetary inducement on compliance. Canadian Journal of Behavioural Science 1971;3(4):408-12.

Doob 1971c {published data only}

Doob A, Zabrack M. The effect of freedom-threatening instructions and monetary inducement on compliance. Canadian Journal of Behavioural Science 1971;3(4):408-12.

Doob 1973 {published data only}

Doob AN, Freedman JL, Carlsmith JM. Effects of sponsor and prepayment on compliance with a mailed request. Journal of Applied Psychology 1973;57:346-7.

Doody 2003a {published data only}

Doody MM, Sigurdson AS, Kampa D, Chimes K, Alexander BH, Ron E, et al. Randomized trial of financial incentives and delivery methods for improving response to a mailed questionnaire. American Journal of Epidemiology 2003;157(7):643-51.

Doody 2003b {published data only}

Doody MM, Sigurdson AS, Kampa D, Chimes K, Alexander BH, Ron E, et al. Randomized trial of financial incentives and delivery methods for improving response to a mailed questionnaire. American Journal of Epidemiology 2003;157(7):643-51.

Dorman 1997 {unpublished data only}

Dorman PJ, Slattery JM, Farrell B, Dennis MS, Sandercock PAG, the United Kingdom Collaborators in the International Stroke Trial. A randomised comparison of the EuroQol and SF-36 after stroke. BMJ 1997;315:461.

Downes‐Le Guin 2002 {published data only}

Downes-Le Guin T, Janowitz P, Stone R, Khorram S. Use of pre-incentives in an Internet survey. Journal of Online Research 2002;www.ijor.org/ijor_archives/articles/Use_of_pre-incentives_in_an_internet_survey.pdf.

Drummond 2008 {published data only}

Drummond FJ, Sharp L, Carsin AE, Kelleher T, Comber H. Questionnaire order significantly increased response to a postal survey sent to primary care physicians. Journal of Clinical Epidemiology 2008;61:177-85.

Drummond 2014 {published data only}

Drummond F J, O'Leary E, O'Neill C, Burns R, Sharp L. "Bird in the hand" cash was more effective than prize draws in increasing physician questionnaire response. JOURNAL OF CLINICAL EPIDEMIOLOGY 2014;67(2):228-31.

Duffy 2001 {published data only}

Duffy DL, Martin NG. Increasing the response rate to a mailed questionnaire by including more stamps on the return envelope: a cotwin control study. Twin Research 2001;4(2):71-2.

Duhan 1990 {published data only}

Duhan DF, Wilson RD. Prenotification and industrial survey responses. Industrial Marketing Management 1990;19:95-105.

Dunn 2003 {published data only}

Dunn KM, Jordan K, Croft PR. Does questionnaire structure influence response in postal surveys? Journal of Clinical Epidemiology 2003;56:10–6.

Dykema 2011 {published data only}

Dykema Jennifer, Stevenson John, Day Brendan, Sellers Sherrill L, Bonham Vence L. Effects of incentives and prenotification on response rates and costs in a national web survey of physicians. Evaluation & the health professions 2011;34(4):434-47.

Dykema 2012 {published data only}

Dykema J, Stevenson J, Kniss C, Kvale K, Gonzalez K, Cautley E. Use of Monetary and Nonmonetary Incentives to Increase Response Rates Among African Americans in the Wisconsin Pregnancy Risk Assessment Monitoring System. MATERNAL AND CHILD HEALTH JOURNAL 2012;16(4):785-91.

Dykema 2013 {published data only}

Dykema J, Stevenson J, Klein L, Kim Y, Day B. Effects of E-Mailed Versus Mailed Invitations and Incentives on Response Rates, Data Quality, and Costs in a Web Survey of University Faculty. SOCIAL SCIENCE COMPUTER REVIEW 2013;31(3):359-70.

Dykema 2015a {published data only}

Dykema J, Jaques K, Cyffka K, Assad N, Hammers R G, Elver K, et al. EFFECTS OF SEQUENTIAL PREPAID INCENTIVES AND ENVELOPE MESSAGING IN MAIL SURVEYS. PUBLIC OPINION QUARTERLY 2015;79(4):906-31.

Dykema 2015b {published data only}

Dykema J, Jaques K, Cyffka K, Assad N, Hammers R G, Elver K, et al. EFFECTS OF SEQUENTIAL PREPAID INCENTIVES AND ENVELOPE MESSAGING IN MAIL SURVEYS. PUBLIC OPINION QUARTERLY 2015;79(4):906-31.

Dykema 2021 {published data only}

Dykema Jennifer, Stevenson John, Assad Nadia, Kniss Chad, Taylor Catherine A. Effects of Sequential Prepaid Incentives on Response Rates, Data Quality, Sample Representativeness, and Costs in a Mail Survey of Physicians. Evaluation & the health professions 2021;44(3):235-44.

Eaker 1998 {published data only}

Eaker S, Bergstrom R, Bergstrom A, Hans-Olov A, Nyren O. Response rate to mailed epidemiologic questionnaires: a population-based randomized trial of variations in design and mailing routines. Americal Journal of Epidemiology 1998;147(1):74-82.

Easton 1997 {published data only}

Easton AN, Price JH, Telljohann SK, Boehm K. An informational versus monetary incentive in increasing physicians' response rates. Psychological Reports 1997;81:968-70.

Edelman 2013 {published data only}

Edelman L S, Yang R M, Guymon M, Olson L M. Survey Methods and Response Rates Among Rural Community Dwelling Older Adults. NURSING RESEARCH 2013;62(4):286-91.

Edwards 2001 {unpublished data only}

Edwards P, Roberts I. A comparison of two questionnaires for assessing outcome after head injury. unpublished.

Edwards 2009 {published data only}

Edwards SL, Slattery ML, Edwards AM, Sweeney C, Murtaugh MA, Palmer LE, et al. Factors associated with response to a follow-up postal questionnaire in a cohort of American Indians. Preventive medicine 2009;48(6):596-9.

Edwards 2016a {published data only}

Edwards L, Salisbury C, Horspool K, Foster A, Garner K, Montgomery AA. Increasing follow-up questionnaire response rates in a randomized controlled trial of telehealth for depression: three embedded controlled studies. TRIALS 2016;17(1):107.

Edwards 2016b {published data only}

Edwards L, Salisbury C, Horspool K, Foster A, Garner K, Montgomery AA. Increasing follow-up questionnaire response rates in a randomized controlled trial of telehealth for depression: three embedded controlled studies. TRIALS 2016;17(1):107.

Edwards 2016c {published data only}

Edwards L, Salisbury C, Horspool K, Foster A, Garner K, Montgomery AA. Increasing follow-up questionnaire response rates in a randomized controlled trial of telehealth for depression: three embedded controlled studies. TRIALS 2016;17(1):107.

Elkind 1986 {published data only}

Elkind M, Tryon GS, De Vito AJ. Effects of type of postage and covering envelope on response rates in a mail survey. Psychological Reports 1986;59:279-83.

Enger 1993 {unpublished data only}

Enger JM. Survey questionnaire format effect on response rate and cost per return. Paper presented at the Annual Meeting of the American Educational Research Association, Atlanta 1993.

Erdogan 2002 {published data only}

Erdogan BZ, Baker MJ. Increasing mail survey response rates from an industrial population: a cost-effectiveness analysis of four follow-up techniques. Industrial Marketing Management 2002;31:65-73.

Ernst 2018 {published data only}

Ernst S A, Brand T, Lhachimi S K, Zeeb H. Combining Internet-Based and Postal Survey Methods in a Survey among Gynecologists: Results of a Randomized Trial. HEALTH SERVICES RESEARCH 2018;53(2):879-95.

Etter 1996 {published data only}

Etter J-F, Perneger TV, Rougemont A. Does sponsorship matter in patient satisfaction surveys? A randomized trial. Medical Care 1996;34(4):327-35.

Etter 1998a {published data only}

Etter J-F, Perneger TV, Ronchi A. Collecting saliva samples by mail. American Journal of Epidemiology 1998;147(2):141-6.

Etter 1998b {published data only}

Etter J-F, Perneger TV, Laporte J-D. Unexpected effects of a prior feedback letter and a professional layout on the response rate to a mail survey in Geneva. Journal of Epidemiology and Community Health 1998;52:128-9.

Etter 2002 {published data only}

Etter JF, Cucherat M, Perneger TV. Questionnaire color and response patterns in mailed surveys: a randomised trial and meta-analysis. Evaluation and the Health Professions 2002;25(2):185-99.

Etzel 1974 {published data only}

Etzel MJ, Walker BJ. Effects of alternative follow-up procedures on mail survey response rates. Journal of Applied Psychology 1974;59(2):219-21.

Evans 2004 {published data only}

Evans BR, Peterson BL, Demark-Wahnefried W. No difference in response rate to a mailed survey among prostate cancer survivors using conditional versus unconditional incentives. Cancer Epidemiology, Biomarkers & Prevention 2004;13(2):277-8.

Falthzik 1971 {published data only}

Falthzik AM, Carroll SJ. Rate of return for closed versus open-ended questions in a mail questionnaire survey of industrial organizations. Psychological Reports 1971;29:1121-2.

Faria 1990 {published data only}

Faria AJ, Dickinson JR, Filipic TV. The effect of telephone versus letter prenotification on mail survey response rate, speed, quality and cost. Journal of the Market Research Society 1990;32(4):551-68.

Faria 1992 {published data only}

Faria AJ, Dickinson JR. Mail survey response, speed, and cost. Industrial Marketing Management 1992;21:51-60.

Faria 1997 {published data only}

Faria MC, Mateus CL, Coelho F, Martins R, Barros H. Postal questionnaires: a useful strategy for the follow up of stroke cases? [Uma Estrategia util para o seguimento de doentes com Acidente Vascular Cerebral?]. Acta Medica Portugesa 1997;10:61-5.

Farley 2014 {published data only}

Farley K, Hanbury A, Thompson C. Gathering opinion leader data for a tailored implementation intervention in secondary healthcare: a randomised trial. BMC MEDICAL RESEARCH METHODOLOGY 2014;14:38.

Farmer 2005 {published data only}

Farmer A J, Doll H A. In a randomized trial, outcomes were not affected by intensive follow-up over 1 year. JOURNAL OF CLINICAL EPIDEMIOLOGY 2005;58(10):991-6.

Feigelson 2017 {published data only}

Feigelson Heather Spencer, McMullen Carmit K, Madrid Sarah, Sterrett Andrew T, Powers J David, Blum-Barnett Erica, et al. Optimizing patient-reported outcome and risk factor reporting from cancer survivors: a randomized trial of four different survey methods among colorectal cancer survivors. Journal of cancer survivorship : research and practice 2017;11(3):393-400.

Feild 1975 {published data only}

Feild HS. Effects of sex of investigator on mail survey response rates and response bias. Journal of Applied Psychology 1975;60(6):772-3.

Felix 2011 {published data only}

Felix L M, Burchett H E, Edwards P J. Factorial trial found mixed evidence of effects of pre-notification and pleading on response to Web-based survey. JOURNAL OF CLINICAL EPIDEMIOLOGY 2011;64(5):531-6.

Ferrell 1984 {published data only}

Ferrell OC, Childers TL, Reukert RW. Effects of situational factors on mail survey response. Educators' Conference Proceedings 1984;1:364-7.

Finn 1983 {published data only}

Finn DW. Response speeds, functions, and predictability in mail surveys. Journal of the Academy of Marketing Science 1983;11(2):61-70.

Finsen 2006 {published data only}

Finsen V, Storeheier AH. Scratch lottery tickets are a poor incentive to respond to mailed questionnaires. BMC Medical Research Methodology 2006;6(19):1-5.

Fiset 1994 {published data only}

Fiset L, Milgrom P, Tarnai J. Dentists' response to financial incentives in a mail survey of malpractice liability experience. Journal of Public Health Dentistry 1994;54(2):68-72.

Fluss 2014 {published data only}

Fluss E, Bond C M, Jones G T, Macfarlane G J. The effect of an internet option and single-sided printing format to increase the response rate to a population-based study: a randomized controlled trial. BMC MEDICAL RESEARCH METHODOLOGY 2014;9(14):104.

Ford 1967a {published data only}

Ford NM. The advance letter in mail surveys. Journal of Marketing Research 1967;4:202-4.

Ford 1967b {published data only}

Ford NM. The advance letter in mail surveys. Journal of Marketing Research 1967;4:202-4.

Ford 1968 {published data only}

Ford NM. Questionnaire appearance and response rates in mail surveys. Journal of Advertising Research 1968;8(3):43-5.

Foushee 1990 {published data only}

Foushee KD, McLellan RW. The effect of the timing of follow-up on response rates to international surveys. International Journal of Hospitality Management 1990;9(1):21-5.

Fowler 2019 {published data only}

Fowler Floyd J Jr, Cosenza Carol, Cripps Lauren A, Edgman-Levitan Susan, Cleary Paul D. The effect of administration mode on CAHPS survey response rates and results: A comparison of mail and web-based approaches. Health services research 2019;54(3):714-21.

Frederiks 2020 {published data only}

Frederiks E R, Romanach L M, Berry A, Toscas P. Making energy surveys more impactful: Testing material and non-monetary response strategies. ENERGY RESEARCH & SOCIAL SCIENCE 2020;63:101409.

Fredrickson 2005 {published data only}

Fredrickson D D, Jones T L, Molgaard C A, Carman C G, Schukman J, Dismuke S E, et al. Optimal design features for surveying low-income populations. JOURNAL OF HEALTH CARE FOR THE POOR AND UNDERSERVED 2005;16(4):677-90.

Freise 2001 {published data only}

Freise DC, Scheibler F, Pfaff H. Der zusammenhang zwischen fragebogenlange und der hohe des rucklaufs bei patientenbefragungen [Correlation between questionnaire length and response rate in patient surveys]. Gesundheitswesen 2001;63:A13.

Friedman 1975 {published data only}

Friedman HH, Goldstein L. Effect of ethnicity of signature on the rate of return and content of a mail questionnaire. Journal of Applied Psychology 1975;60(6):770-1.

Friedman 1979 {published data only}

Friedman HH, San Augustine AJ. The effects of a monetary incentive and the ethnicity of the sponsors signature on the rate and quality of response to a mail survey. Journal of the Academy of Marketing Science 1979;7(2):95-101.

Furse 1982 {published data only}

Furse DH, Stewart DW. Monetary incentives versus promised contribution to charity: new evidence on mail survey response. Journal of Marketing Research 1982;XIX:375-80.

Furst 1979 {published and unpublished data}

Furst LG, Blitchington WP. The use of a descriptive cover letter and secretary pre-letter to increase response rate in a mailed survey. Personnel Psychology 1979;32:155-9.

Futrell 1977 {published data only}

Futrell CM, Swan J. Anonymity and response by salespeople to a mail questionnaire. Journal of Marketing Research 1977;14:611-6.

Futrell 1978 {published data only}

Futrell CM, Stem DE, Fortune BD. Effects of signed versus unsigned internally administered questionnaires for managers. Journal of Business Research 1978;6:91-8.

Futrell 1981 {published data only}

Futrell CM, Lamb C. Effect on mail survey return rates of including questionnaires with follow up letters. Perceptual and Motor Skills 1981;52:11-5.

Futrell 1982 {published data only}

Futrell CM, Hise RT. The effects of anonymity and a same-day deadline on the response rate to mail surveys. European Research 1982;10:171-5.

Gajic 2012 {published data only}

Gajic Aleksandra, Cameron David, Hurley Jeremiah. The cost-effectiveness of cash versus lottery incentives for a web-based, stated-preference community survey. The European Journal of Health Economics 2012;13(6):789-99.

Gajraj 1990 {published data only}

Gajraj AM, Faria AJ, Dickinson JR. A comparison of the effect of promised and provided lotteries, monetary and gift incentives on mail survey response rate, speed and cost. Journal of the Market Research Society 1990;32(1):141-62.

Galesic 2009 {published data only}

Galesic Mirta, Bosnjak Michael. Effects of Questionnaire Length on Participation and Indicators of Response Quality in a Web Survey. PUBLIC OPINION QUARTERLY 2009;73(2):349-60.

Garcia 2014 {published data only}

Garcia Ivett, Portugal Cecilia, Chu Li-Hao, Kawatkar Aniket A. Response rates of three modes of survey administration and survey preferences of rheumatoid arthritis patients. Arthritis care & research 2014;66(3):364-70.

Gaski 2004a {published data only}

Gaski JF. Efficacy of a particular mail survey appeal: does it help to disclose that the purpose is a dissertation? Perceptual & Motor Skills 2004a;99(3 Pt 2):1295-8.

Gaski 2004b {published data only}

Gaski JF. Efficacy of a particular mail survey appeal: does it help to disclose that the purpose is a dissertation? Perceptual & Motor Skills 2004b;99(3 Pt 2):1295-8.

Gates 2009 {published data only}

Gates Simon, Williams Mark A, Withers Emma, Williamson Esther, Mt-Isa Shahrul, Lamb Sarah E. Does a monetary incentive improve the response to a postal questionnaire in a randomised controlled trial? The MINT incentive study. Trials 2009;10(101263253):44.

Gattellari 2001 {published data only}

Gattellari M, Ward JE. Will donations to their learned college increase surgeons' participation in surveys? A randomized trial. Journal of Clinical Epidemiology 2001;54:645-50.

Gattellari 2004 {published data only}

Gattellari M, Ward JE. Does a deadline improve men’s participation in self-administered health surveys? A randomized controlled trial in general practice. Journal of Public Health 2004;26(4):384-7.

Gattellari 2012 {published data only}

Gattellari M, Zwar N, Worthington J M. No difference demonstrated between faxed or mailed prenotification in promoting questionnaire response among family physicians: a randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2012;65(5):544-52.

Gendall 1996 {published data only}

Gendall P. The effect of questionnaire cover design in mail surveys. Marketing Bulletin 1996;7:30-8.

Gendall 1998 {published data only}

Gendall P, Hoek J, Brennan M. The tea bag experiment: more evidence on incentives in mail surveys. Journal of the Market Research Society 1998;40(4):347-51.

Gendall 2005a {published data only}

Gendall P. The effect of covering letter personalisation in mail surveys. International Journal of Market Research 2005a;47(4):376-82.

Gendall 2005b {published data only}

Gendall P. Can you judge a questionnaire by its cover? The effect of questionnaire cover design on mail survey response. International Journal of Public Opinion Research 2005b;17(3):346-61.

Gendall 2005c {published data only}

Gendall P, Leong M, Healey B. The effect of prepaid non-monetary incentives in mail surveys. ANZMAC 2005 Conference: Marketing Research and Research Methodologies (quantitative) 2005;1:21-7.

Gendall 2008 {published data only}

Gendall P, Healey B. Alternatives to Prepaid Monetary Incentives in Mail Surveys. International Journal of Public Opinion Research 2008;20(4):517–527.

Gibson 1999a {published data only}

Gibson PJ, Koepsell TD, Diehr P, Hale C. Increasing response rates for mailed surveys of medicaid clients and other low-income populations. American Journal of Epidemiology 1999;149(11):1057-62.

Gibson 1999b {published data only}

Gibson PJ, Koepsell TD, Diehr P, Hale C. Increasing response rates for mailed surveys of medicaid clients and other low-income populations. American Journal of Epidemiology 1999;149(11):1057-62.

Gibson 1999c {published data only}

Gibson PJ, Koepsell TD, Diehr P, Hale C. Increasing response rates for mailed surveys of medicaid clients and other low-income populations. American Journal of Epidemiology 1999;149(11):1057-62.

Giles 1978 {published data only}

Giles WF, Feild HS. Effects of amount, format, and location of demographic information on questionnaire return rate and response bias of sensitive and non sensitive items. Personnel Psychology 1978;31:549-59.

Gillpatrick 1994 {published and unpublished data}

Gillpatrick TR, Harmon RR, Tseng LP. The effect of a nominal monetary gift and different contacting approaches on mail survey response among engineers. IEE Transactions of Engineering Management 1994;41:285-90.

Gitelson 1992 {published data only}

Gitelson RJ, Drogin EB. An experiment on the efficacy of a certified final mailing. Journal of Leisure Research 1992;24(1):72-8.

Gjostein 2016 {published data only}

Gjostein D K, Huitfeldt A, Loberg M, Adami H O, Garborg K, Kalager M, et al. Incentives and participation in a medical survey. TIDSSKRIFT FOR DEN NORSKE LAEGEFORENING 2016;136(12-13):1082-7.

Glidewell 2012a {published data only}

Glidewell, L, Thomas, R, MacLennan, G, et al. Do incentives, reminders or reduced burden improve healthcare professional response rates in postal questionnaires? two randomised controlled trials. BMC HEALTH SERVICES RESEARCH 2012;14(12):250.

Glidewell 2012b {published data only}

Glidewell, L, Thomas, R, MacLennan, G, et al. Do incentives, reminders or reduced burden improve healthcare professional response rates in postal questionnaires? two randomised controlled trials. BMC HEALTH SERVICES RESEARCH 2012;14(12):250.

Glisan 1982 {published data only}

Glisan G, Grimm JL. Improving response rate in an industrial setting: will traditional variables work? Southern Marketing Association Proc 1982;20:265-8.

Godwin 1979 {published data only}

Godwin K. The consequences of large monetary incentives in mail surveys of elites. Public Opinion Quarterly 1979;43:378-87.

Goldstein 1975 {published data only}

Goldstein L, Friedman HH. A case for double postcards in surveys. J Advertising Research 1975;15:43-7.

Goodstadt 1977 {published data only}

Goodstadt MS, Chung L, Kronitz R, Cook G. Mail survey response rates: their manipulation and impact. Journal of Marketing Research 1977;14:391-5.

Goodwin 2020 {published data only}

Goodwin M, Walsh T, Whittaker W, Emsley R, Sutton M, Tickle M, et al. Increasing questionnaire response: evidence from a nested RCT within a longitudinal birth cohort study. BMC MEDICAL RESEARCH METHODOLOGY 2020;20(1):163.

Göritz 2004a {published data only}

Göritz AS. The impact of material incentives on response quantity, response quality,sample composition, survey outcome,and cost in online access panels. International Journal of Market Research 2004a;46(3):327-45.

Göritz 2004b {published data only}

Göritz AS. The impact of material incentives on response quantity, response quality,sample composition, survey outcome, and cost in online access panels. International Journal of Market Research 2004b;46(3):327-45.

Goulao 2020a {published data only}

Goulao B, Duncan A, Floate R, Clarkson J, Ramsay C. Three behavior change theory-informed randomized studies within a trial to improve response rates to trial postal questionnaires. JOURNAL OF CLINICAL EPIDEMIOLOGY 2020;122:35-41.

Goulao 2020b {published data only}

Goulao B, Duncan A, Floate R, Clarkson J, Ramsay C. Three behavior change theory-informed randomized studies within a trial to improve response rates to trial postal questionnaires. JOURNAL OF CLINICAL EPIDEMIOLOGY 2020;122:35-41.

Goulao 2020c {published data only}

Goulao B, Duncan A, Floate R, Clarkson J, Ramsay C. Three behavior change theory-informed randomized studies within a trial to improve response rates to trial postal questionnaires. JOURNAL OF CLINICAL EPIDEMIOLOGY 2020;122:35-41.

Green 1986 {published data only}

Green KE, Stager SF. The effects of personalization, sex, locale, and level taught on educators' responses to a mail survey. Journal of Experimental Education 1986;54:203-6.

Green 1989 {published data only}

Green KE, Kvidahl RF. Personalization and offers of results: effects on response rates. Journal of Experimental Education 1989;57:263-70.

Green 2000 {published data only}

Green RG, Murphy KD, Snyder SM. Should demographics be placed at the end or at the beginning of mailed questionnaires? An empirical answer to a persistent methodological question. Social Work Research 2000;24(4):237-40.

Greer 1994 {published data only}

Greer TV, Lohtia R. Effects of source and paper color on response rates in mail surveys. Industrial Marketing Management 1994;23:47-54.

Griffin 2011 {published data only}

Griffin, J M, Simon, A B, Hulbert, E, et al. A comparison of small monetary incentives to convert survey non-respondents: a randomized control trial. BMC MEDICAL RESEARCH METHODOLOGY 2011;11:81.

Griffith 1999 {published data only}

Griffith LE, Cook DJ, Guyatt GH, Charles CA. Comparison of open and closed questionnaire formats in obtaining demographic information from Canadian general internists. Journal of Clinical Epidemiology 1999;52(10):997-1005.

Groeneman 1986 {published data only}

Groeneman S. People respond to surveys when the price is right. Marketing News 1986;19:29.

Groves 2000 {published data only}

Groves BW, Olsson RH. Response rates to surveys with self-addressed, stamped envelopes versus a self-addressed label. Psychological Reports 2000;86:1226-8.

Gueguen 2003a {published data only}

Gueguen N, Legoherel P, Jacob C. Sollicitation de participation à une enquête par courriel:effet de la présence sociale et de l’attrait physique dudemandeur sur le taux de réponse. Revue canadienne des sciences du comportement 2003a;35(2):84-96.

Gueguen 2003b {published data only}

Gueguen N, Legoherel P, Jacob C. Sollicitation de participation à une enquête par courriel:effet de la présence sociale et de l’attrait physique dudemandeur sur le taux de réponse. Revue canadienne des sciences du comportement, 2003b;35(2):84-96.

Gullahorn 1959 {published data only}

Gullahorn JT, Gullahorn JE. Increasing returns from non-respondents. Public Opinion Quarterly 1959;23(1):119-21.

Gullahorn 1963 {published data only}

Gullahorn JE, Gullahorn JT. An investigation of the effects of three factors on response to mail questionnaires. Public Opinion Quarterly 1963;27:294-6.

Guo 2016 {published data only}

Guo Y M, Kopec J A, Cibere J, Li L C, Goldsmith C H. Population Survey Features and Response Rates: A Randomized Experiment. AMERICAN JOURNAL OF PUBLIC HEALTH 2016;106(8):1422-6.

Gupta 1997 {published data only}

Gupta L, Ward J, D'Este C. Differential effectiveness of telephone prompts by medical and nonmedical staff in increasing survey response rates: a randomised trial. Australian and New Zealand Journal of Public Health 1997;21(1):98-9.

Hackler 1973 {published data only}

Hackler JC, Bourgette P. Dollars, dissonance and survey returns. Public Opinion Quarterly 1973;37:276-81.

Hall 2013 {published data only}

Hall A E, Sanson-Fisher R W, Lynagh M C, Threlfall T, D'Este C A. Format and readability of an enhanced invitation letter did not affect participation rates in a cancer registry-based study: a randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2013;66(1):85-94.

Hall 2019 {published data only}

Hall Eric, Sanchez Travis, Stephenson Rob, Stein Aryeh D, Sineath Robert Craig, Zlotorzynska Maria, et al. Randomised controlled trial of incentives to improve online survey completion among internet-using men who have sex with men. Journal of epidemiology and community health 2019;73(2):156-61.

Halpern 2002 {published data only}

Halpern SD, Ubel PA, Berlin JA, Asch DA. Randomized trial of $5 versus $10 monetary incentives, envelope size, and candy to increase physician response rates to mailed questionnaires. Medical Care 2002;40(9):834-9.

Halpern 2011a {published data only}

Halpern Scott D, Kohn Rachel, Dornbrand-Lo Aaron, Metkus Thomas, Asch David A, Volpp Kevin G. Lottery-based versus fixed incentives to increase clinicians' response to surveys. Health services research 2011;46(5):1663-74.

Halpern 2011b {published data only}

Halpern Scott D, Kohn Rachel, Dornbrand-Lo Aaron, Metkus Thomas, Asch David A, Volpp Kevin G. Lottery-based versus fixed incentives to increase clinicians' response to surveys. Health services research 2011;46(5):1663-74.

Halpern 2011c {published data only}

Halpern Scott D, Kohn Rachel, Dornbrand-Lo Aaron, Metkus Thomas, Asch David A, Volpp Kevin G. Lottery-based versus fixed incentives to increase clinicians' response to surveys. Health services research 2011;46(5):1663-74.

Hammink 2010 {published data only}

Hammink A, Giesen P, Wensing M. Pre-notification did not increase response rate in addition to follow-up: a randomized trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2010;63(11):1276-8.

Han 2013 {published data only}

Han Daifeng, Montaquila Jill M, Brick J Michael. An evaluation of incentive experiments in a two-phase address-based sample mail survey. Survey Research Methods 2013;7(3):207-18.

Hancock 1940 {published data only}

Hancock JW. An experimental study of four methods of measuring unit costs of obtaining attitude toward the retail store. Journal of Applied Psychology 1940;24:213-30.

Hansen 1980a {published data only}

Hansen RA, Robinson LM. Testing the effectiveness of alternative foot-in-the-door manipulations. Journal of Marketing Research 1980;17:359-64.

Hansen 1980b {published data only}

Hansen RA. A self-perception interpretation of the effect of monetary and nonmonetary incentives on mail survey respondent behaviour. Journal of Marketing Research 1980;17:77-83.

Hardigan 2012 {published data only}

Hardigan Patrick C, Succar Claudia Tammy, Fleisher Jay M. An analysis of response rate and economic costs between mail and web-based surveys among practicing dentists: a randomized trial. Journal of community health 2012;37(2):383-94.

Hardigan 2016 {published data only}

Hardigan Patrick C, Popovici Ioana, Carvajal Manuel J. Response rate, response time, and economic costs of survey research: A randomized trial of practicing pharmacists. Research in social & administrative pharmacy : RSAP 2016;12(1):141-8.

Hardy 2016 {published data only}

Hardy P, Bell J L, Brocklehurst P. Evaluation of the effects of an offer of a monetary incentive on the rate of questionnaire return during follow-up of a clinical trial: a randomised study within a trial. BMC MEDICAL RESEARCH METHODOLOGY 2016;16:82.

Harris 1978 {published data only}

Harris JR, Guffey Jr HJ. Questionnaire returns: stamps versus business reply envelopes revisited. Journal of Marketing Research 1978;15:290-3.

Harris 2008 {published data only}

Harris IA, Khoo OK, Young JM, Solomon MJ, Rae H. Lottery incentives did not improve response rate to a mailed survey: a randomized controlled trial. Journal of Clinical Epidemiology 2008;61(6):609-10.

Harrison 2002 {published data only}

Harrison RA, Holt D, Elton PJ. Do postage-stamps increase response rates to postal surveys? A randomized controlled trial. International Journal of Epidemiology 2002;31:872-4.

Harrison 2004 {published data only}

Harrison RA, Cock D. Increasing response to a postal survey of sedentary patients – a randomised controlled trial. BMC Health Services Research 2004;4(31):1-5.

Harvey 1986 {published data only}

Harvey L. A research note on the impact of class-of-mail on response rates to mailed questionnaires. Journal of the Market Research Society 1986;28(3):299-300.

Hatch 2017 {published data only}

Hatch R, Young D, Barber V, Harrison D A, Watkinson P. The effect of postal questionnaire burden on response rate and answer patterns following admission to intensive care: a randomised controlled trial. BMC MEDICAL RESEARCH METHODOLOGY 2017;17(1):49.

Hathaway 2021a {published data only}

Hathaway C A, Chavez M N, Kadono M, Ketcher D, Rollison D E, Siegel E M, et al. Improving Electronic Survey Response Rates Among Cancer Center Patients During the COVID-19 Pandemic: Mixed Methods Pilot Study. JMIR CANCER 2021;7(3):e30265.

Hathaway 2021b {published data only}

Hathaway C A, Chavez M N, Kadono M, Ketcher D, Rollison D E, Siegel E M, et al. Improving Electronic Survey Response Rates Among Cancer Center Patients During the COVID-19 Pandemic: Mixed Methods Pilot Study. JMIR CANCER 2021;7(3):e30265.

Hathaway 2021c {published data only}

Hathaway C A, Chavez M N, Kadono M, Ketcher D, Rollison D E, Siegel E M, et al. Improving Electronic Survey Response Rates Among Cancer Center Patients During the COVID-19 Pandemic: Mixed Methods Pilot Study. JMIR CANCER 2021;7(3):e30265.

Hathaway 2021d {published data only}

Hathaway C A, Chavez M N, Kadono M, Ketcher D, Rollison D E, Siegel E M, et al. Improving Electronic Survey Response Rates Among Cancer Center Patients During the COVID-19 Pandemic: Mixed Methods Pilot Study. JMIR CANCER 2021;7(3):e30265.

Hauw‐Berlemont 2020 {published data only}

Hauw-Berlemont Caroline, Serra Alexis, Groves Holden, Dzierba Amy, Louh Irene, Patel Mona, et al. The Source of the Message Matters: A Randomized Study Evaluating the Impact of a Survey Source on Response Rate. Annals of the American Thoracic Society 2020;17(4):525-7.

Hawkins 1979 {published data only}

Hawkins DI. The impact of sponsor identification and direct disclosure of respondent rights on the quantity and quality of mail survey data. Journal of Business 1979;52(4):577-90.

Hawley 2009 {published data only}

Hawley Kristin M, Cook Jonathan R, Jensen-Doss Amanda. Do noncontingent incentives increase survey response rates among mental health providers? A randomized trial comparison. Administration and policy in mental health 2009;36(5):343-8.

Heaton 1965 {published data only}

Heaton E. Increasing mail questionnaire returns with a preliminary letter. Journal of Advertising Research 1965;5:36-9.

Heerwegh 2005a {published data only}

Heerwegh D, Vanhove T, Matthijs K, Loosveldt G. The effect of personalizing on response rates and data quality in web surveys. International Journal of Social Research Methodology 2005a;8(2):85-99.

Heerwegh 2005b {published data only}

Heerwegh D. Effects of personal salutations in e-mail invitations to participate in a web survey. Public Opinion Quarterly 2005b;69(4):588-98.

Heerwegh 2006 {published data only}

Heerwegh D, Loosveldt G. Personalizing e-mail contacts: its influence on web survey response rate and social desirability response bias. International Journal of Public Opinion Research 2006;19(2):258-68.

Hendrick 1972 {published data only}

Hendrick C, Borden R, Giesen M, Murray EJ, Seyfried BA. Effectiveness of ingratiation tactics in a cover letter on mail questionnaire response. Psychonomic Science 1972;26(6):349-51.

Hendriks 2001 {published data only}

Hendriks AAJ, Vrielink MR, Smets EMA, Es SQ, Haes JCJM. Improving the assessment of (in)patients' satisfaction with hospital care. Medical Care 2001;39(3):270-83.

Henley 1976 {published data only}

Henley JR. Response rate to mail questionnaires with a return deadline. Public Opinion Quarterly 1976;40:374-5.

Hensley 1974 {published data only}

Hensley WE. Increasing response rate by choice of postage stamp. Current Opinion Quarterly 1974;38:280-3.

Hewett 1974 {published data only}

Hewett WC. How different combinations of postage on outgoing and return envelopes affect questionnaire returns. Journal of the Market Research Society 1974;16(1):49-50.

Hickey 2021 {published data only}

Hickey Michael, McIntyre Lauralyn, Taljaard Monica, Abdulaziz Kasim, Yadav Krishan, Hickey Carly, et al. Effect of prenotification on the response rate of a postal survey of emergency physicians: a randomised, controlled, assessor-blind trial. BMJ open 2021;11(9):e052843.

Hoffman 1998 {published data only}

Hoffman SC, Burke AE, Helzlsouer KJ, Comstock GW. Controlled trial of the effect of length, incentives, and follow-up techniques on response to a mailed questionnaire. American Journal of Epidemiology 1998;148(10):1007-11.

Hohwu 2013 {published data only}

Hohwu L, Lyshol H, Gissler M, Jonsson S H, Petzold M, Obel C. Web-Based Versus Traditional Paper Questionnaires: A Mixed-Mode Survey With a Nordic Perspective. JOURNAL OF MEDICAL INTERNET RESEARCH 2013;15(8):e173.

Hopkins 1988 {published data only}

Hopkins KD, Hopkins BR, Schon I. Mail surveys of professional populations: the effects of monetary gratuities on return rates. Journal of Experimental Education 1988;56:173-5.

Horn 2010 {published data only}

Horn Rachel, Jones Steve, Warren Kate. The cost-effectiveness of postal and telephone methodologies in increasing routine outcome measurement response rates in CAMHS. Child and Adolescent Mental Health 2010;15(1):60-3.

Hornik 1981 {published data only}

Hornik J. Time cue and time perception effect on response to mail surveys. Journal of Marketing Research 1981;18:243-8.

Hornik 1982 {published data only}

Hornik J. Impact of pre-call request form and gender interaction on response to a mail survey. Journal of Marketing Research 1982;19:144-51.

Horowitz 1974 {published data only}

Horowitz JL, Sedlacek WE. Initial returns on mail questionnaires: a literature review and research note. Research in Higher Education 1974;2:361-7.

Houston 1975 {published data only}

Houston MJ, Jefferson RW. The negative effects of personalization on response patterns in mail surveys. Journal of Marketing Research 1975;12:114-7.

Houston 1977 {published data only}

Houston MJ, Nevin JR. The effect of source and appeal on mail survey response patterns. Journal of Marketing Research 1977;14:374-8.

Hubbard 1988a {published data only}

Hubbard R, Little EL. Promised contributions to charity and mail survey responses: replication with extension. Public Opinion Quarterly 1988;52:223-30.

Hubbard 1988b {published data only}

Hubbard R, Little EL. Cash prizes and mail survey response rates: a threshold analysis. Journal of the Academy of Marketing Science 1988;16(3&4):42-4.

Huck 1974 {published data only}

Huck SW, Gleason E. Using monetary inducements to increase response rates from mailed surveys. Journal of Applied Psychology 1974;59(2):222-5.

Hyett 1977 {published data only}

Hyett GP, Farr DJ. Postal questionnaires: double-sided printing compared with single-sided printing. European Research 1977;5:136-7.

Iglesias 2000 {published data only}

Iglesias CP, Torgerson DJ. Does length of questionnaire matter? A randomised trial of response rates to a mailed questionnaire. Journal of Health Services Research and Policy 2000;5(2):19-21.

Iglesias 2001 {published data only}

Iglesias CP, Birks YF, Torgerson DJ. Improving the measurement of quality of life in older people: the York SF-12. Quarterly Journal of Medicine 2001;94:695-8.

Iversen 2020 {published data only}

Iversen Hilde Hestad, Holmboe Olaf, Bjertnaes Oyvind. Patient-reported experiences with general practitioners: a randomised study of mail and web-based approaches following a national survey. BMJ open 2020;10(10):e036533.

Jacob 2012 {published data only}

Jacob Robin Tepper, Jacob Brian. Prenotification, Incentives, and Survey Modality: An Experimental Test of Methods to Increase Survey Response Rates of School Principals. Journal of Research on Educational Effectiveness 2012;5(4):401-18.

Jacobs 1986 {published data only}

Jacobs LC. Effect of the use of optical scan sheets on survey response rate. Paper presented at the annual meeting of the American Educational Research Association 1986.

Jacoby 1990 {published data only}

Jacoby A. Possible factors affecting response to postal questionnaires: findings from a study of general practitioner services. Journal of Public Health Medicine 1990;12(2):131-5.

James 1990a {published data only}

James J, Bolstein R. The effect of monetary incentives and follow-up mailings on the response rate and response quality in mail surveys. Public Opinion Quarterly 1990;54:346-61.

James 1990b {published data only}

James J, Bolstein R. The effect of monetary incentives and follow-up mailings on the response rate and response quality in mail surveys. Public Opinion Quarterly 1990;54:346-61.

James 1992 {published data only}

James J, Bolstein R. Large monetary incentives and their effect on mail survey response rates. Public Opinion Quarterly 1992;56:442-53.

James 2011 {published data only}

James Katherine M, Ziegenfuss Jeanette Y, Tilburt Jon C, Harris Ann M, Beebe Timothy J. Getting physicians to respond: the impact of incentive type and timing on physician survey response rates. Health services research 2011;46(1 Pt 1):232-42.

James 2019 {published data only}

James S, Parker A, Torgerson D. Pen and Social Incentive Letter Retention Study within a Trial (SWAT) - An embedded, factorial design randomised controlled trial to investigate whether the inclusion of a pen and/or social incentive text cover letter included with the 12-month postal que. TRIALS 2019;20(Suppl 1):P-183.

Jamtvedt 2008 {published data only}

Jamtvedt G, Rosenbaum S, Dahm KT, Flottorp S. Chocolate bar as an incentive did not increase response rate among physiotherapists: a randomised controlled trial. BMC Research Notes 2008;1(34):1-4.

Jenkinson 2003 {published data only}

Jenkinson C, Coulter A, Reeves R, Bruster S, Richards N. Properties of the Picker Patient Experience questionnaire in a randomized controlled trial of long versus short form survey instruments. Journal of Public Health Medicine 2003;25(3):197–201.

Jensen 1994 {published data only}

Jensen JL. The effect of survey format on response rate and patterns of response. Doctoral Dissertation 1994.

Jepson 2005a {published data only}

Jepson C, Asch DA, Hershey JC, Ubel PA. In a mailed physician survey, questionnaire length had a threshold effect on response rate. Journal of Clinical Epidemiology 2005a;58(1):103-5.

Jepson 2005b {published data only}

Jepson C, Asch DA, Hershey JC, Ubel PA. In a mailed physician survey, questionnaire length had a threshold effect on response rate. Journal of Clinical Epidemiology 2005b;58(1):103-5.

Jobber 1983 {published data only}

Jobber D, Sanderson S. The effects of a prior letter and coloured questionnaire paper on mail survey response rates. Journal of the Market Research Society 1983;25(4):339-49.

Jobber 1985 {published data only}

Jobber D, Sanderson S. The effect of two variables on industrial mail survey returns. Industrial Marketing Management 1985;14:119-21.

Jobber 1988 {published data only}

Jobber D, Birro K, Sanderson SM. A factorial investigation of methods of stimulating response to mail surveys. European Journal of Operational Research 1988;37:158-64.

Jobber 1989 {published data only}

Jobber D. An examination of the effects of questionnaire factors on response to an industrial mail survey. International Journal of Research in Marketing 1989;6:129-40.

Jobber D 1985 {published data only}

Jobber D, Allen N, Oakland J. The impact of telephone notification strategies on response to an industrial mail survey. International Journal of Research Marketing 1985;2:291-8.

Johansson 1997a {published data only}

Johansson L, Solvoll K, Opdahl S, Bjorneboe G-E, Drevon CA. Response rates with different distribution methods and reward, and reproducibility of a quantitative food frequency questionnaire. European Journal of Clinical Nutrition 1997;51:346-53.

Johansson 1997b {published data only}

Johansson L, Solvoll K, Opdahl S, Bjorneboe G-E, Drevon CA. Response rates with different distribution methods and reward, and reproducibility of a quantitative food frequency questionnaire. European Journal of Clinical Nutrition 1997;51:346-53.

Johansson 1997c {published data only}

Johansson L, Solvoll K, Opdahl S, Bjorneboe G-E, Drevon CA. Response rates with different distribution methods and reward, and reproducibility of a quantitative food frequency questionnaire. European Journal of Clinical Nutrition 1997;51:346-53.

John 1994 {published data only}

John EM, Savitz DA. Effect of a monetary incentive on response to a mail survey. Annals of Epidemiology 1994;4(3):231-5.

Joinson 2005a {published data only}

Joinson AN, Reips UD. Personalized salutation, power of sender and response rates to Web-based surveys. Computers in Human Behavior 2005a;23(3):1-12.

Joinson 2005b {published data only}

Joinson AN, Reips UD. Personalized salutation, power of sender and response rates to Web-based surveys. Computers in Human Behavior 2005b;23(3):1-10.

Joinson 2005c {published data only}

Joinson AN, Reips UD. Personalized salutation, power of sender and response rates to Web-based surveys. Computers in Human Behavior 2005;23(3):1-10.

Joinson 2007a {published data only}

Joinson AN, Woodley A, Reips UD. Personalization, authentication and self-disclosure in self-administered Internet surveys. Computers in Human Behavior 2007a;23:275–85.

Joinson 2007b {published data only}

Joinson AN, Woodley A, Reips UD. Personalization, authentication and self-disclosure in self-administered Internet surveys. Computers in Human Behavior 2007b;23:275–85.

Jones 1978 {published data only}

Jones WH, Linda G. Multiple criteria effects in a mail survey experiment. Journal of Marketing Research 1978;15:280-4.

Jones 2000 {published data only}

Jones R, Zhou M, Yates WR. Improving return rates for health-care outcome. Psychological Reports 2000;87:639-42.

Junghans 2005 {published data only}

Junghans C, Feder G, Hemingway H, Timmis A, Jones M. Recruiting patients to medical research: double blind randomised trial of "opt-in" versus "opt-out" strategies. BMJ 2005;331(940-):1-4.

Juszczak 2021 {published data only}

Juszczak E, Hewer O, Partlett C, Hurd M, Bari V, Bowler U, et al. Evaluation of the effectiveness of an incentive strategy on the questionnaire response rate in parents of premature babies: a randomised controlled Study Within A Trial (SWAT) nested within SIFT. TRIALS 2021;22(1):554.

Kahle 1978 {published data only}

Kahle LR, Sales BD. Personalization of the outside envelope in mail surveys. Public Opinion Quarterly 1978;42:547-50.

Kalafatis 1995 {published data only}

Kalafatis SP, Madden FJ. The effect of discount coupons and gifts on mail survey response rates among high involvement respondents. Journal of the Market Research Society 1995;37(2):171-84.

Kalantar 1999 {published data only}

Kalantar JS, Talley NJ. The effects of lottery incentive and length of questionnaire on health survey response rates: a randomized study. Journal of Clinical Epidemiology 1999;52(11):1117–22.

Kaplan 1970a {published data only}

Kaplan S, Cole P. Factors affecting response to postal questionnaires. British Journal of Preventive and Social Medicine 1970a;24:245-7.

Kaplan 1970b {published data only}

Kaplan S, Cole P. Factors affecting response to postal questionnaires. British Journal of Preventive and Social Medicine 1970b;24:245-7.

Kaplowitz 2004 {published data only}

Kaplowitz MD, Lupi F. Color photographs and mail survey response rates. International Journal of Public Opinion Research 2004;16(2):199-206.

Kasprzyk 2001 {published data only}

Kasprzyk D, Montano DE, St Lawrence JS, Phillips WR. The effects of variations in mode of delivery and monetary incentive on physicians' responses to a mailed survey assessing STD practice patterns. Evaluation and the Health Professions 2001;24(1):3-17.

Kawash 1971 {published data only}

Kawash MB, Aleamoni LM. Effect of a personal signature on the initial rate of return of a mailed questionnaire. Journal of Applied Psychology 1971;55(6):589-92.

Keating 2008 {published data only}

Keating Nancy L, Zaslavsky Alan M, Goldstein Judy, West Dee W, Ayanian John Z. Randomized trial of $20 versus $50 incentives to increase physician survey response rates. Medical care 2008;46(8):878-81.

Keding 2016a {published data only}

Keding Ada, Brabyn Sally, MacPherson Hugh, Richmond Stewart J, Torgerson David J. Text message reminders to improve questionnaire response rates. Journal of clinical epidemiology 2016;79(jce, 8801383):90-5.

Keding 2016b {published data only}

Keding Ada, Brabyn Sally, MacPherson Hugh, Richmond Stewart J, Torgerson David J. Text message reminders to improve questionnaire response rates. Journal of clinical epidemiology 2016;79(jce, 8801383):90-5.

Keding 2016c {published data only}

Keding Ada, Brabyn Sally, MacPherson Hugh, Richmond Stewart J, Torgerson David J. Text message reminders to improve questionnaire response rates. Journal of clinical epidemiology 2016;79(jce, 8801383):90-5.

Keeter 2001 {published data only}

Keeter S, Kennamer JD, Ellis JM, Green RG. Does the use of colored paper improve response rate to mail surveys?: A multivariate experimental evaluation. Journal of Social Service Research 2001;28(1):69-78.

Kenyon 2005 {published data only}

Kenyon S, Pike K, Jones D, Taylor D, Salt A, Marlow N, et al. The effect of a monetary incentive on return of a postal health and development questionnaire: a randomised trial. BMC Health Services Research 2005;5(55):1-4.

Keown 1985a {published data only}

Keown CF. Foreign mail surveys: response rates using monetary incentives. Journal of International Business Studies 1985;16:151-3.

Keown 1985b {published data only}

Keown CF. Foreign mail surveys: response rates using monetary incentives. Journal of International Business Studies 1985;16:151-3.

Kephart 1958 {published data only}

Kephart WM, Bressler M. Increasing the response to mail questionnaires: a research study. Public Opinion Quarterly 1958;21:123-32.

Kereakoglow 2013 {published data only}

Kereakoglow S, Gelman R, Partridge A H. Evaluating the effect of esthetically enhanced materials compared to standard materials on clinician response rates to a mailed survey. INTERNATIONAL JOURNAL OF SOCIAL RESEARCH METHODOLOGY 2013;16(4):301-6.

Kerin 1976 {published data only}

Kerin RA, Harvey MG. Methodological considerations in corporate mail surveys: a research note. Journal of Business Research 1976;4(3):277-81.

Kerin 1981 {published data only}

Kerin RA, Barry TE, Dubinsky AJ, Harvey MG. Offer of results and mail survey response from a commercial population: a test of Gouldner's Norm of Reciprocity. Proceeding of the American Institute of Decision Sciences 1981;1:283-5.

Kernan 1971 {published data only}

Kernan JB. Are 'bulk rate occupants' really unresponsive? Public Opinion Quarterly 1971;35:420-2.

Khadjesari 2011a {published data only}

Khadjesari Z, Murray E, Kalaitzaki E, White I R, McCambridge J, Thompson S G, et al. Impact and Costs of Incentives to Reduce Attrition in Online Trials: Two Randomized Controlled Trials. JOURNAL OF MEDICAL INTERNET RESEARCH 2011;13(1):e26.

Khadjesari 2011b {published data only}

Khadjesari Z, Murray E, Kalaitzaki E, White I R, McCambridge J, Thompson S G, et al. Impact and Costs of Incentives to Reduce Attrition in Online Trials: Two Randomized Controlled Trials. JOURNAL OF MEDICAL INTERNET RESEARCH 2011;13(1):e26.

Kilsdonk 2015 {published data only}

Kilsdonk E, Dulmen-den Broeder E, Pal H J, Hollema N, Kremer L C, den Heuvel-Eibrink M M, et al. Effect of Web-Based Versus Paper-Based Questionnaires and Follow-Up Strategies on Participation Rates of Dutch Childhood Cancer Survivors: A Randomized Controlled Trial. JMIR CANCER 2015;1(2):e11.

Kindra 1985 {published data only}

Kindra GS, McGown KL, Bougie M. Stimulating responses to mailed questionnaires. An experimental study. International Journal of Research in Marketing 1985;2:219-35.

King 1978 {published data only}

King JO. The influence of personalization on mail survey response rates. Arkansas Business and Economic Review 1978;11:15-8.

Koloski 2001 {published data only}

Koloski NA, Talley NJ, Boyce PM, Morris-Yates AD. The effects of questionnaire length and lottery ticket inducement on the response rate in mail surveys. Psychology and Health 2001;16:67-75.

Koloski 2013 {published data only}

Koloski N A, Jones M, Eslick G, Talley N J. Predictors of Response Rates to a Long Term Follow-Up Mail out Survey. PLOS ONE 2013;8(11):e79179.

Koo 1995 {published data only}

Koo MM, Rohan TE. Printed signatures and response rates. Epidemiology 1995;6(5):568.

Koo 1996 {published data only}

Koo MM, Rohan TE. Types of advance notification in reminder letters and response rates. Epidemiology 1996;7(2):215-6.

Kost 2018 {published data only}

Kost Rhonda G, Correa Da Rosa Joel. Impact of survey length and compensation on validity, reliability, and sample characteristics for Ultrashort-, Short-, and Long-Research Participant Perception Surveys. Journal of Clinical and Translational Science 2018;2(1):31-7.

Kropf 2005 {published data only}

Kropf ME, Blair J. Eliciting survey cooperation: incentives, self-interest, and norms of cooperation. Evaluation Review 2005;29(6):559-75.

Kurth 1987 {unpublished data only}

Kurth LA. Message responses as functions of communication mode: a comparison of electronic mail and typed memoranda. Doctoral dissertation 1987.

Kuskowska‐Wolk 1992 {published data only}

Kuskowska-Wolk A, Holte S, Ohlander EM, Bruce A, Holmberg L, Adami HO, et al. Effects of different designs and extension of a food frequency questionnaire on response rate, completeness of data and food frequency responses. International Journal of Epidemiology 1992;21(6):1144-50.

Kypri 2003 {published data only}

Kypri K, Gallagher SJ. Incentives to increase participation in an Internet survey of alcohol use: a controlled experiment. Alcohol & Alcoholism 2003;38(5):437-41.

Kypri 2016 {published data only}

Kypri K, Maclennan B, Connor J L. Effects of small incentives on survey response fractions: randomised comparisons in national alcohol surveys conducted in New Zealand. EUROPEAN JOURNAL OF PUBLIC HEALTH 2016;26(3):430-U12.

Labarere 2000 {published data only}

Labarere J, Francois P, Bertrand D, Fourny M, Olive F, Peyrin JC. Survey of inpatient satisfaction: comparison of different survey methods [Evaluation de la satisfaction des patients hospitalises: Comparaison de plusieurs methodes d'enquete]. La Presse Medicale 2000;29:1112-4.

Labrecque 1978 {published data only}

Labrecque DP. A response rate experiment using mail questionnaires. Journal of Marketing 1978;42:82-3.

La Garce 1995 {published data only}

La Garce R, Kuhn LD. The effect of visual stimuli on mail survey response rates. Industrial Marketing Management 1995;24:11-8.

Lagerros 2012 {published data only}

Lagerros Y T, Sandin S, Bexelius C, Litton J E, Lof M. Estimating physical activity using a cell phone questionnaire sent by means of short message service (SMS): a randomized population-based study. EUROPEAN JOURNAL OF EPIDEMIOLOGY 2012;27(7):561-6.

Langenderfer‐Magruder 2020 {published data only}

Langenderfer-Magruder Lisa, Wilke Dina J. The Use of Text Message Reminders to Increase Completion of Web-Based Surveys: Results of Two Randomized Control Trials. Journal of Technology in Human Services 2020;38(1):22-37.

Lavelle 2008 {published data only}

Lavelle K, Todd C, Campbell M. Do postage stamps versus pre-paid envelopes increase responses to patient mail surveys? A randomised controlled trial. BMC Health Services Research 2008;8(113):1-5.

Leece 2004 {published data only}

Leece P, Bhandari M, Sprague S, Swiontkowski M F, Schemitsch E H, Tornetta P, et al. Internet versus mailed questionnaires: A randomized comparison (2). JOURNAL OF MEDICAL INTERNET RESEARCH 2004;6(3):26-33.

Leece 2006a {published data only}

Leece P, Bhandari M, Sprague S, Swiontkowski MF, Schemitsch EH, Tornetta P. Does flattery work? A comparison of 2 different cover letters for an international survey of orthopedic surgeons. Canadian Journal of Surgery 2006a;49(2):90-5.

Leece 2006b {published data only}

Leece P, Bhandari M, Sprague S, Swiontkowski MF, Schemitsch EH, Tornetta P. Does flattery work? A comparison of 2 different cover letters for an international survey of orthopedic surgeons. Canadian Journal of Surgery 2006b;49(2):90-5.

Leigh Brown 1997 {published data only}

Leigh Brown AP, Lawrie HE, Kennedy AD, Webb JA, Torgerson DJ, Grant AM. Cost effectiveness of a prize draw on response to a postal questionnaire: results of a randomised trial among orthopaedic outpatients in Edinburgh. Journal of Epidemiology and Community Health 1997;51:463-4.

Leung 2002 {published data only}

Leung GM, Ho LM, Chan MF, Johnston JM, Wong FK. The effects of cash and lottery incentives on mailed surveys to physicians: a randomized trial. Journal of Clinical Epidemiology 2002;55:801-7.

Leung 2004 {published data only}

Leung GM, Johnston JM, Saing H, Tin KY, Wong IO, Ho, LM. Prepayment was superior to postpayment cash incentives in a randomized postal survey among physicians. Journal of Clinical Epidemiology 2004;57(8):777-84.

Levy 2012 {published data only}

Levy R M, Shapiro M, Halpern S D, Ming M E. Effect of Personalization and Candy Incentive on Response Rates for a Mailed Survey of Dermatologists. JOURNAL OF INVESTIGATIVE DERMATOLOGY 2012;132(3):724-6.

Lewis 2017 {published data only}

Lewis H, Keding A, Bosanquet K, Gilbody S, Torgerson D. An randomized controlled trial of Post-it® notes did not increase postal response rates in older depressed participants. Journal of Evaluation in Clinical Practice 2017;23(1):102-7.

Lewis 2017a {published data only}

Lewis T, Hess K. The Effect of Alternative E-mail Contact Timing Strategies on Response Rates in a Self-administered Web Survey. Field Methods 2017;29(4):351-64.

Linsky 1965 {published data only}

Linsky AS. A factorial experiment in inducing responses to a mail questionnaire. Sociology and Social Research 1965;49:183-9.

Little 1990 {published data only}

Little EL, Engelbrecht EG. The use of incentives to increase mail survey response rates in a business environment. Journal of Direct Marketing 1990;4(4):46-9.

Loban 2017 {published data only}

Loban A, Mandefield L, Hind D, Bradburn M. A randomized trial found online questionnaires supplemented by postal reminders generated a cost-effective and generalizable sample but don't forget the reminders. Journal of Clinical Epidemiology 2017;92:116-25.

London 1990a {published data only}

London SJ, Dommeyer CJ. Increasing response to industrial mail surveys. Industrial Marketing Management 1990;19:235-41.

London 1990b {published data only}

London SJ, Dommeyer CJ. Increasing response to industrial mail surveys. Industrial Marketing Management 1990;19:235-41.

Lorenzi 1988 {published data only}

Lorenzi P, Friedman R, Paolollo JGP. Consumer mail survey responses: more (unbiased) bang for the buck. Journal of Consumer Marketing 1988;5(4):31-40.

Lund 1998 {published data only}

Lund E, Gram IT. Response rate according to title and length of questionnaire. Scandinavian Journal of Social Medicine 1998;26(2):154-60.

Lusinchi 2007 {published data only}

Lusinchi D. Increasing response rates & data quality of Web surveys: Pre-notification and questionnaire paging format. https://nces.ed.gov/FCSM/pdf/2007FCSM_Lusinchi-X-A.pdf 2007.

MacLennan 2013 {published data only}

MacLennan Graeme, McDonald Alison, McPherson Gladys, Avenell Alison. Do advance telephone calls ahead of reminder questionnaires increase response rate in non-responders compared to questionnaire reminders only: The record phone trial. Clinical Trials 2013;10(SUPPL. 2):S1.

Maheux 1989a {published data only}

Maheux B, Legault C, Lambert J. Increasing response rates in physicians' mail surveys: an experimental study. American Journal of Public Health 1989;79(5):638-9.

Maheux 1989b {published data only}

Maheux B, Legault C, Lambert J. Increasing response rates in physicians' mail surveys: an experimental study. American Journal of Public Health 1979;79(5):638-9.

Mallen 2008 {unpublished data only}

Mallen C, Dunn KM, Thomas E, Peat G. Thicker paper and larger font increased response and completeness in a postal survey. Journal of Clinical Epidemiology 2008;61(12):1296-300.

Man 2011 {published data only}

Man M S, Tilbrook H E, Jayakody S, Hewitt C E, Cox H, Cross B, et al. Electronic reminders did not improve postal questionnaire response rates or response times: a randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2011;64(9):1001-4.

Mann 2005 {published data only}

Mann CB. Do advance letters improve preelection forecast accuracy? Public Opinion Quarterly 2005;69(4):561-71.

Mann 2008 {published data only}

Mann S L, Lynn D J, Peterson A V. The "Downstream" effect of token prepaid cash incentives to parents on their young adult children's survey participation. PUBLIC OPINION QUARTERLY 2008;72(3):487-501.

Marcus 2007 {published data only}

Marcus B, Bosnjak M, Lindner S, Pilischenko S, Schütz A. Compensating for low topic interest and long surveys. A field experiment on nonresponse in web surveys. Social Science Computer Review 2007;25:372-83.

Marrett 1992 {published data only}

Marrett LD, Kreiger N, Dodds L, Hilditch S. The effect on response rates of offering a small incentive with a mailed questionnaire. AEP 1992;2(5):745-53.

Marsh 1999 {published data only}

Marsh P, Kendrick D. Using a diary to record near misses and minor injuries - which method of administration is best? Injury Prevention 1999;5:305-9.

Martin 1970 {published data only}

Martin JD, McConnell JP. Mail questionnaire response induction: the effect of four variables on the response of a random sample to a difficult questionnaire. Social Science Quarterly 1970;51:409-14.

Martin 1989 {published data only}

Martin WS, Duncan WJ, Powers TL, Sawyer JC. Costs and benefits of selected response inducement techniques in mail survey research. Journal of Business Research 1989;19:67-79.

Martin 1994 {published data only}

Martin CL. The impact of topic interest on mail survey response behaviour. Journal of the Market Research Society 1994;36(4):327-38.

Martinson 2000 {published data only}

Martinson BC, Lazovich D, Lando HA, Perry CL, McGovern PG, Boyle RG. Effectiveness of monetary incentives for recruiting adolescents to an intervention trial to reduce smoking. Preventive Medicine 2000;31:706-13.

Mason 1961 {published data only}

Mason WS, Dressel RJ, Bain RK. An experimental study of factors affecting response to a mail survey of beginning teachers. Public Opinion Quarterly 1961;25:296-9.

Matteson 1974 {published data only}

Matteson MT. Type of transmittal letter and questionnaire colour as two variables influencing response rates in a mail survey. Journal of Applied Psychology 1974;59(4):535-6.

Mauz 2018 {published data only}

Mauz Elvira, Hoffmann Robert, Houben Robin, Krause Laura, Kamtsiuris Panagiotis, Goswald Antje. Mode Equivalence of Health Indicators Between Data Collection Modes and Mixed-Mode Survey Designs in Population-Based Health Interview Surveys for Children and Adolescents: Methodological Study. Journal of medical Internet research 2018;20(3):e64.

Maxwell 2009 {published data only}

Maxwell A E, Bastani R, Glenn B A, Mojica C M, Chang L C. An Experimental Test of the Effect of Incentives on Recruitment of Ethnically Diverse Colorectal Cancer Cases and Their First-Degree Relatives into a Research Study. CANCER EPIDEMIOLOGY BIOMARKERS & PREVENTION 2009;18(10):2620-5.

McCaffery 2019 {published data only}

McCaffery J, Mitchell A S, Fairhurst C, Cockayne S, Rodgers S, Relton C, et al. Does handwriting the name of a potential trial participant on an invitation letter improve recruitment rates? A randomised controlled study within a trial. F1000Research 2019;8:659.

McCambridge 2011 {published data only}

McCambridge J, Kalaitzaki E, White I R, Khadjesari Z, Murray E, Linke S, et al. Impact of Length or Relevance of Questionnaires on Attrition in Online Trials: Randomized Controlled Trial. JOURNAL OF MEDICAL INTERNET RESEARCH 2011;13(4):e96.

McColl 2003a {published data only}

McColl E, Eccles MP, Rousseau NS, Steen IN, Parkin DW, Grimshaw JM. From the generic to the condition-specific? Instrument order effects in quality of life assessment. Medical Care 2003a;7:777–90.

McColl 2003b {published data only}

McColl E, Eccles MP, Rousseau NS, Steen IN, Parkin DW, Grimshaw JM. From the generic to the condition-specific? Instrument order effects in quality of life assessment. Medical Care 2003b;7:777–90.

McConochie 1985 {published data only}

McConochie RM, Rankin CA. Effects of monetary premium variations on response/non response bias: representation of black and non black respondents in surveys of radio listening. Proceeding of the Section on Survey, American Statistical Association 1985;2:42-5.

McCormack 2013 {published data only}

McCormack LA. Effect of Small Monetary Incentive and Demographic Characteristics on Response Rate of Self-Administered Questionnaire Mailed to Rural Women. Online J Rural Res Policy 2013;8(1):1.

McCoy 2007 {published data only}

McCoy M, Hargie O. Effects of personalization and envelope color on response rate, speed and quality among a business population. Industrial Marketing Management 2007;36:799–809.

McDaniel 1980 {published data only}

McDaniel SW. The effect of monetary inducement on mailed questionnaire response quality. Journal of Marketing Research 1980;17:265-8.

McDaniel 1981 {published data only}

McDaniel SW. An investigation of respondent anonymity’s effect on mailed questionnaire response rate and quality. Journal of the Market Research Society 1981;23(3):150-60.

McGonagle 2017 {published data only}

McGonagle K A, Freedman V A. The Effects of a Delayed Incentive on Response Rates, Response Mode, Data Quality, and Sample Bias in a Nationally Representative Mixed Mode Study. FIELD METHODS 2017;29(3):221-37.

McKee 1992 {published data only}

McKee D. The effect of using a questionnaire identification code and message about non-response follow-up plans on mail survey response characteristics. Journal of the Market Research Society 1992;34(2):179-91.

McKenzie‐McHarg 2005 {published data only}

McKenzie-McHarg K, Tully L, Gates S, Ayers S, Brocklehurst P. Effect on survey response rate of hand written versus printed signature on a covering letter: randomised controlled trial. BMC Health Services Research 2005;5(52):1-5.

McKillip 1984 {published data only}

McKillip J, Lockhart DC. The effectiveness of cover-letter appeals. Journal of Social Psychology 1984;122:85-91.

McLaren 2000a {published data only}

McLaren B, Shelley J. Response rates of Victorian general practitioners to a mailed survey on miscarriage: randomised trial of a prize and two forms of introduction to the research. Australian and New Zealand Journal of Public Health 2000;24(4):360-4.

McLaren 2000b {published data only}

McLaren B, Shelley J. Response rates of Victorian general practitioners to a mailed survey on miscarriage: randomised trial of a prize and two forms of introduction to the research. Australian and New Zealand Journal of Public Health 2000;24(4):360-4.

McLean 2014 {published data only}

McLean S A, Paxton S J, Massey R, Mond J M, Rodgers B, Hay P J. Prenotification but not envelope teaser increased response rates in a bulimia nervosa mental health literacy survey: A randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2014;67(8):870-6.

Meadows 2000 {published data only}

Meadows KA, Greene T, Foster L, Beer S. The impact of different response alternatives on responders' reporting of health-related behaviour in a postal survey. Quality of Life Research 2000;9:385-91.

Meuleman 2017 {published data only}

Meuleman Bart, Langer Arnim, Blom Annelies G. Can Incentive Effects in Web Surveys Be Generalized to Non-Western Countries? Conditional and Unconditional Cash Incentives in a Web Survey of Ghanaian University Students. SOCIAL SCIENCE COMPUTER REVIEW 2017;36(2):231-50.

Millar 2011a {published data only}

Millar Morgan M, Dillman Don A. IMPROVING RESPONSE TO WEB AND MIXED-MODE SURVEYS. The Public Opinion Quarterly 2011;75(2):249-69.

Millar 2011b {published data only}

Millar Morgan M, Dillman Don A. IMPROVING RESPONSE TO WEB AND MIXED-MODE SURVEYS. The Public Opinion Quarterly 2011;75(2):249-69.

Millar 2019 {published data only}

Millar Morgan M, Elena Joanne W, Gallicchio Lisa, Edwards Sandra L, Carter Marjorie E, Herget Kimberly A, et al. The feasibility of web surveys for obtaining patient-reported outcomes from cancer survivors: a randomized experiment comparing survey modes and brochure enclosures. BMC medical research methodology 2019;19(1):208.

Miller 1994 {published data only}

Miller MM. The effects of cover letter appeal and non monetary incentives on university professors' response to a mail survey. Paper presented at the annual meeting of the American Educational Research Association 1994.

Mills 2019 {published data only}

Mills S. A $2 Bill or Two $1 Bills: An Experiment that Challenges Standard Protocol. FIELD METHODS 2019;31(3):230-40.

Mitchell 2011 {published data only}

Mitchell N, Hewitt C E, Torgerson D J, Grp Scoop Trial. A controlled trial of envelope colour for increasing response rates in older women. AGING CLINICAL AND EXPERIMENTAL RESEARCH 2011;23(3):236-40.

Mitchell 2012 {published data only}

Mitchell N, Hewitt C E, Lenaghan E, Platt E, Shepstone L, Torgerson D J, et al. Prior notification of trial participants by newsletter increased response rates: a randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2012;65(12):1348-52.

Mitchell 2021a {published data only}

Mitchell Alex S, Cook Liz, Dean Alexandra, Fairhurst Caroline, Torgerson David J, Northgraves Matthew, et al. An embedded randomised controlled retention trial ofpersonalised text messages compared to non-personalised text messages in an orthopaedic setting [version 1; peer review: 1 approved]. F1000Research 2021;9((Mitchell, Cook, Dean, Fairhurst, Torgerson, Reed) Department of Health Sciences, University of York, York Y010 5DD, United Kingdom(Northgraves) Hull Health Trials Unit, University of Hull, Hull HU6 7RU, United Kingdom(Reed) North Tyneside General Hospita):1-8.

Mitchell 2021b {published data only}

Mitchell A S, Cook L, Dean A, Fairhurst C, Northgraves M, Torgerson D J, et al. Using pens as an incentive for questionnaire return in an orthopaedic trial: an embedded randomised controlled retention trial. F1000Research 2021;9:321.

Mizes 1984 {published data only}

Mizes JS, Fleece EL, Roos C. Incentives for increasing return rates: magnitude levels, response bias, and format. Public Opinion Quarterly 1984;48(4):794-800.

Mockovak 2012 {published data only}

Mockovak W. The Impact of Visual Design in Survey Cover Letters on Response and Web Take‐Up Rates. U S Bureau of Labor Statistics 2012;https://www.bls.gov/osmr/research-papers/2011/pdf/st110040.pdf.

Mond 2004 {published data only}

Mond JM, Rodgers B, Hay PJ, Owen C, Beumont PJV. Mode of delivery, but not questionnaire length, affected response in an epidemiological study of eating-disordered behavior. Journal of Clinical Epidemiology 2004;57:1167–71.

Morgan 2017 {published data only}

Morgan A J, Rapee R M, Bayer J K. Increasing response rates to follow-up questionnaires in health intervention research: Randomized controlled trial of a gift card prize incentive. CLINICAL TRIALS 2017;14(4):381-6.

Morris 2013 {published data only}

Morris M, Edwards P, Doyle P, Maconochie N. Women in an infertility survey responded more by mail but preferred a choice: randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2013;66(2):226-35.

Morrison 2003 {published data only}

Morrison DS, Thomson H, Petticrew M. Effects of disseminating research findings on response rates in a community survey: a randomised controlled trial. Journal of Epidemiology and Community Health 2003;57:536-7.

Mortagy 1985 {published data only}

Mortagy AK, Howell JB, Waters WE. A useless raffle. Journal of Epidemiology and Community Health 1985;39:183-4.

Moses 2004 {published data only}

Moses SH, Clark TJ. Effect of prize draw incentive on the response rate to a postal survey of obstetricians and gynaecologists: a randomised controlled trial. BMC Health Services Research 2004;4(14):1-3.

Moss 1991 {published data only}

Moss VD, Worthen BR. Do personalization and postage make a difference on response rates to surveys of professional populations. Psychological Reports 1991;68:692-4.

Mullen 1987 {published data only}

Mullen P, Easling I, Nixon SA, Koester DR, Biddle AK. The cost-effectiveness of randomised incentive and follow-up contacts in a national mail survey of family physicians. Evaluation & the Health Professions 1987;10(2):232-45.

Mullner 1982 {published data only}

Mullner RM, Levy PS, Byre CS, Matthews D. Effects of characteristics of the survey instrument on response rates to a mail survey of community hospitals. Public Health Reports 1982;97(5):465-9.

Munoz 2017 {published data only}

Munoz R F, Leykin Y, Barrera A Z, Brown C H, Bunge E L. The impact of phone calls on follow-up rates in an online depression prevention study. Internet interventions 2017;8(101631612):10-4.

Murawski 1996 {published data only}

Murawski MM, Carroll NV. Direct mail performance of selected health related quality of life scales. Journal of Pharmacoepidemiology 1996;5(1):17-38.

Murdoch 2014 {published data only}

Murdoch M, Simon A B, Polusny M A, Bangerter A K, Grill J P, Noorbaloochi S, et al. Impact of different privacy conditions and incentives on survey response rate, participant representativeness, and disclosure of sensitive information: a randomized controlled trial. BMC MEDICAL RESEARCH METHODOLOGY 2014;14:90.

Murphy 1991 {published data only}

Murphy PM, Daley JM. Exploring the effects of postcard prenotification on industiral firms' response to mail surveys. Journal of the Market Research Society 1991;33(4):335-41.

Murphy 2020 {published data only}

Murphy Caitlin C, Craddock Lee Simon J, Geiger Ann M, Cox John V, Ahn Chul, Nair Rasmi, et al. A randomized trial of mail and email recruitment strategies for a physician survey on clinical trial accrual. BMC medical research methodology 2020;20(1):123.

Myers 1969 {published data only}

Myers JH, Haug AF. How a preliminary letter affects mail survey returns and costs. Journal of Advertising Research 1969;9(3):37-9.

Myhre 2019a {published data only}

Myhre J B, Andersen L F, Holvik K, Astrup H, Kristiansen A L. Means of increasing response rates in a Norwegian dietary survey among infants - results from a pseudo-randomized pilot study. BMC MEDICAL RESEARCH METHODOLOGY 2019;19:144.

Myhre 2019b {published data only}

Myhre J B, Andersen L F, Holvik K, Astrup H, Kristiansen A L. Means of increasing response rates in a Norwegian dietary survey among infants - results from a pseudo-randomized pilot study. BMC MEDICAL RESEARCH METHODOLOGY 2019;19:144.

Nagata 1995 {published data only}

Nagata C, Hara S, Shimizu H. Factors affecting response to mail questionnaire: research topics, questionnaire length, and non-response bias. Journal of Epidemiology 1995;5(5):81-5.

Nakai 1997 {published data only}

Nakai S, Hashimoto S, Murakami Y, Hayashi M, Manabe K, Noda H. Response rates and non-response bias in a health-related mailed survey. Nippon-Koshu-Eisei-Zasshi 1997;44(3):184-91.

Nakash 2007 {published data only}

Nakash Rachel Anne. A study of response and non-response to postal questionnaire follow-up in clinical trials. Thesis (Ph.D.) - University of Warwick, 2007. 2007:1.

Nakazawa 2020 {published data only}

Nakazawa Y, Takeuchi E, Miyashita M, Sato K, Ogawa A, Kinoshita H, Kizawa Y, Morita T, Kato M. A Population-based Mortality Follow-Back Survey Evaluating Good Death for Cancer and Non-cancer Patients: A Randomized Feasibility Study. Journal of pain and symptom management 2020;61(1):42-53.

Napoles‐Springer 2004 {published data only}

Napoles-Springer AM, Fongwa MN, Stewart AL, Gildengorin G, Perez-Stable EJ. The effectiveness of an advance notice letter on the recruitment of African Americans and Whites for a mailed patient satisfaction survey. Journal of Aging & Health 2004;16(5 Suppl):124S-36S.

Nathenson 2019 {published data only}

Nathenson R A, Supovitz J. Variation in Motivational Appeals to Survey Completion: Lessons from a Randomized Experiment with Teachers. JOURNAL OF RESEARCH ON EDUCATIONAL EFFECTIVENESS 2019;12(2):307-31.

Nederhof 1982 {published data only}

Nederhof AJ. Effects of preliminary contacts on volunteering in mail surveys. Perceptual and Motor Skills 1982;54:1333-4.

Nederhof 1983a {published data only}

Nederhof AJ. Effects of repetition and consistency of personalization treatments on response rate in mail surveys. Social Science Research 1983a;12:1-9.

Nederhof 1983b {published data only}

Nedefhof AJ. Effects of repetition and consistency of personalization treatments on response rate in mail surveys. Social Science Research 1983b;12:1-9.

Nederhof 1988 {published data only}

Nedefhof AJ. Effects of a final telephone reminder and questionnaire cover design in mail surveys. Social Science Research 1988;17:353-61.

Neider 1981a {published data only}

Neider L, Sugrue P. Personalization as a response inducement technique in mail surveys. American Institute of Decision Sciences 1981;13:238-9.

Neider 1981b {published data only}

Neider L, Sugrue P. Personalization as a response inducement technique in mail surveys. American Institute of Decision Sciences 1981;13:238-9.

Nesrallah 2014 {published data only}

Nesrallah Gihad, Barnieh Lianne, Manns Braden, Clase Catherine, Mendelssohn David, Guyatt Gordon. A charitable donation incentive did not increase physician survey response rates in a randomized trial. Journal of clinical epidemiology 2014;67(4):482-3.

Nevin 1975a {published data only}

Nevin JR, Ford NM. Effects of a deadline and veiled threat on mail survey responses. Journal of Applied Psychology 1975;61(1):116-8.

Nevin 1975b {published data only}

Nevin JR, Ford NM. Effects of a deadline and veiled threat on mail survey responses. Journal of Applied Psychology 1975;61(1):116-8.

Newby 2003 {published data only}

Newby R, Watson J, Woodliff D. SME survey methodology: response rates, data quality, and cost effectiveness. Entrepreneurship Theory and Practice 2003;28(2):163-72.

Newland 1977 {published data only}

Newland CA, Waters WE, Standford AP, Batchelor BG. A study of mail survey method. International Journal of Epidemiology 1977;6(1):65-7.

Nichols 1966 {published data only}

Nichols RC, Meyer MA. Timing postcard follow-ups in mail questionnaire surveys. Public Opinion Quarterly 1966;30:3006-7.

Nichols 1988 {published data only}

Nichols S, Waters WE, Woolaway M, Hamilton-Smith MB. Evaluation of the effectiveness of a nutritional health education leaflet in changing public knowledge and attitudes about eating and health. Journal of Human Nutrition and Dietetics 1988;1:233-8.

Nicolaas 2015 {published data only}

Nicolaas G, Smith P, Pickering K, Branson C. Increasing response rates in postal surveys while controlling costs: an experimental investigation. Social Research Practice 2015;1:3-16.

Noel 2018 {published data only}

Noel HarmoniJoie, Huang Alison R. The Effect of Varying Incentive Amounts on Physician Survey Response. EVALUATION & THE HEALTH PROFESSIONS 2018;42(1):71-81.

O'Connor 2011 {published data only}

O'Connor M. The challenge of recruiting control groups. An experiment of different recruitment models in the control group of a clinical psychological postal survey. QUALITY & QUANTITY 2011;45(4):743-50.

Ogborne 1986 {published data only}

Ogbourne AC, Rush B, Fondacaro R. Dealing with nonrespondents in a mail survey of professionals. Evaluation & the Health Professions 1986;9(1):121-8.

Olivarius 1995 {published data only}

Olivarius N de F, Andreasen AH. Day-of-the-week effect on doctors' response to a postal questionnaire. Scandinavian Journal of Primary Health Care 1995;13:65-7.

Olsen 2012 {published data only}

Olsen Frank, Abelsen Birgit, Olsen Jan Abel. Improving response rate and quality of survey data with a scratch lottery ticket incentive. BMC Medical Research Methodology 2012;12(1):52.

Osborne 1996 {published data only}

Osborne MO, Ward J, Boyle C. Effectiveness of telephone prompts when surveying general practitioners: a randomised trial. Australian Family Physician 1996;25(1):S41-3.

Pace 2020 {published data only}

Pace Lydia E, Lee Yeonsoo S, Tung Nadine, Hamilton Jada G, Gabriel Camila, Raja Sahitya C, et al. Comparison of up-front cash cards and checks as incentives for participation in a clinician survey: a study within a trial. BMC medical research methodology 2020;20(1):210.

Paolillo 1984 {published data only}

Paolillo JG, Lorenzi P. Monetary incentives and mail questionnaire response rates. Journal of Advertising 1984;131:46-8.

Parasuraman 1981 {published data only}

Parasuraman A. Impact of cover letter detail on response patterns in a mail survey. American Institute of Decision Science 1981;13th Meeting:289-91.

Parker 2019 {published data only}

A Parker, S Brealey, A Keding, L Kottam, A Mitchell, M Northgraves, PP Sarathy, C Welch, A Rangan. Timing of text message reminders to increase trial participant response to postal questionnaires: An embedded randomized trial. Trials 2019;20(Supplement 1):579.

Parkes 2000a {published data only}

Parkes R, Kreiger N, James B, Johnson KC. Effects on subject response of information brochures and small cash incentives in a mail-based case-control study. Annals of Epidemiology 2000;10:117-24.

Parkes 2000b {published data only}

Parkes R, Kreiger N, James B, Johnson KC. Effects on subject response of information brochures and small cash incentives in a mail-based case-control study. Annals of Epidemiology 2000;10:117-24.

Parsons 1972a {published data only}

Parsons RJ, Medford TS. The effect of advance notice in mail surveys of homogeneous groups. Public Opinion Quarterly 1972;36:258-9.

Parsons 1972b {published data only}

Parsons RJ, Medford TS. The effect of advance notice in mail surveys of homogenous groups. Public Opinion Quarterly 1972;36:258-9.

Patrick 2013 {published data only}

Patrick Megan E, Singer Eleanor, Boyd Carol J, Cranford James A, McCabe Sean Esteban. Incentives for college student participation in web-based substance use surveys. Addictive behaviors 2013;38(3):1710-4.

Patrick 2018 {published data only}

Patrick Megan E, Couper Mick P, Laetz Virginia B, Schulenberg John E, O'Malley Patrick M, Johnston Lloyd D, et al. A Sequential Mixed-Mode Experiment in the U.S. National Monitoring the Future Study. Journal of survey statistics and methodology 2018;6(1):72-97.

Paul 2005 {published data only}

Paul CL, Walsh RA, Tzelepis F. A monetary incentive increases postal survey response rates for pharmacists. Journal of Epidemiology and Community Health 2005;59:1099-101.

Pearson 2003 {published data only}

Pearson J, Levine RA. Salutations and Response Rates to Online Surveys. Association for Survey Computing, Fourth International Conference on the Impact of Technology on the Survey Process 2003;1:1-9.

Peck 1981 {published data only}

Peck JK, Dresch SP. Financial incentives, survey response, and sample representativeness: does money matter? Review of Public Data Use 1981;9:245-66.

Pedersen 2016 {published data only}

Pedersen M J, Nielsen C V. Improving Survey Response Rates in Online Panels: Effects of Low-Cost Incentives and Cost-Free Text Appeal Interventions. SOCIAL SCIENCE COMPUTER REVIEW 2016;34(2):229-43.

Pedrana 2008 {published data only}

Pedrana A, Hellard M, Giles M. Registered post achieved a higher response rate than normal mail - A randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2008;61(9):896-9.

Pejtersen 2020 {published data only}

Pejtersen JH. The effect of monetary incentive on survey response for vulnerable children and youths: A randomized controlled trial. PLOS ONE 2020;15(5):e0233025.

Perneger 1993 {published data only}

Perneger TV, Etter J-F, Rougemont A. Randomized trial of use of a monetary incentive and a reminder card to increase the response rate to a mailed questionnaire. American Journal of Epidemiology 1993;138(9):714-22.

Perry 1974 {published data only}

Perry N. Postage combinations in postal questionnaire surveys - another view. Journal of the Market Research Society 1974;16(3):245-6.

Peters 1998 {published data only}

Peters TJ, Harvey IM, Bachmann MO, Eachus JI. Does requesting sensitive information on postal questionnaires have an impact on response rates? A randomised controlled trial in the south west of England. Journal of Epidemiology and Community Health 1998;52:130.

Peterson 1975 {published data only}

Peterson RA. An experimental investigation of mail survey responses. Journal of Business Research 1975;3(3):199-210.

Petrovčič 2016 {published data only}

Petrovčič Andraž, Petrič Gregor, Lozar Manfreda Katja. The effect of email invitation elements on response rate in a web survey within an online community. Computers in Human Behavior 2016;56:320-9.

Phillips 1951 {published data only}

Phillips WM. Weaknesses of the mail questionnaire: a methodological study. Sociology & Social Research 1951;35:260-7.

Pirotta 1999 {published data only}

Pirotta M, Gunn J, Farish S, Karabatsos G. Primer postcard improves postal survey response rates. Australian and New Zealand Journal of Public Health 1999;23(2):196-7.

Pit 2013 {published data only}

Pit S W, Hansen V, Ewald D. A small unconditional non-financial incentive suggests an increase in survey response rates amongst older general practitioners (GPs): a randomised controlled trial study. BMC FAMILY PRACTICE 2013;14:108.

Poe 1988 {published data only}

Poe GS, Seeman I, McLaughlin J, Mehl E, Dietz M. 'Don't know' boxes in factual questions in a mail questionnaire. Public Opinion Quarterly 1988;52:212-22.

Porter 2003a {published data only}

Porter SR, Whitcomb ME. The impact of lottery incentives on student survey response rates. Research in Higher Education 2003;44(4):389-407.

Porter 2003b {published data only}

Porter SR, Whitcomb ME. The impact of contact type on web survey response rates. Public Opinion Quarterly 2003b;67:579–88.

Porter 2005a {published data only}

Porter SR, Whitcomb ME. E-mail subject lines and their effect on web survey viewing and response. Social Science Computer Review 2005;23:280-7.

Porter 2005b {published data only}

Porter SR, Whitcomb ME. E-mail subject lines and their effect on web survey viewing and response. Social Science Computer Review 2005;23:280-7.

Porter S 2003b {published data only}

Porter SR, Whitcomb ME. The impact of contact type on web survey response rates. Public Opinion Quarterly 2003b;67:579–88.

Pourjalali 1994 {published data only}

Pourjalali H, Kimbrell J. Effects of four instrumental variables on survey response. Psychological Reports 1994;75:895-8.

Powers 1982 {published data only}

Powers DE, Alderman DL. Feedback as an incentive for responding to a mail questionnaire. Research in Higher Education 1982;17(3):207-11.

Pressley 1977 {published data only}

Pressley MM, Tullar WL. A factor interactive investigation of mail survey response rates from a commercial population. Journal of Marketing Research 1977;14:108-11.

Pressley 1978 {published data only}

Pressley MM. Care needed when selecting response inducements in mail surveys of commercial populations. Journal of the Academy of Marketing Science 1978;6(4):336-43.

Pressley 1985 {published data only}

Pressley MM, Dunn MG. A factor-interactive experimental investigation of inducing response to questionnaires mailed to commercial populations. AMA Educators Conference Proceedings 1985;14(1):356-61.

Price 1996 {published data only}

Price JH, Easton A, Kandakai T, Oden L. Race-specific versus general stamps on African-American women's survey return rates. Perceptual and Motor Skills 1996;82:928-30.

Price 2003 {published data only}

Price JH, Dake JA, Akpanudo S, Kleinfelder J. The effect of survey return rates of having a signed or unsigned postcard as the third wave mailing. Psychological Reports 2003;92(2):1099-102.

Price 2010 {published data only}

Price James H, Khubchandani Jagdish, Bryant Michele, Rickard Megan, Hendershot Candace, Thompson Amy. Survey return rates for multiple-authored versus single-authored covering letters. Psychological reports 2010;107(1):209-12.

Price 2014 {published data only}

Price A M H, Coates C, Symeonides C, Hiscock H, Smith L, York E, et al. Chocolate frogs do not increase completion of parent survey: Randomised study. JOURNAL OF PAEDIATRICS AND CHILD HEALTH 2014;50(11):866-8.

Pucel 1971 {published data only}

Pucel DJ, Nelson HF, Wheeler DN. Questionnaire follow-up returns as a function of incentives and responder characteristics. Vocational Guidance Quarterly 1971;March:188-93.

Puffer 2004 {published data only}

Puffer S, Porthouse J, Birks Y, Morton V, Torgerson D. Increasing response rates to postal questionnaires: a randomised trial of variations in design. Journal of Health Services Research & Policy 2004;9(4):213–7.

Rach 2020 {published data only}

Rach S, Gunther K, Hadeler B. Participants who were difficult to recruit at baseline are less likely to complete a follow-up questionnaire - results from the German National Cohort. BMC MEDICAL RESEARCH METHODOLOGY 2020;20(1):187.

Rath 2017 {published data only}

Rath J M, Williams V F, Villanti A C, Green M P, Mowery P D, Vallone D M. Boosting Online Response Rates Among Nonresponders: A Dose of Funny. SOCIAL SCIENCE COMPUTER REVIEW 2017;35(5):619-32.

Recklitis 2009 {published data only}

Recklitis C J, Campbell E G, Kutner J S, Bober S L. Money talks: non-monetary incentive and Internet administration fail to increase response rates to a physician survey. JOURNAL OF CLINICAL EPIDEMIOLOGY 2009;62(2):224-6.

Rego 2020 {published data only}

Rego Ryan, Watson Samuel, Ishengoma Philbert, Langat Philemon, Otieno Hezekiah Pireh, Lilford Richard. Effectiveness of SMS messaging for diarrhoea measurement: a factorial cross-over randomised controlled trial. BMC medical research methodology 2020;20(1):174.

Reinisch 2016 {published data only}

Reinisch John F, Yu Daniel C, Li Wai-Yee. Getting a Valid Survey Response From 662 Plastic Surgeons in the 21st Century. Annals of plastic surgery 2016;76(1):3-5.

Renfroe 2002 {published data only}

Renfroe EG, Heywood G, Foreman L, Schron E, Powell J, Baessler C, et al, for the AVID Coordinators and Investigators. The end-of-study patient survey: methods influencing response rate in the AVID Trial. Controlled Clinical Trials 2002;23:521-33.

Riesenberg 2006 {published data only}

Riesenberg LA, Rosebaum P, Stick SL. Unexpected mailed survey response rates. Family Medicine 2006;38(2):83.

Rikard‐Bell 2000 {published data only}

Rikard-Bell G, Ward J. Maximizing response rates to a survey of dentists: a randomized trial. Australian Dental Journal 2000;45(1):46-8.

Rimm 1990 {published data only}

Rimm EB, Stampfer MJ, Colditz GA, Giovannuci E, Willet WC. Effectiveness of various mailing strategies among nonrespondents in a prospective cohort study. American Journal of Epidemiology 1990;131(6):1068-71.

Robb 2017 {published data only}

Robb K A, Gatting L, Wardle J. What impact do questionnaire length and monetary incentives have on mailed health psychology survey response? BRITISH JOURNAL OF HEALTH PSYCHOLOGY 2017;22(4):671-85.

Roberts 1978 {published data only}

Roberts RE, McCrory OF, Forthofer RN. Further evidence on using a deadline to stimulate responses to a mail survey. Public Opinion Quarterly 1978;42:407-10.

Roberts 1993 {published data only}

Roberts H, Pearson JC, Dengler R. Impact of a postcard versus a questionnaire as a first reminder in a postal lifestyle survey. Journal of Epidemiology and Community Health 1993;47:334-5.

Roberts 1994 {published data only}

Roberts I, Coggan C, Fanslow J. Epidemiological methods: the effect of envelope type on response rates in an epidemiological study of back pain. Aust NZ Journal of Occupational Health and Safety 1994;10(1):55-7.

Roberts 2000 {published data only}

Roberts P-J, Roberts C, Sibbald B, Torgerson DJ. The effect of a direct payment or a lottery on questionnaire response rates: a randomised controlled trial. Journal of Epidemiology and Community Health 2000;54:71-2.

Roberts 2004 {published data only}

Roberts LM, Wilson S, Roalfe A, Bridge P. A randomised controlled trial to determine the effect on response of including a lottery incentive in health surveys. BMC Health Services Research 2004;4(30):1-8.

Robertson 1978 {published data only}

Robertson DH, Bellenger DN. A new method of increasing mail survey responses: Contributions to charity. Journal of Marketing Research 1978;15:632-3.

Robertson 2005 {published data only}

Robertson J, Walkom EJ, McGettigan P. Response rates and representativeness: a lottery incentive improves physician survey response rates. Pharmacoepidemiology and Drug Safety 2005;14:571-7.

Rodgers 2018 {published data only}

Rodgers S, Sbizzera I, Cockayne S, Fairhurst C, Lamb S E, Vernon W, et al. A study update newsletter or Post-it® note did not increase postal questionnaire response rates in a falls prevention trial: an embedded randomised factorial trial. f1000research 2018;16(7):1083.

Rolnick 1989 {published data only}

Rolnick SJ, Gross CR, Garrard J, Gibson RW. A comparison of response rate, data quality, and cost in the collection of data on sexual history and personal behaviours. American Journal of Epidemiology 1989;129(5):1052-61.

Romney 1993 {unpublished data only}

Romney VA. A comparison of responses to open-ended and closed ended items on a state-level community education needs assessment instrument. Doctoral Dissertation 1993.

Ronckers 2004 {published data only}

Ronckers C, Land C, Hayes R, Verdunijn P, Van LeeUwen F. Factors impacting questionnaire response in a Dutch retrospective cohort study. Annals of Epidemiology 2004;14(1):66–72.

Roscoe 1975 {published data only}

Roscoe AM, Lang D, Sheth JN. Follow-up methods, questionnaire length, and market differences in mail surveys. Journal of Marketing 1975;39:20-7.

Rose 2007a {published data only}

Rose DS, Sidle SD, Griffith KH. A penny for your thoughts. Monetary incentives improve response rates for company-sponsored employee surveys. Organizational Research Methods 2007a;10(2):225-40.

Rose 2007b {published data only}

Rose DS, Sidle SD, Griffith KH. A penny for your thoughts. Monetary incentives improve response rates for company-sponsored employee surveys. Organizational Research Methods 2007;10(2):225-40.

Rosoff 2005a {published data only}

Rosoff PM, Werner C, Clipp EC, Guill AB, Bonner M, Demark-Wahnefried W. Response rates to a mailed survey targeting childhood cancer survivors: A comparison of conditional versus unconditional incentives. Cancer Epidemiology, Biomarkers & Prevention 2005a;14(5):1330-2.

Rosoff 2005b {published data only}

Rosoff PM, Werner C, Clipp EC, Guill AB, Bonner M, Demark-Wahnefried W. Response rates to a mailed survey targeting childhood cancer survivors: A comparison of conditional versus unconditional incentives. Cancer Epidemiology, Biomarkers & Prevention 2005b;14(5):1330-2.

Rosoff 2005c {published data only}

Rosoff PM, Werner C, Clipp EC, Guill AB, Bonner M, Demark-Wahnefried W. Response rates to a mailed survey targeting childhood cancer survivors: A comparison of conditional versus unconditional incentives. Cancer Epidemiology, Biomarkers & Prevention 2005c;14(5):1330-2.

Roszkowski 1990a {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990b {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990c {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990d {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990e {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990f {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990g {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990h {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990i {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990j {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990k {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990l {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990m {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Roszkowski 1990n {published data only}

Roszkowski MJ, Bean AG. Believe it or not! Longer questionnaires have lower response rates. Journal of Business and Psychology 1990;4(4):495-509.

Rucker 1979a {published data only}

Rucker MH, Arbaugh JE. A comparison of matrix questionnaires with standard questionnaires. Educational and Psychological Measurement 1979;39:637-43.

Rucker 1979b {published data only}

Rucker MH, Arbaugh JE. A comparison of matrix questionnaires with standard questionnaires. Educational and Psychological Measurement 1979;39:637-43.

Rucker 1984 {published data only}

Rucker M et al. Personalization of mail surveys: too much of a good thing? Educational and Psychological Measurement 1984;44(4):893-905.

Russell 2003 {published data only}

Russell ML, Mutasingwa DR, Verhoef MJ, Injeyan HS. Effect of a monetary incentive on chiropractors’ response rate and time to respond to a mail survey. Journal of Clinical Epidemiology 2003;56:1027–8.

Ryu 2006 {published data only}

Ryu E, Couper MP, Marans RW. Survey incentives: cash vs. in-kind; face-to-face vs. mail; response rate vs. nonresponse error. International Journal of Public Opinion Research 2006;18(1):89-106.

Saal 2005 {published data only}

Saal D, Nuebling M, Husemann Y, Heidegger T. Effect of timing on the response to postal questionnaires concerning satisfaction with anaesthesia care. British Journal of Anaesthesia 2005;94(2):206–10.

Sahlqvist 2011 {published data only}

Sahlqvist Shannon, Song Yena, Bull Fiona, Adams Emma, Preston John, Ogilvie David, et al. Effect of questionnaire length, personalisation and reminder type on response rate to a complex postal survey: randomised controlled trial. BMC medical research methodology 2011;11(100968545):62.

Sakshaug 2019 {published data only}

Sakshaug Joseph W, Vicari Basha, Couper Mick P. Paper, e-mail, or both? Effects of contact mode on participation in a web survey of establishments. Social Science Computer Review 2019;37(6):750-65.

Salim Silva 2002 {published data only}

Salim Silva M, Smith WT, Bammer G. Telephone reminders are a cost effective way to improve responses in postal health surveys. Journal of Epidemiology and Community Health 2002;56:115-8.

Sallis 1984 {published data only}

Sallis JF, Fortmann SP, Solomon DS, Farquhar JW. Increasing returns of physician surveys. American Journal of Public Health 1984;74(9):1043.

Salvesen 1992 {published data only}

Salvesen K, Vatten L. Effect of a newspaper article on the response to a postal questionnaire. Journal of Epidemiology and Community Health 1992;46:86.

Sang‐Wook 2005 {published data only}

Sang-Wook Y, Hong JS, Ohr H, Yi JJ. A comparison of response rate and time according to the survey methods used: a randomized controlled trial. European Journal of Epidemiology 2005;20:131–5.

Satia 2005 {published data only}

Satia J A, Galanko J A, Rimer B K. Methods and strategies to recruit African Americans into cancer prevention surveillance studies. CANCER EPIDEMIOLOGY BIOMARKERS & PREVENTION 2005;14(3):718-21.

Sauerland 2002 {published data only}

Sauerland S, Neugebauer EAM. An experiment of mailing physician surveys on two different issues in joint or separate mail. Journal of Clinical Epidemiology 2002;55:1046-8.

Schmidt 2005 {published data only}

Schmidt JB, Calantone RJ, Griffin A, Montoya-Weiss MM. Do certified mail third-wave follow-ups really boost response rates and quality? Marketing Letters 2005;16(2):129-41.

Schmuhl 2010 {published data only}

Schmuhl P, Van Duker H, Gurley K L, Webster A, Olson L M. Reaching emergency medical services providers: is one survey mode better than another? Prehospital Emergency Care 2010;14(3):361-9.

Schwartzenberger 2017 {published data only}

Schwartzenberger Justin, Presson Angela, Lyle Adam, O'Farrell Andrew, Tyser Andrew R. Remote Collection of Patient-Reported Outcomes Following Outpatient Hand Surgery: A Randomized Trial of Telephone, Mail, and E-Mail. The Journal of hand surgery 2017;42(9):693-9.

Schweitzer 1995 {published data only}

Schweitzer M, Asch D. Timing payments to subjects of mail surveys: cost-effectiveness and bias. Journal of Clinical Epidemiology 1995;48(11):1325-9.

Scott 1957 {published data only}

Scott FG. Mail questionnaires used in a study of older women. Sociology and Social Research 1957;41:281-4.

Scott 2011 {published data only}

Scott A, Jeon S H, Joyce C M, Humphreys J S, Kalb G, Witt J, et al. A randomised trial and economic evaluation of the effect of response mode on response rate, response bias, and item non-response in a survey of doctors. BMC MEDICAL RESEARCH METHODOLOGY 2011;11:126.

Sebo 2017 {published data only}

Sebo P, Maisonneuve H, Cerutti B, Fournier JP, Senn N, Haller DM. Rates, Delays, and Completeness of General Practitioners' Responses to a Postal Versus Web-Based Survey: A Randomized Trial. JOURNAL OF MEDICAL INTERNET RESEARCH 2017;19(3):e83.

See Tai 1997 {published data only}

See Tai S, Nazareth I, Haines A, Jowett C. A randomized trial of the impact of telephone and recorded delivery reminders on the response rate to research questionnaires. Journal of Public Health Medicine 1997;19(2):219-21.

Severi 2011a {published data only}

Severi E, Free C, Knight R, Robertson S, Edwards P, Hoile E. Two controlled trials to increase participant retention in a randomized controlled trial of mobile phone-based smoking cessation support in the United Kingdom. CLINICAL TRIALS 2011;8(5):654-60.

Severi 2011b {published data only}

Severi E, Free C, Knight R, Robertson S, Edwards P, Hoile E. Two controlled trials to increase participant retention in a randomized controlled trial of mobile phone-based smoking cessation support in the United Kingdom. CLINICAL TRIALS 2011;8(5):654-60.

Shackleton 1980 {published data only}

Shackleton VJ, Wild JM, Wolffe M. Screening optometric patients by questionnaire: methods of improving response. American Journal of Optometry and Physiological Optics 1980;57(6):404-6.

Shah 2001 {published data only}

Shah S, Harris TJ, Rink E, DeWilde S, Victor CR, Cook DG. Do income questions and seeking consent to link medical records reduce survey response rates? A randomised controlled trial among older people. British Journal of General Practice 2001;51:223-5.

Shahar 1993 {published data only}

Shahar E, Bisgard KM, Folsom AR. Response to mail surveys: effect of a request to explain refusal to participate. Epidemiology 1993;4:480-2.

Sharp 2006 {published data only}

Sharp L, Cochran C, Cotton SC, Gray NM, Gallagher ME. Enclosing a pen with a postal questionnaire can significantly increase the response rate. Journal of Clinical Epidemiology 2006;59:747–54.

Shaw 2001 {published data only}

Shaw MJ, Beebe TJ, Jensen HL, Adlis SA. The use of monetary incentives in a community survey: Impact on response rates, data quality, and cost. Health Services Research 2001;35(6):1339-46.

Sheikh 1982 {published data only}

Sheikh K. Response to postal questionnaire: the effects of enquiry about earnings. International Review of Applied Psychology 1982;31:345-9.

Shin 1992 {unpublished data only}

Shin E. An experimental study of techniques to improve response rates of mail questionnaire. Utah State University 1992.

Shiono 1991 {published data only}

Shiono PH, Klebanoff MA. The effect of two mailing strategies on the response to a survey of physicians. American Journal of Epidemiology 1991;134(5):539-42.

Signorelli 2021 {published data only}

Signorelli Christina, Wakefield Claire E, McLoone Jordana K, Mateos Marion K, Aaronson Neil K, Lavoipierre Ange, et al. A cost-effective approach to increasing participation in patient-reported outcomes research in cancer: A randomized trial of video invitations. International journal of cancer 2021;148(4):971-80.

Simon 1967a {published data only}

Simon R. Responses to personal and form letters in mail surveys. Journal of Advertising Research 1967;7:28-30.

Simon 1967b {published data only}

Simon R. Responses to personal and form letters in mail surveys. Journal of Advertising Research 1967;7:28-30.

Simon 1967c {published data only}

Simon R. Responses to personal and form letters in mail surveys. Journal of Advertising Research 1967;7:28-30.

Sizmur 2019 {published data only}

Sizmur Steve, Roth Firona. Testing interventions to improve response to a National Health Service Staff Survey. Health Services Management Research 2019;32(3):124-9.

Skinner 1984 {published data only}

Skinner SJ, Ferrell OC, Pride WM. Personal and nonpersonal incentives in mail surveys: immediate versus delayed inducements. Academy of Marketing Science 1984;12(1):106-14.

Sletto 1940 {published data only}

Sletto R. Pretesting of questionnaires. American Sociological Review 1940;5:193-200.

Sloan 1997 {published data only}

Sloan M, Kreiger N, James B. Improving response rates among doctors: randomised trial. BMJ 1997;315:1136.

Smith 1985 {published data only}

Smith WCS, Crombie IK, Campion PD, Knox JDE. Comparison of response rates to a postal questionnaire from a general practice and a research unit. British Medical Journal 1985;291:1483-5.

So 2018 {published data only}

So R, Shinohara K, Aoki T, Tsujimoto Y, Suganuma A M, Furukawa T A. Effect of Recruitment Methods on Response Rate in a Web-Based Study for Primary Care Physicians: Factorial Randomized Controlled Trial. JOURNAL OF MEDICAL INTERNET RESEARCH 2018;20(2):e28.

Solnick 2020 {published data only}

Solnick Rachel, Nogee Daniel P, Boatright Dowin H, Jarou Zach. The effect of monetary incentives on survey completion by emergency medicine trainees: A randomized trial. Academic Emergency Medicine 2020;27(Supplement 1):S198-9.

Spry 1989a {published data only}

Spry VM, Hovell MF, Sallis JG, Hofsteter CR, Elder JP, Molgaard CA. Recruiting survey respondents to mailed surveys: controlled trials of incentives and prompts. American Journal of Epidemiology 1989;130(1):166-72.

Spry 1989b {published data only}

Spry VM, Hovell MF, Sallis JG, Hofsteter CR, Elder JP, Molgaard CA. Recruiting survey respondents to mailed surveys: controlled trials of incentives and prompts. American Journal of Epidemiology 1989;130(1):166-72.

Spry 1989c {published data only}

Spry VM, Hovell MF, Sallis JG, Hofsteter CR, Elder JP, Molgaard CA. Recruiting survey respondents to mailed surveys: controlled trials of incentives and prompts. American Journal of Epidemiology 1989;130(1):166-72.

Stafford 1966 {published data only}

Stafford JE. Influence of preliminary contact on mail returns. Journal of Marketing Research 1966;3:410-1.

Stange 2011 {published data only}

Stange J P, Zyzanski S J. The Effect of a College Pen Incentive on Survey Response Rate Among Recent College Graduates. EVALUATION REVIEW 2011;35(1):93-9.

Stapulonis 2004 {published data only}

Stapulonis RA, Marsh S, Markesich J. Incentives with low-income populations: an experiment with merchant point-of-sale (POS) cards. Paper presented at the Annual Conference of the American Association for Public Opinion Research, Phoenix, Arizona 2004.

Starr 2015 {published data only}

Starr K, McPherson G, Forrest M, Cotton SC. SMS text pre-notification and delivery of reminder e-mails to increase response rates to postal questionnaires: A factorial design, randomised, controlled trial. Trials 2015;8(16):295.

Stem 1984a {published data only}

Stem DE, Steinhorst RK. Telephone interview and mail questionnaire applications of the randomized response model. Journal of the American Statistical Association 1984a;79(387):555-64.

Stem 1984b {published data only}

Stem DE, Steinhorst RK. Telephone interview and mail questionnaire applications of the randomized response model. Journal of the American Statistical Association 1984a;79(387):555-64.

Stevens 1975 {published data only}

Stevens RE. Does precoding mail questionnaires affect response rates. Public Opinion Quarterly 1975;38:621-2.

Stolzmann 2019 {published data only}

Stolzmann K, Meterko M, Miller C J, Belanger L, Seibert M N, Bauer M S. Survey Response Rate and Quality in a Mental Health Clinic Population: Results from a Randomized Survey Comparison. JOURNAL OF BEHAVIORAL HEALTH SERVICES & RESEARCH 2019;46(3):521-32.

Streiff 2001 {published data only}

Streiff MB, Dundes L, Spivak JL. A mail survey of United States hematologists and oncologists: a comparison of business reply versus stamped return envelopes. Journal of Clinical Epidemiology 2001;54:430-2.

Subar 2001 {published data only}

Subar AF, Ziegler RG, Thompson FE, Johnson CC, Weissfeld JL, Reding D, et al. Is shorter always better? Relative importance of questionnaire length and cognitive ease on response rates and data quality for two dietary questionnaires. American Journal of Epidemiology 2001;153:404-9.

Sutton 1992 {published data only}

Sutton RJ, Zeitz LL. Multiple prior notifications, personalization, and reminder surveys. Marketing Research 1992;4:14-21.

Suzer‐Gurtekin 2019 {published data only}

Suzer-Gurtekin Z T, Elkasabi M, Lepkowski J M, Liu M, Curtin R. Randomized experiments for web-mail surveys conducted using address-based samples of the general population. In: Experimental Methods in Survey Research: Techniques that Combine Random Sampling with Random Assignment. Wiley, 2019:275-89.

Svensson 2012 {published data only}

Svensson M, Svensson T, Hansen A W, Lagerros Y T. The effect of reminders in a web-based intervention study. EUROPEAN JOURNAL OF EPIDEMIOLOGY 2012;27(5):333-40.

Svoboda 2001 {unpublished data only}

Svoboda P. A comparison of two questionnaires for assessing outcome after head injury in the Czech Republic. unpublished.

Swan 1980 {published data only}

Swan JE, Epley DE, Burns WL. Can follow-up response rates to a mail survey be increased by including another copy of the questionnaire? Psychological Reports 1980;47:103-6.

Szelényi 2005 {published data only}

Szelényi Katalin, Bryant Alyssa N, Lindholm Jennifer A. What Money Can Buy: Examining the effects of prepaid monetary incentives on survey response rates among college students. Educational Research and Evaluation 2005;11(4):385-404.

Szirony 2002 {published data only}

Szirony TA, Price JH, Telljohann SK, Wolfe E. Survey return rates using a covering letter signed by a graduate student or faculty member. Psychological Reports 2002;91:1174-6.

Tai 2018 {published data only}

Tai Xiaochen, Smith Alanna M, McGeer Allison J, Dubé Eve, Holness Dorothy Linn, Katz Kevin, et al. Comparison of response rates on invitation mode of a web-based survey on influenza vaccine adverse events among healthcare workers: a pilot study. BMC Medical Research Methodology 2018;18(1):N.PAG.

Tamayo‐Sarver 2004 {published data only}

Tamayo-Sarver JH, Baker DW. Comparison of responses to a US 2 dollar bill versus a chance to win 250 US dollars in a mail survey of emergency physicians. Academic Emergency Medicine 2004;11(8):888-91.

Tambor 1993 {published and unpublished data}

Tambor ES, Chase GA, Faden RR, Geller G, Hofman KJ, Holtzman NA. Improving response rates through incentives and follow-up: the effect on a survey of physician's knowledge of genetics. American Journal of Public Health 1993;83:1599-603.

Tariq 2021 {published data only}

Tariq M B, Jones M H, Strnad G, Sosic E, Spindler K P. A Last-Ditch Effort and Personalized Surgeon Letter Improves PROMs Follow-Up Rate in Sports Medicine Patients: A Crossover Randomized Controlled Trial. JOURNAL OF KNEE SURGERY 2021;34(02):130-6.

Taylor 1998 {published data only}

Taylor S, Lynn P. The effect of a preliminary notification letter on response to a postal survey of young people. The Journal of the Market Research Society 1998;40(2):165-73.

Taylor 2006 {published data only}

Taylor KS, Counsell CE, Harris CE, Gordon JC, Fonseca SC, Lee AJ. In a randomized study of envelope and ink color, colored ink was found to increase the response rate to a postal questionnaire. Journal of Clinical Epidemiology 2006;59(12):1326-30.

Taylor 2019 {published data only}

Taylor Sara, Ferguson Craig, Peng Fengjiao, Schoeneich Magdalena, Picard Rosalind W. Use of In-Game Rewards to Motivate Daily Self-Report. JOURNAL OF MEDICAL INTERNET RESEARCH 2019;21(1):e11683.

Teisl 2005 {published data only}

Teisl MF, Roe B, Vayda M. Incentive effects on response rates, data quality, and survey administration costs. International Journal of Public Opinion Research 2005;18(3):364-73.

Temple‐Smith 1998 {published data only}

Temple-Smith M, Mulvey G, Doyle W. Maximising response rates in a survey of general practitioners - lessons from a Victorian survey on sexually transmissible diseases. Australian Family Physician 1998;27(Suppl 1):S15-8.

Thistlethwaite 1993 {published data only}

Thistlethwaite PC. The impact of selected mail response enhancement techniques on surveys of the mature market: some new evidence. Journal of Professional Services Marketing 1993;8(2):269-76.

Thomson 2004 {published data only}

Thomson CE, Paterson-Brown S, Russell D, McCaldin D, Russell IT. Short report: encouraging GPs to complete postal questionnaires - one big prize or many small prizes? A randomized controlled trial. Family Practice 2004;21(6):697-8.

Tilbrook 2014 {published data only}

Tilbrook HE, Becque T, Buckley H, MacPherson H, Bailey M, Torgerson DJ. Randomized trial within a trial of yellow 'post-it notes' did not improve questionnaire response rates among participants in a trial of treatments for neck pain. J Eval Clin Pract 2014;21(2):202‐204.

Tjerbo 2005 {published data only}

Tjerbo T, Kvaemer KJ, Botten G, Aasland OG. Bruk av incentiver for a oke svarandelen i sporreskjemaundersokelser. Tidsskr Nor Laegeforen 2005;18(125):2496-7.

Todd 2015 {published data only}

Todd A L, Porter M, Williamson J L, Patterson J A, Roberts C L. Pre-notification letter type and response rate to a postal survey among women who have recently given birth. BMC MEDICAL RESEARCH METHODOLOGY 2015;15:104.

Trussell 2004a {published data only}

Trussell N, Lavrakas PJ. The influence of incremental increases in token cash incentives on mail survey response. Public Opinion Quarterly 2004a;68(3):349-67.

Trussell 2004b {published data only}

Trussell N, Lavrakas PJ. The influence of incremental increases in token cash incentives on mail survey response. Public Opinion Quarterly 2004b;68(3):349-67.

Trussell 2004c {published data only}

Trussell N, Lavrakas PJ. The influence of incremental increases in token cash incentives on mail survey response. Public Opinion Quarterly 2004c;68(3):349-67.

Tullar 1979 {published data only}

Tullar WL, Pressley MM, Gentry DL. Toward a theoretical framework for mail survey response. Proceeding of the Third Annual Conference of the Academy of Marketing Science 1979;2:243-7.

Tullar 2004 {published data only}

Tullar JM, Katz JN, Wright EA, Fossel AH, Phillips CB, Maher NE, et al. Effect of handwritten, hand-stamped envelopes on response rate in a follow up study of hip replacement patients. Arthritis & Rheumatism 2004;51(3):501-4.

Turnbull 2015 {published data only}

Turnbull A E, O'Connor C L, Lau B, Halpern S D, Needham D M. Allowing Physicians to Choose the Value of Compensation for Participation in a Web-Based Survey: Randomized Controlled Trial. JOURNAL OF MEDICAL INTERNET RESEARCH 2015;17(7):e189.

Tuten 2004 {published data only}

Tuten TL, Galesic M, Bosnjak M. Effects of immediate versus delayed notification of prize draw results on response behavior in web surveys: an experiment. Social Science Computer Review 2004;22:377-84.

Ulrich 2005 {published data only}

Ulrich CM, Danis M, Koziol D, Garrett-Mayer E, Hubbard R, Grady C. Does it pay to pay? A randomized trial of prepaid financial incentives and lottery incentives in surveys of nonphysician healthcare professionals. Nursing Research 2005;54(3):178-83.

Urban 1993 {published data only}

Urban N, Anderson GL, Tseng A. Effects on response rates and costs of stamps vs business reply in a mail survey of physicians. Clinical Epidemiology 1993;46(5):455-9.

van den Berg 2011 {published data only}

Van den Berg MH, Overbeek A, Van der Pal HJ, Versluys AB, Bresters D, Van Leeuwen FE, et al. Using Web-Based and Paper-Based Questionnaires for Collecting Data on Fertility Issues Among Female Childhood Cancer Survivors: Differences in Response Characteristics. JOURNAL OF MEDICAL INTERNET RESEARCH 2011;13(3):e76.

van der Mark 2012 {published data only}

Van der Mark Lonneke B, Van Wonderen Karina E, Mohrs Jacob, Bindels Patrick Je, Puhan Milo A, Ter Riet Gerben. The effect of two lottery-style incentives on response rates to postal questionnaires in a prospective cohort study in preschool children at high risk of asthma: a randomized trial. BMC Medical Research Methodology 2012;12(100968545):186.

VanGeest 2001 {published data only}

VanGeest JB, Wynia MK, Cummins DS, Wilson IB. Effects of different monetary incentives on the return rate of a national mail survey of physicians. Medical Care 2001;39(2):197-201.

Van Mol 2017 {published data only}

Van Mol Christof. Improving web survey efficiency: the impact of an extra reminder and reminder content on web survey response. INTERNATIONAL JOURNAL OF SOCIAL RESEARCH METHODOLOGY 2017;20(4):317-27.

Veen 2015 {published data only}

Veen Floris van, Göritz Anja S, Sattler Sebastian. Response Effects of Prenotification, Prepaid Cash, Prepaid Vouchers, and Postpaid Vouchers: An Experimental Comparison. SOCIAL SCIENCE COMPUTER REVIEW 2015;34(3):333-46.

Veiga 1974 {published data only}

Veiga JF. Getting the mail questionnaire returned: Some practical research considerations. Journal of Applied Psychology 1974;59(2):217-8.

Viera 2012 {published data only}

Viera Anthony J, Edwards Teresa. Does an offer for a free on-line continuing medical education (CME) activity increase physician survey response rate? A randomized trial. BMC research notes 2012;5(101462768):129.

Virtanen 2007a {published data only}

Virtanen V, Sirkiä T, Jokiranta V. Reducing nonresponse by SMS reminders in mail surveys. Social Science Computer Review 2007a;25:384-95.

Virtanen 2007b {published data only}

Virtanen V, Sirkiä T, Jokiranta V. Reducing nonresponse by SMS reminders in mail surveys. Social Science Computer Review 2007b;25:384-95.

Virtanen 2007c {published data only}

Virtanen V, Sirkiä T, Jokiranta V. Reducing nonresponse by SMS reminders in mail surveys. Social Science Computer Review 2007c;25:384-95.

Vocino 1977 {published data only}

Vocino T. Three variables in stimulating responses to mailed questionnaires. Journal of Marketing 1977;41:76-7.

Vogel 1992 {published data only}

Vogel PA, Skjostad K, Eriksen L. Influencing return rate by mail of alcoholics' questionnaires at follow-up by varying lottery procedures and questionnaire lengths. Two experimental studies. European Journal of Psychiatry 1992;6(4):213-22.

VonRiesen 1979 {published data only}

VonRiesen RD. Postcard reminders versus replacement questionnaires and mail survey response rates from a professional population. Journal of Business Research 1979;7:1-7.

Waisanen 1954 {published data only}

Waisanen FB. A note on the response to a mailed questionnaire. Public Opinion Quarterly 1954;18:210-2.

Wakabayashi 2012 {published data only}

Wakabayashi C, Hayashi K, Nagai K, Sakamoto N, Iwasaki Y. Effect of stamped reply envelopes and timing of newsletter delivery on response rates of mail survey: a randomised controlled trial in a prospective cohort study. BMJ OPEN 2012;2(5):e001181.

Walker 1997 {unpublished data only}

Walker N on behalf of the Auckland Leg Ulcer Study Group. unpublished data only. Auckland Leg Ulcer Study - Trial data 1997-8.

Waltemyer 2005 {published data only}

Waltemyer S, Sagas M, Cunningham GB, Jordan JS, Turner BA. The effects of personalization and colored paper on mailed questionnaire response rates in a coaching sample. Research Quarterly for Exercise and Sport 2005;76(1):A130.

Wan 2012 {published data only}

Wan J, Abuabara K, Shin DB, Troxel AB, Bebo BF Jr, Gelfand JM. Dermatologist response rates to a mailed questionnaire: a randomized trial of monetary incentives. J Am Acad Dermatol 2012;66(1):e18-20.

Ward 1996 {published data only}

Ward J, Boyle C, Long D, Ovadia C. Patient surveys in general practice. Australian Family Physician 1996;25(1):S19-S20.

Ward 1998 {published data only}

Ward J, Bruce T, Holt P, D'Este K, Sladden M. Labour-saving strategies to maintain survey response rates: a randomised trial. Australian and New Zealand Journal of Public Health 1998;22(3 Suppl):394-6.

Warriner 1996 {published and unpublished data}

Warriner K, Goyder J, Gjertsen H, Hohner P, McSpurren K. Charities, no; lotteries, no; cash, yes. Public Opinion Quarterly 1996;60:542-62.

Warwick 2019 {published data only}

Warwick H, Hutyra C, Politzer C, Francis A, Risoli T, Green C, et al. Small Social Incentives Did Not Improve the Survey Response Rate of Patients Who Underwent Orthopaedic Surgery: A Randomized Trial. CLINICAL ORTHOPAEDICS AND RELATED RESEARCH 2019;477(7):1648-56.

Weaver 2019 {published data only}

Weaver Lesley, Beebe Timothy J, Rockwood Todd. The impact of survey mode on the response rate in a survey of the factors that influence Minnesota physicians' disclosure practices. BMC medical research methodology 2019;19(1):73.

Webborn 2022 {published data only}

Webborn E, McKenna E, Elam S, Anderson B, Cooper A, Oreszczyn T. Increasing response rates and improving research design: Learnings from the Smart Energy Research Lab in the United Kingdom. ENERGY RESEARCH & SOCIAL SCIENCE 2022;83:102312.

Weilbacher 1952 {published data only}

Weilbacher WM, Walsh HR. Mail questionnaires and the personalized letter of transmittal. Marketing Notes 1952;16:331-6.

Weir 1999 {unpublished data only}

Weir N. Methods of following up stroke patients. Neurosciences Trials Unit, University of Edinburgh.

Wells 1984 {unpublished data only}

Wells DV. The representativeness of mail questionnaires as a function or sponsorship, return postage, and time of response. Doctoral Dissertation 1984.

Weltzien 1986 {published data only}

Weltzien RT, McIntyre TJ, Ernst JA, Walsh JA, Parker JK. Crossvalidation of some psychometric properties of the CSQ and its differential return rate as a function of token financial incentives. Community Mental Health Journal 1986;22(1):49-55.

Wenemark 2010 {published data only}

Wenemark M, Vernby A, Norberg A L. Can incentives undermine intrinsic motivation to participate in epidemiologic surveys? EUROPEAN JOURNAL OF EPIDEMIOLOGY 2010;25(4):231-5.

Wensing 1999a {published data only}

Wensing M, Mainz J, Kramme O, Jung HP, Ribacke M. Effect of mailed reminders on the response rate in surveys among patients in general practice. Journal of Clinical Epidemiology 1999;52(6):585-7.

Wensing 1999b {published data only}

Wensing M, Mainz J, Kramme O, Jung HP, Ribacke M. Effect of mailed reminders on the response rate in surveys among patients in general practice. Journal of Clinical Epidemiology 1999;52(6):585-7.

Wensing 2005 {published data only}

Wensing M, Schattenberg G. Initial nonresponders had an increased response rate after repeated questionnaire mailings. Journal of Clinical Epidemiology 2005;58:959–61.

Whitcomb 2004 {published data only}

Whitcomb ME, Porter SR. E-mail contacts: a test of complex graphical designs in survey research. Social Science Computer Review 2004;22:370-6.

White 1997 {published data only}

White MB, Chambers KM. Type of cover letter and questionnaire color: do they influence the response rate in survey research with marriage and family therapists? Family Therapy 1997;24(1):19-24.

White 2005a {published data only}

White E, Carney PA, Kolar AS. Increasing response to mailed questionnaires by including a pencil/pen. American Journal of Epidemiology 2005a;162(3):261-6.

White 2005b {published data only}

White E, Carney PA, Kolar AS. Increasing response to mailed questionnaires by including a pencil/pen. American Journal of Epidemiology 2005b;162(3):261-5.

Whitehead 2011 {published data only}

Whitehead Lisa. Methodological issues in Internet-mediated research: a randomized comparison of internet versus mailed questionnaires. Journal of medical Internet research 2011;13(4):e109.

Whiteman 2003 {published data only}

Whiteman MK, Langenberg P, Kjerulff K, McCarter R, Flaws JA. A randomized trial of incentives to improve response rates to a mailed women's health questionnaire. Journal of Women's Health 2003;12(8):821-8.

Whiteside 2019 {published data only}

Whiteside Katie, Flett Lydia, Mitchell Alex, Fairhurst Caroline, Cockayne Sarah, Rodgers Sara, et al. Using pens as an incentive for trial recruitment of older adults: An embedded randomised controlled trial. F1000Research 2019;8(101594320):315.

Whitmore 1976 {published data only}

Whitmore WJ. Mail survey premiums and response bias. Journal of Marketing Research 1976;13:46-50.

Wiant 2018 {published data only}

Wiant Kristine, Geisen Emily, Creel Darryl, Willis Gordon, Freedman Andrew, de Moor Janet, et al. Risks and rewards of using prepaid vs. postpaid incentive checks on a survey of physicians. BMC medical research methodology 2018;18(1):104.

Willits 1995 {published data only}

Willits FK, Ke B. Part-whole question order effects. Public Opinion Quarterly 1995;59:392-403.

Wilson 2010 {published data only}

Wilson P M, Petticrew M, Calnan M, Nazareth I. Effects of a Financial Incentive on Health Researchers' Response to an Online Survey: a Randomized Controlled Trial. JOURNAL OF MEDICAL INTERNET RESEARCH 2010;12(2):e13.

Windsor 1992 {published data only}

Windsor J. What can you ask about? The effect on response to a postal screen of asking about two potentially sensitive questions. Journal of Epidemiology and Community Health 1992;46:83-5.

Wiseman 1972 {published data only}

Wiseman F. Methodological bias in public opinion surveys. Public Opinion Quarterly 1972;36:105-8.

Wiseman 1973 {published data only}

Wiseman F. Factor interaction effects in mail survey response rates. Journal of Marketing Research 1973;10:330-3.

Wong 2021 {published data only}

Wong HZ, Brusseleers M, Hall KA, Maiden MJ, Chapple LS, Chapman MJ, Hodgson CL, Gluck S. Mixed-mode versus paper surveys for patient-reported outcomes after critical illness: A randomised controlled trial. Australian Critical Care 2021;35(3):286-293.

Woodward 1985 {published data only}

Woodward A, Douglas B, Miles H. Chance of a free dinner increases response to mail questionnaire. International Journal of Epidemiology 1985;14:641-2.

Woolf 2021 {published data only}

Woolf B, Edwards P. Does pre-notification increase questionnaire response rates: a randomised controlled trial nested within a systematic review. BMC MEDICAL RESEARCH METHODOLOGY 2021;21(259):1-7. [DOI: ]

Worthen 1985a {published data only}

Worthen BR, Valcarce RW. Relative effectiveness of personalized and form covering letters in initial and follow-up mail surveys. Psychology Reports 1985;57:735-44.

Worthen 1985b {published data only}

Worthen BR, Valcarce RW. Relative effectiveness of personalized and form covering letters in initial and follow-up mail surveys. Psychology Reports 1985;57:735-44.

Worthen 1985c {published data only}

Worthen BR, Valcarce RW. Relative effectiveness of personalized and form covering letters in initial and follow-up mail surveys. Psychology Reports 1985;57:735-44.

Wotruba 1966 {published data only}

Wotruba TR. Monetary inducements and mail questionnaire response. Journal of Marketing Research 1966;3:398-400.

Wright 1984 {unpublished data only}

Wright SJ. Mail survey response rates: a test of four techniques designed to increase response rates and a discussion of the associated cost considerations. Student Research Report, Department of Marketing, Massey University 1984.

Wright 1995 {published data only}

Wright M. The effect of pre-notification on mail survey response rates: an experimental result. Marketing Bulletin 1995;6:59-64.

Wunder 1988 {published data only}

Wunder GC, Wynn GW. The effects of address personalisation on mailed questionnaires response rate, time and quality. Journal of the Market Research Society 1988;30(1):95-101.

Wynn 1985 {published data only}

Wynn GW, McDaniel SW. The effect of alternative foot-in-the-door manipulations on mailed questionnaire response rate and quality. Journal of the Market Research Society 1985;27(1):15-26.

Xie 2013 {published data only}

Xie Y J, Ho S C. Prenotification had no additional effect on the response rate and survey quality: a randomized trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2013;66(12):1422-6.

Yetter 2010 {published data only}

Yetter Georgette, Capaccioli Kristen. Differences in responses to Web and paper surveys among school professionals. Behavior research methods 2010;42(1):266-72.

Young 2015 {published data only}

Young J M, O'Halloran A, McAulay C, Pirotta M, Forsdike K, Stacey I, et al. Unconditional and conditional incentives differentially improved general practitioners' participation in an online survey: randomized controlled trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2015;68(6):693-7.

Young 2020 {published data only}

Young Ben, Bedford Laura, das Nair Roshan, Gallant Stephanie, Littleford Roberta, Robertson John F R, et al. Unconditional and conditional monetary incentives to increase response to mailed questionnaires: A randomized controlled study within a trial (SWAT). Journal of evaluation in clinical practice 2020;26(3):893-902.

Yu 2017 {published data only}

Yu S C, Alper H E, Nguyen A M, Brackbill R M, Turner L, Walker D J, et al. The effectiveness of a monetary incentive offer on survey response rates and response completeness in a longitudinal study. BMC MEDICAL RESEARCH METHODOLOGY 2017;17(1):77.

Ziegenfuss 2010 {published data only}

Ziegenfuss Jeanette Y, Beebe Timothy J, Rey Enrique, Schleck Cathy, Locke G Richard III, Talley Nicholas J. Internet Option in a Mail Survey: More Harm Than Good? Epidemiology 2010;21(4):585-586.

Ziegenfuss 2011 {published data only}

Ziegenfuss Jeanette Y, Shah Nilay D, Deming James R, Van Houten Holly K, Smith Steven A, Beebe Timothy J. Offering results to participants in a diabetes survey: effects on survey response rates. The patient 2011;4(4):241-5.

Ziegenfuss 2012 {published data only}

Ziegenfuss J Y, Burmeister K, James K M, Haas L, Tilburt J C, Beebe T J. Getting physicians to open the survey: little evidence that an envelope teaser increases response rates. BMC MEDICAL RESEARCH METHODOLOGY 2012;12:41.

Ziegenfuss 2014 {published data only}

Ziegenfuss J Y, Tilburt J C, Lackore K, Jenkins S, James K, Beebe T J. Envelope Type and Response Rates in a Survey of Health Professionals. FIELD METHODS 2014;26(4):380-9.

Zusman 1987 {published data only}

Zusman BJ, Duby P. An evaluation of the use of monetary incentives in postsecondary survey research. Journal of Research and Development in Education 1987;20(4):73-8.

References to studies excluded from this review

Alcaraz 2020 {published data only}

Alcaraz Kassandra I, Vereen Rhyan N, Burnham Donna. Use of Telephone and Digital Channels to Engage Socioeconomically Disadvantaged Adults in Health Disparities Research Within a Social Service Setting: Cross-Sectional Study.. Journal of Medical Internet Research 2020;22(4):N.PAG-N.PAG-N.PAG-N.PAG. [DOI: 10.2196/16680]

Alexander 2008a {published data only}

Alexander Gwen L, Divine George W, Couper Mick P, McClure Jennifer B, Stopponi Melanie A, Fortman Kristine K, Tolsma Dennis D, Strecher Victor J, Johnson Christine Cole. Effect of incentives and mailing features on online health program enrollment.. American journal of preventive medicine 2008;34(5):382-8-382-8. [DOI: ]

Allen 1980 {published data only}

Allen CT. More on self-perception theory’s foot technique in the pre-call/mail survey setting. Journal of Marketing Research 1980;17:498-502.

Anderson 1975 {published data only}

Anderson JF. Effects of response rates of formal and informal questionnaire follow-up techniques. Journal of Applied Psychology 1975;60(2):255-7.

Anderson 2007 {published data only}

Anderson DA, Simmons AM, Milnes SM, Earleywine M. Effect of response format on endorsement of eating disordered attitudes and behaviors.. International Journal of Eating Disorders 2007;40(1):90-93-90-93. [DOI: 10.1002/eat.20342]

Angus 2003 {published data only}

Angus VC, Entwistle VA, Emslie MJ, Walker KA, Andrew JE. The requirement for prior consent to participate on survey response rates: a population-based survey in Grampian. BMC Health Services Research 2003;3(21):1-10.

Antoun 2020 {published data only}

Antoun C, Cernat A. Factors Affecting Completion Times: A Comparative Analysis of Smartphone and PC Web Surveys. SOCIAL SCIENCE COMPUTER REVIEW 2020;38(4):477-489-477-489. [DOI: 10.1177/0894439318823703]

Armstrong 1975 {published data only}

Armstrong JS. Monetary incentives in mail surveys. Public Opinion Quarterly 1975;39:111-6.

Asch 1994 {published data only}

Asch DA, Christakis NA. Different response rates in a trial of two envelope styles in mail survey research. Epidemiology 1994;5(3):364-5.

Ash 1952 {published data only}

Ash P. The effect of anonymity on attitude-questionnaire response. Journal of Abnormal and Social Psychology 1952;47:722-3.

Baron 2001 {published data only}

Baron G, De Wals P, Milord F. Cost-effectiveness of a lottery for increasing physicians' responses to a mail survey. Evaluation and the Health Professions 2001;24(1):47-52.

Beaty 2018 {published data only}

Beaty Brenda L, Brtnikova Michaela, Allison Mandy A, Kempe Allison, Crane Lori A, Hurley Laura P. A method for achieving high response rates in national surveys of U.S. primary care physicians. PLoS ONE 2018;13(8):e0202755-e0202755-. [DOI: ]

Becker 2019 {published data only}

Becker Rolf, Moser Sara, Glauser David. Cash vs. vouchers vs. gifts in web surveys of a mature panel study--Main effects in a long-term incentives experiment across three panel waves. Social science research 2019;81((Becker, Moser, Glauser) University of Bern Department of Sociology of Education, Fabrikstrasse 8, Bern CH-3012, Switzerland):221-234-221-234. [DOI: ]

Beebe 2011 {published data only}

Beebe Timothy J, Ziegenfuss Jeanette Y, St Sauver Jennifer L, Jenkins Sarah M, Haas Lindsey, Davern Michael E, Talley Nicholas J. Health Insurance Portability and Accountability Act (HIPAA) authorization and survey nonresponse bias.. Medical care 2011;49(4):365-70-365-70. [DOI: ]

Berthelot 1993 {published data only}

Berthelot Jean-Marie, Latouche Michel. Improving the Efficiency of Data Collection: A Generic Respondent Follow-Up Strategy for Economic Surveys. Journal of Business and Economic Statistics 1993;11(4):417-24-417-24.

Bevis 1948 {published data only}

Bevis JC. Economical incentive used for mail questionnaire. Public Opinion Quarterly 1948;12:492-3.

Beynon 2010 {published data only}

Beynon Caryl M, Taylor Avril, Allen Elizabeth, Bellis Mark A. Visual versus written cues: a comparison of drug injectors' responses. Have surveys using the written word underestimated risk behaviors for hepatitis C? Substance use & misuse 2010;45(10):1491-1508-1491-1508. [DOI: ]

Biggar 1992 {published data only}

Biggar RJ, Melbye M. Responses to anonymous questionnaires concerning sexual behaviour: a method to examine potential biases. American Journal of Public Health 1992;82(11):1506-12.

Blumberg 1974 {published data only}

Blumberg H, Fuller C, Hare AP. Response rates in postal surveys. Public Opinion Quarterly 1974;38:113-23.

Blumenfeld 1973 {published data only}

Blumenfeld WS. Effect of appearance of correspondence on response rate to a mail questionnaire survey. Psychological Reports 1973;32:178.

Boucher 2015 {published data only}

Boucher S, Gray A, Leong SL, Sharples H, Horwath C. Token monetary incentives improve mail survey response rates and participant retention: results from a large randomised prospective study of mid-age New Zealand women. NEW ZEALAND MEDICAL JOURNAL 2015;128(1413):20-30-20-30.

Brealey 2007 {published data only}

Brealey SD, Atwell C, Bryan S, Coulton S, Cox H, Cross B, Fylan F, Garratt A, Gilbert FJ, Gillan MGC, Hendry M, Hood K, Houston H, King D, Morton V, Orchard J, Robling M, Russell IT, Torgerson D, Wadsworth V, Wilkinson C. Improving response rates using a monetary incentive for patient completion of questionnaires: an observational study. BMC MEDICAL RESEARCH METHODOLOGY 2007;7:12. [DOI: 10.1186/1471-2288-7-12]

Brechner 1976 {published data only}

Brechner K, Shippee G, Obitz FW. Compliance techniques to increase mailed questionnaire return rates from alcoholics. Journal of Studies on Alcohol 1976;37(7):995-6.

Breeman 2013 {published data only}

Breeman Suzanne, Cotton Seonaidh, McDonald Alison, McPherson Gladys, MacLennan Graeme, Bruhn Hanne. Telephone calls to boost response rates in the collection of outcome data. Trials 2013;14(SUPPL. 1):207DUMMY-207DUMMY-.

Brennan 1958 {published data only}

Brennan RD. Trading stamps as an incentive in mail surveys. Journal of Marketing 1958;22(3):306-7.

Brennan 1990 {published data only}

Brennan M, Hoek J, Astridge C. The effects of monetary incentives on the response rate and cost-effectiveness of a mail survey. Journal of the Market Research Society 1990;33:229-41.

Burkhart 2021 {published data only}

Burkhart Q, Orr Nate, Brown Julie A, Hays Ron D, Cleary Paul D, Beckett Megan K, Perry Suzanne E, Gaillot Sarah, Elliott Marc N. Associations of Mail Survey Length and Layout With Response Rates.. Medical Care Research & Review 2021;78(4):441-448-441-448. [DOI: 10.1177/1077558719888407]

Cadilhac 2012 {published data only}

Cadilhac DA, Lannin N, Lim J, Anderson C, Price C, Faux S, Levi C, Donnan GA. Randomised comparative efficiency of telephone versus mail follow-up in the Australian Stroke Clinical Registry (AuSCR). Cerebrovascular Diseases 2012;33(SUPPL. 2):21-21-. [DOI: ]

Callegaro 2010 {published data only}

Callegaro Mario, McCutcheon Allan L, Ludwig Jack. Who's calling? The impact of caller ID on telephone survey response.. Field Methods 2010;22(2):175-191-175-191. [DOI: ]

Cartwright 1968 {published data only}

Cartwright A, Ward AWM. Variations in general practitioners' response to postal questionnaires. British Journal of Preventive and Social Medicine 1968;22:199-205.

Cartwright 1989 {published data only}

Cartwright A, Windsor J. Some further experiments with factors that might affect the response to postal questionnaires. Survey of Methodology Bulletin 1989;25:11-5.

Cernat 2018 {published data only}

Cernat Alexandru, Lynn Peter. The role of e-mail communications in determining response rates and mode of participation in a mixed-mode design.. Field Methods 2018;30(1):70-87-70-87. [DOI: ]

Champion 1969 {published data only}

Champion DJ, Sear AM. Questionnaire response rate: a methodological analysis. Social Forces 1969;47(3):335-9.

Chen 2016 {published data only}

Chen Jane S, Sprague Brian L, Klabunde Carrie N, Tosteson Anna NA, Bitton Asaf, Onega Tracy, MacLean Charles D, Harris Kimberly, Schapira Marilyn M, Haas Jennifer S. Take the money and run? Redemption of a gift card incentive in a clinician survey.. BMC Medical Research Methodology 2016;16:1-5-1-5. [DOI: 10.1186/s12874-016-0126-2]

Cheung 2019 {published data only}

Cheung Yee Tak Derek, Weng Xue, Wang Man Ping, Ho Sai Yin, Kwong Antonio Cho Shing, Lai Vienna Wai Yin, Lam Tai Hing. Effect of prepaid and promised financial incentive on follow-up survey response in cigarette smokers: a randomized controlled trial.. BMC medical research methodology 2019;19(1):138-138-. [DOI: ]

Childs 2005 {published data only}

Childs LA, The Submacular Surgery Trials Research Group. Effect of order of administration of health-related quality of life interview instruments on responses. Quality of Life Research 2005;14:493–500.

Chin 2015 {published data only}

Chin WY, Choi EPH, Lam CLK. The effect of timing of incentive payments on response rates for cohort study telephone interviews in primary care setting with cost-minimization analysis, a randomized controlled trial. BMC MEDICAL RESEARCH METHODOLOGY 2015;15:79. [DOI: 10.1186/s12874-015-0073-3]

Choi 2017 {published data only}

Seung Hee Choi, Mitchell Jason, Lipkus Isaac. Lessons Learned From an Online Study with Dual-smoker Couples.. American Journal of Health Behavior 2017;41(1):61-66-61-66. [DOI: 10.5993/AJHB.41.1.6]

Chyou 2017 {published data only}

Chyou PH, Schroeder D, Schwei K, Acharya A. Statistical Application and Cost Saving in a Dental Survey. CLINICAL MEDICINE & RESEARCH 2017;15(1-2):1-5-1-5. [DOI: 10.3121/cmr.2017.1323]

Clark 2008 {published data only}

Clark Melissa A, Rogers Michelle L, Armstrong Gene F, Rakowski William, Kviz Frederick J. Differential response effects of data collection mode in a cancer screening study of unmarried women ages 40-75 years: a randomized trial.. BMC medical research methodology 2008;8(100968545):10-10-. [DOI: ]

Coleman 2021 {published data only}

Coleman Elizabeth, Whitemore Rachel, Clark Laura, Daykin Karen, Clark Miranda. Pre-notification and personalisation of text messages to increase questionnaire completion in a smoking cessation pregnancy RCT: an embedded randomised factorial trial.. F1000Research 2021;10(101594320):637-637-. [DOI: ]

Coleman 2021a {published data only}

Coleman Elizabeth, Whitemore Rachel, Clark Laura, Daykin Karen, Clark Miranda. Pre-notification and personalisation of text-messages to retain participants in a smoking cessation pregnancy RCT: an embedded randomised factorial trial.. F1000Research 2021;10(101594320):637-637-. [DOI: ]

Conrad 2007 {published data only}

Conrad Frederick G, Schober Michael F, Coiner Tania. Bringing features of human dialogue to web surveys. Applied Cognitive Psychology 2007;21(2):165-187-165-187. [DOI: ]

Cook 1985 {published data only}

Cook JR, Schoeps N, Kim S. Program responses to mail surveys as a function of monetary incentives. Psychological Reports 1985;57:366.

Dal Grande 2016 {published data only}

Dal Grande Eleonora, Chittleborough Catherine Ruth, Campostrini Stefano, Dollard Maureen, Taylor Anne Winifred. Pre-Survey Text Messages (SMS) Improve Participation Rate in an Australian Mobile Telephone Survey: An Experimental Study.. PloS one 2016;11(2):e0150231-e0150231-. [DOI: ]

Desborough 2008 {published data only}

Desborough JA, Butters P, Bhattacharya D, Holland RC, Wright DJ. Does it matter whether the recipient of patient questionnaires in general practice is the general practitioner or an independent researcher? The REPLY randomised trial. BMC MEDICAL RESEARCH METHODOLOGY 2008;8:42. [DOI: 10.1186/1471-2288-8-42]

Dillman 1972 {published data only}

Dillman DA. Increasing mail questionnaire response in large samples of the general public. Public Opinion Quarterly 1972;36:254-7.

Down 2010 {published data only}

Down Liz, Wade Julia, Neal David, Hamdy Freddie, Donovan Jenny, Lane JAthene. Factors influencing questionnaire response rates in trials. Clinical Trials 2010;7(4):460-460-. [DOI: ]

Drake 2014 {published data only}

Drake Keith M, Hargraves J Lee, Lloyd Stephanie, Gallagher Patricia M, Cleary Paul D. The effect of response scale, administration mode, and format on responses to the CAHPS Clinician and Group survey.. Health services research 2014;49(4):1387-99-1387-99. [DOI: ]

Drummond 2015 {published data only}

Drummond F J, O'Leary E, Sharp L. Lottery ticket was more effective than a prize draw in increasing questionnaire response among cancer survivors. JOURNAL OF CLINICAL EPIDEMIOLOGY 2015;68(7):769-75.

Duan 2007 {published data only}

Duan Naihua, Alegria Margarita, Canino Glorisa, McGuire Thomas G, Takeuchi David. Survey conditioning in self-reported mental health service use: Randomized comparison of alternative instrument formats: Methods articles. Health Services Research 2007;42(2):890-907-890-907. [DOI: ]

Duncan 2019 {published data only}

Duncan Anne, Treweek Shaun, Goodman Kirsteen, Hagan Suzanne. Same intervention, different opinions: Some challenges of doing Study Within A Trial (SWAT) replication studies. Trials 2019;20(Supplement 1):PS1A. [DOI: ]

Dunlap 1950 {published data only}

Dunlap JW. The effect of colour in direct mail advertising. Journal of Applied Psychology 1950;34:280-1.

Eaton 2020 {published data only}

Eaton Cyd, Comer Margaret, Pruette Cozumel, Psoter Kevin, Riekert Kristin. Text Messaging Adherence Intervention for Adolescents and Young Adults with Chronic Kidney Disease: Pilot Randomized Controlled Trial and Stakeholder Interviews.. Journal of medical Internet research 2020;22(8):e19861-e19861-. [DOI: ]

Ebert 2018 {published data only}

Ebert Jonas Fynboe, Huibers Linda, Christensen Bo, Christensen Morten Bondo. Paper- or Web-Based Questionnaire Invitations as a Method for Data Collection: Cross-Sectional Comparative Study of Differences in Response Rate, Completeness of Data, and Financial Cost.. Journal of medical Internet research 2018;20(1):e24-e24-. [DOI: ]

Egeland 2017 {published data only}

Egeland Merete T, Tarangen Magnus, Shiryaeva Olga, Gay Caryl, Dosen Liv K, Haye Rolf. Evaluation of strategies for increasing response rates to postal questionnaires in quality control of nasal septal surgery. BMC research notes 2017;10(1):189-189-. [DOI: ]

Eisinger 1974 {published data only}

Eisinger RA, Janicki WP, Stevenson RL, Thompson WL. Increasing returns in international mail surveys. Public Opinion Quarterly 1974;38:126-30.

Elinson 1950 {published data only}

Elinson J, Haines VT. Role of anonymity in attitude surveys. American Psychologist 1950;5:315.

Ettridge 2021 {published data only}

Ettridge Kerry, Caruso Joanna, Roder David, Prichard Ivanka, Scharling-Gamba Katrine, Wright Kathleen, Miller Caroline. A randomised online experimental study to compare responses to brief and extended surveys of health-related quality of life and psychosocial outcomes among women with breast cancer.. Quality of Life Research 2021;30(2):407-423-407-423. [DOI: 10.1007/s11136-020-02651-x]

Everett 1997 {published data only}

Everett SA, Price JH, Bedell A, Telljohann SK. The effect of a monetary incentive in increasing the return rate of a survey to family physicians. Evaluation & the Health Professions 1997;20(2):207-14.

Fang 2006 {published data only}

Fang J, Shao P. Does material incentive really improve the response rate in web-based survey? A classification model of the potential respondents. International Conference on Management Science & Engineering (13th) 2006;1-3:74-7.

Fang 2012 {published data only}

Fang Jiaming, Wen Chao, Pavur Robert. Participation Willingness in Web Surveys: Exploring Effect of Sponsoring Corporation's and Survey Provider's Reputation. Cyberpsychology, Behavior, and Social Networking 2012;15(4):195-199-195-199. [DOI: 10.1089/cyber.2011.0411]

Fang 2021 {published data only}

Fang Heping, Xian Ruoling, Ma Zhuoying, Lu Mingyue, Hu Yan. Comparison of the differences between web-based and traditional questionnaire surveys in pediatrics: Comparative survey study. Journal of Medical Internet Research 2021;23(8):e30861-e30861-. [DOI: ]

Fernandez Lynch 2019 {published data only}

Fernandez Lynch Holly, Joffe Steven, Thirumurthy Harsha, Xie Dawei, Largent Emily A. Association Between Financial Incentives and Participant Deception About Study Eligibility.. JAMA network open 2019;2(1):e187355-e187355-. [DOI: ]

Ferriss 1951 {published data only}

Ferriss AL. A note on stimulating response to questionnaires. American Sociological Review 1951;16:247-9.

Fleming 2013 {published data only}

Fleming Charles B, Marchesini Gina, Elgin Jenna, Haggerty Kevin P, Woodward Danielle, Abbott Robert D, Catalano Richard F. Use of Web and Phone Survey Modes to Gather Data From Adults About Their Young Adult Children: An Evaluation Based on a Randomized Design.. Field methods 2013;25(4):388-404-388-404.

Fu 2013 {published data only}

Fu M, Martínez-Sánchez JM, Sureda X, Martínez C, Ballbè M, Baranda L, Riccobene A, Fernández E. Handwritten versus scanned signature on the invitation letter: does it make any difference in participation in a population-based study? Eur J Epidemiol. 2013;28(11):931-4. [DOI: 10.1007/s10654-013-9838-3]

Furse 1981 {published data only}

Furse DH, Stewart DW, Rados DL. Effects of foot-in-the-door, cash incentives, and follow-ups on survey response. Journal of Marketing Research 1981;18:473-8.

Gerace 1995 {published data only}

Gerace TA, George VA, Arango IG. Response rates to six recruitment mailing formats and two messages about a nutrition program for women 50-79 years old. Controlled Clinical Trials 1995;16:422-31.

Gibson 2020 {published data only}

Gibson Anthony M, Bowling Nathan A. The effects of questionnaire length and behavioral consequences on careless responding.. European Journal of Psychological Assessment 2020;36(2):410-420-410-420. [DOI: ]

Gillespie 1975 {published data only}

Gillespie DF, Perry RW. Survey return rates and questionnaire appearance. Australian and New Zealand Journal of Sociology 1975;11(3):71-2.

Gooden 2021 {published data only}

Gooden Tiffany, Wright Alison, Swinn Eliza, Sizmur Steve. Optimising response rates in a national postal survey evaluating community mental health care: four interventions trialled. Journal of Mental Health 2021;32(1)((Gooden, Wright, Swinn, Sizmur) Picker Institute Europe, Oxford, United Kingdom):96-102. [DOI: ]

Groves 2011 {published data only}

Groves Robert M, Couper Mick P, Presser Stanley, Singer Eleanor, Tourangeau Roger, Acosta Giorgina Piani, Nelson Lindsay. "Experiments in producing nonresponse bias": Errata.. Public Opinion Quarterly 2011;75(4):819-819-.

Hansen 2004 {published data only}

Hansen J, Alessandril PT, Croft ML, Burton PR, Klerk NH. The Western Australian register of childhood multiples: effects of questionnaire design and follow-up protocol on response rates and representativeness. Twin Research 2004;7(2):149-61.

Hare 1998 {published data only}

Hare S, Price JH, Flynn MG, King KA. Increasing return rates of a mail survey to exercise professionals using a modest monetary incentive. Perceptual and Motor Skills 1998;86:217-8.

Harlow 1993 {published data only}

Harlow BL. Telephone answering machines: the influence of leaving messages on telephone interviewing response rates. Epidemiology 1993;4(4):380-3.

Harrison 2019 {published data only}

Harrison Siân, Henderson Jane, Alderdice Fiona, Quigley Maria A. Methods to increase response rates to a population-based maternity survey: a comparison of two pilot studies.. BMC Medical Research Methodology 2019;19(1):N.PAG-N.PAG-N.PAG-N.PAG. [DOI: 10.1186/s12874-019-0702-3]

Haugejorden 1987 {published and unpublished data}

Haugejorden O, Nielsen WA. Experimental study of two methods of data collection by questionnaire. Community Dentistry & Oral Epidemiology 1987;15:205-8.

Hawes 1987 {published data only}

Hawes JM, Crittenden VL, Crittenden WF. The effects of personalisation, source, and offer on mail survey response rate and speed. Akron Business and Economic Review 1987;18:54-63.

Heads 1966 {published data only}

Heads J, Thrift HJ. Notes on a study in postal response rates. Commentary 1966;8(4):257-62.

Heje 2006 {published data only}

Heje NH, Vedsted P, Olesen F. A cluster-randomized trial of the significance of a reminder procedure in a patient evaluation survey in general practice. International Journal for Quality in Health Care 2006;18(3):232–7.

Helgeson 2002 {published data only}

Helgeson JG, Voss KE, Terpening WD. Determinants of mail-survey response: survey design factors and respondent factors. Psychology & Marketing 2002;19(3):303-28.

Hennrich 2021 {published data only}

Hennrich P, Arnold C, Wensing M. Effects of personalized invitation letters on research participation among general practitioners: a randomized trial. BMC MEDICAL RESEARCH METHODOLOGY 2021;21(1):247. [DOI: 10.1186/s12874-021-01447-y]

Hing 2005 {published data only}

Hing E, Schappert SM, Burt CW, Shimizu IM. Effects of form length and item format on response patterns and estimates of physician office and hospital outpatient department visits. Vital Health Statistics 2005;2(139):1-32.

Hinrichs 1975 {published data only}

Hinrichs JR. Factors related to survey response rates: effects of sampling, follow up letters, and commitment to participation on mail attitude survey response. Journal of Applied Psychology 1975;60(2):249-51.

Hocking 2006 {published data only}

Hocking JS, Lim MSC, Read T, Hellard M. Postal surveys of physicians gave superior response rates over telephone interviews in a randomized trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2006;59(5):521-524-521-524. [DOI: 10.1016/j.jclinepi.2005.10.009]

Horevoorts 2015 {published data only}

Horevoorts Nicole Je, Vissers Pauline Aj, Mols Floortje, Thong Melissa Sy, de Poll-Franse Lonneke V. Response rates for patient-reported outcomes using web-based versus paper questionnaires: comparison of two invitational methods in older colorectal cancer patients.. Journal of medical Internet research 2015;17(5):e111-e111-. [DOI: ]

Hsu 2017 {published data only}

Hsu Joanne W, Schmeiser Maximilian D, Haggerty Catherine, Nelson Shannon. The effect of large monetary incentives on survey completion: Evidence from a randomized experiment with the Survey of Consumer Finances.. Public Opinion Quarterly 2017;81(3):736-747-736-747. [DOI: ]

Hughes 1989 {published data only}

Hughes JR. Free reprints to increase the return of follow-up questionnaires. Controlled Clinical Trials 1989;10:352.

Hurd 2017 {published data only}

Hurd Madeleine, Linsell Louise, Juszczak Ed, Hewer Oliver, Bowler Ursula, Johnson Samantha, Dorling Jon. Increasing follow-up response among parents of very preterm infants: Personalised contact, external promotion, and web-based questionnaires. Trials 2017;18(Supplement 1):P301. [DOI: ]

Hurd 2019 {published data only}

Hurd Madeleine, Bowler Ursula, Juszczak Ed, Hewer Oliver, Dorling Jon, Johnson Samantha. Managing follow-up among parents of very pre-term infants: Methods to improve questionnaire response rate. Trials 2019;20(Supplement 1):181. [DOI: ]

ISRCTN16437731 2016 {published data only}

ISRCTN16437731. Question-behavior effect and flu vaccination in the over 65s. ISRCTN registry 2016. [DOI: ]

Ives 1990 {published data only}

Ives D, Traven N, Kuller L. Comparison of recruitment strategies for health promotion and disease prevalence in the elderly. American Journal of Epidemiology 1990;132:790.

Jacobson 2016 {published data only}

Jacobson Amanda E, Vesely Sara K, Christian-Rancy Myra, O'Brien Sarah H. Mobile application vs. Paper pictorial blood assessment chart to track menses in young women: A randomized cross-over design. Blood 2016;128(22):1006.

Jiang 2005 {published data only}

Jiang P, Rosenbloom B. Customer intention to return online: price perception, attribute-level performance, and satisfaction unfolding over time. European Journal of Marketing 2005;39(1-2):150-74.

Jobber 2004 {published data only}

Jobber David, Saunders John, Mitchell Vince-Wayne. Prepaid monetary incentive effects on mail survey response. Journal of Business Research 2004;57(4):347-350-347-350. [DOI: ]

Johnson 2014 {published data only}

Johnson Samantha, Seaton Sarah E, Manktelow Bradley N, Smith Lucy K, Field David, Draper Elizabeth S, Marlow Neil, Boyle Elaine M. Telephone interviews and online questionnaires can be used to improve neurodevelopmental follow-up rates. BMC research notes 2014;7((Johnson, Seaton, Manktelow, Smith, Field, Draper, Marlow, Boyle) Department of Health Sciences, University of Leicester, 22-28 Princess Road West, Leicester LE1 6TP, UK. sjj19@le.ac.uk):219-219-. [DOI: ]

Johnson 2015 {published data only}

Johnson Natalie A, Kypri Kypros, Latter Joanna, McElduff Patrick, Attia John, Saitz Richard, Saunders John B, Wolfenden Luke, Dunlop Adrian, Doran Christopher, McCambridge Jim. Effect of telephone follow-up on retention and balance in an alcohol intervention trial.. Preventive medicine reports 2015;2(101643766):746-9-746-9. [DOI: ]

Kato 2021 {published data only}

Kato T, Miura T. The impact of questionnaire length on the accuracy rate of online surveys. Journal of Marketing Analytics 2021;9(2):83-98-83-98. [DOI: 10.1057/s41270-021-00105-y]

Kerin 1974 {published data only}

Kerin RA. Personalization strategies, response rate and response quality in a mail survey. Social Science Quarterly 1974;55:175-81.

Kerin 1977 {published data only}

Kerin RA, Peterson RA. Personalization, respondent anonymity, and response distortion in mail surveys. Journal of Applied Psychology 1977;62(1):86-9.

Kerin 1983 {published data only}

Kerin RA. Effects of preliminary contacts on volunteering in mail surveys: another view. Perceptual and Motor Skills 1983;57:1282.

Kimball 1961 {published data only}

Kimball AE. Increasing the rate of return in mail surveys. Journal of Marketing 1961;25:63-5.

Kimel 2010 {published data only}

Kimel Miriam, McCormak J, Chen W, Brunt K, Runken Michael. A Comparative Trial of Paper-and-Pencil Versus Electronic Administration of the Patient Perception of Migraine Questionnaire-Revised (PPMQ-R). In: 52nd Annual Scientific Meeting of the American-Headache-Society Volume: 50. 2010.

Koetsenruijter 2015 {published data only}

Koetsenruijter J, Lieshout J, Wensing M. Higher monetary incentives led to a lowered response rate in ambulatory patients: a randomized trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2015;68(11):1380-1382-1380-1382. [DOI: 10.1016/j.jclinepi.2015.03.018]

Kundig 2011 {published data only}

Kundig F, Staines A, Kinge T, Perneger TV. Numbering questionnaires had no impact on the response rate and only a slight influence on the response content of a patient safety culture survey: a randomized trial. JOURNAL OF CLINICAL EPIDEMIOLOGY 2011;64(11):1262-1265-1262-1265. [DOI: 10.1016/j.jclinepi.2011.02.008]

Labovitz 2017 {published data only}

Labovitz Jonathan, Patel Neil, Santander Israel. Web-Based Patient Experience Surveys to Enhance Response Rates A Prospective Study.. Journal of the American Podiatric Medical Association 2017;107(6):516-521-516-521. [DOI: ]

Lane 2011 {published data only}

Lane Athene J, Down Liz, Wade Julia, Donovan Jenny, Neal David, Hamdy Freddie. Understanding factors influencing questionnaire response rates to maximise retention in a long term complex intervention trial. Trials 2011;12(SUPPL. 1):A134. [DOI: ]

Lane 2017 {published data only}

Lane Athene, Davis Michael, Wade Julia, Turner Emma, Walsh Eleanor, Metcalfe Chris, Martin Richard, Holding Peter, Bonnington Sue, Neal David. Maximising participant retention and outcome data in a long term cancer trial (protect). Trials 2017;18(Supplement 1):P185. [DOI: ]

Lapane 2007 {published data only}

Lapane KL, Quilliam BJ, Hughes CM. A comparison of two distribution methods on response rates to a patient safety questionnaire in nursing homes. JOURNAL OF THE AMERICAN MEDICAL DIRECTORS ASSOCIATION 2007;8(7):446-452-446-452. [DOI: 10.1016/j.jamda.2007.04.007]

Larsson 1970 {published data only}

Larsson I. Increasing the rate of returns in mail surveys. A methodological study. Didakometry & Sociometry 1970;2:43-70.

Lavender 2009 {published data only}

Lavender JM, Anderson DA. Effect of perceived anonymity in assessments of eating disordered behaviors and attitudes.. International Journal of Eating Disorders 2009;42(6):546-551-546-551. [DOI: 10.1002/eat.20645]

Leece 2004a {published data only}

Leece P. Correction and republication: Internet versus mailed questionnaires: A controlled [correction of "Randomized"] - Comparison (2) (vol 4, pg 6, 2004). JOURNAL OF MEDICAL INTERNET RESEARCH 2004;6(4):85-93-85-93.

Li 2015 {published data only}

Li Y, Wang W, Wu Q, Velthoven MH, Chen L, Du XZ, Zhang YF, Rudan I, Car J. Increasing the response rate of text messaging data collection: a delayed randomized controlled trial. JOURNAL OF THE AMERICAN MEDICAL INFORMATICS ASSOCIATION 2015;22(1):51-64-51-64. [DOI: 10.1136/amiajnl-2014-002845]

Lim 2020 {published data only}

Lim Stephanie L, Yang Jui-Chen, Ehrisman Jessie, Havrilesky Laura J, Reed Shelby D. Are Videos or Text Better for Describing Attributes in Stated-Preference Surveys?.. The patient 2020;13(4):401-408-401-408. [DOI: ]

Liu 2011 {published data only}

Liu S T, Geidenberger C. Comparing Incentives to Increase Response Rates Among African Americans in the Ohio Pregnancy Risk Assessment Monitoring System. MATERNAL AND CHILD HEALTH JOURNAL 2011;15(4):527-33.

Longworth 1953 {published data only}

Longworth DS. Use of a mail questionnaire. American Sociologist 1953;18:310-3.

Lopez‐ Cano 2007 {published data only}

Lopez-Cano M, Vilallonga R, Sanchez JL, Hermosilla E, Armengol M. Short postal questionnaire and selective clinical examination combined with repeat mailing and telephone reminders as a method of follow-up in hernia surgery. Hernia 2007;11:397-402.

Lund 1988 {published data only}

Lund DB, Malhotra NK, Smith AE. Field validation study of conjoint analysis using selected mail survey response rate facilitators. Journal of Business Research 1988;16:351-68.

Malhotra 2008 {published data only}

Malhotra N. COMPLETION TIME AND RESPONSE ORDER EFFECTS IN WEB SURVEYS. PUBLIC OPINION QUARTERLY 2008;72(5):914-934-914-934. [DOI: 10.1093/poq/nfn050]

Maloshonok 2016 {published data only}

Maloshonok Natalia, Terentev Evgeniy. The impact of visual design and response formats on data quality in a web survey of MOOC students.. Computers in Human Behavior 2016;62:506-515-506-515. [DOI: 10.1016/j.chb.2016.04.025]

Marks 1981 {published data only}

Mark RB. A factorial experiment in stimulating response to mail surveys. In: American Marketing Association Educators Conference. Vol. 47. 1981:398-400.

May 1960 {published data only}

May RC. What approach gets the best return in mail surveys? Industrial Marketing 1960;45:50-1.

McCree‐Hale 2010 {published data only}

McCree-Hale Renicha, De La Cruz Natalie G, Montgomery Ann Elizabeth. Using downloadable songs from Apple iTunes as a novel incentive for college students participating in a Web-based follow-up survey. American journal of health promotion : AJHP 2010;25(2):119-121-119-121.

McDermott 2003 {published data only}

McDermott MM, Greenland P, Hahn EA, Brogan D, Cella D, Ockene J, Pet al. The effects of continuing medical education credits on physician response rates to a mailed questionnaire. Health Marketing Quarterly 2003;20(4):27-42.

McDermott 2018 {published data only}

McDermott L, Cornelius V, Wright AJ, Burgess C, Forster AS, Ashworth M, Khoshaba B, Clery P, Fuller F, Miller J, Dodhia H, Rudisill C, Conner MT, Gulliford MC. Enhanced Invitations Using the Question-Behavior Effect and Financial Incentives to Promote Health Check Uptake in Primary Care. ANNALS OF BEHAVIORAL MEDICINE 2018;52(7):594-605-594-605. [DOI: 10.1093/abm/kax048]

Mehta 1995 {published data only}

Mehta R, Sivadas E. Comparing response rates and response content in mail versus electronic mail surveys. Journal of the Market Research Society 1995;37:429-39.

Millar 2021 {published data only}

Millar MM, Olson LM, VanBuren JM, Richards R, Pollack MM, Holubkov R, Berg RA, Carcillo JA, McQuillen PS, Meert KL, Mourani PM, Burd RS. Incentive delivery timing and follow-up survey completion in a prospective cohort study of injured children: a randomized experiment comparing prepaid and postpaid incentives. BMC MEDICAL RESEARCH METHODOLOGY 2021;21(1):233. [DOI: 10.1186/s12874-021-01421-8]

Murdoch 2010 {published data only}

Murdoch Maureen, Pietila Diane M, Partin Melissa R. Randomized trial showed that an "embedded" survey strategy optimized authorization rates compared with two "after survey" strategies in veterans with PTSD.. Journal of clinical epidemiology 2010;63(6):665-71-665-71. [DOI: ]

Myers 2007 {published data only}

Myers RP, Shaheen AAM, Lee SS. Impact of pharmaceutical industry versus university sponsorship on survey response: A randomized trial among Canadian hepatitis C care providers. CANADIAN JOURNAL OF GASTROENTEROLOGY 2007;21(3):169-175-169-175. [DOI: 10.1155/2007/945630]

Neve 2021 {published data only}

Neve OM, Benthem PPG, Stiggelbout AM, Hensen EF. Response rate of patient reported outcomes: the delivery method matters. BMC MEDICAL RESEARCH METHODOLOGY 2021;21(1):220. [DOI: 10.1186/s12874-021-01419-2]

Nitecki 1975 {published data only}

Nitecki DA. Effects of sponsorship and nonmonetary incentive on response rate. Journalism Quarterly 1975;55:581-3.

Nitikman 2015 {published data only}

Nitikman M, Mulpuri K, Reilly C. Paper versus internet administration of questionnaires in an adolescent idiopathic scoliosis population: A randomized crossover study. Journal of Investigative Medicine 2015;63(1):198-198-. [DOI: ]

Nitikman 2017 {published data only}

Nitikman M, Mulpuri K, Reilly CW. Internet-administered Health-related Quality of Life Questionnaires Compared With Pen and Paper in an Adolescent Scoliosis Population: A Randomized Crossover Study. JOURNAL OF PEDIATRIC ORTHOPAEDICS 2017;37(2):E75-E79-E75-E79.

Nord 2007 {published data only}

Nord Mark, Hopwood Heather. Does interview mode matter for food security measurement? Telephone versus in-person interviews in the Current Population Survey Food Security Supplement. Public Health Nutrition 2007;10(12):1474-1480-1474-1480. [DOI: ]

O'Toole 2008 {published data only}

O'Toole Joanne, Sinclair Martha, Leder Karin. Maximising response rates in household telephone surveys.. BMC medical research methodology 2008;8(100968545):71-71-. [DOI: ]

Oden 1999 {published data only}

Oden L, Price JH. Effects of a small monetary incentive and follow-up mailings on return rates of a survey to nurse practitioners. Psychological Reports 1999;85:1154-6.

Onoye 2012 {published data only}

Onoye Jane M, Goebert Deborah A, Nishimura Stephanie T. Use of incentives and web-based administration for surveying student alcohol and substance use in an ethnically diverse sample. Journal of Substance Use 2012;17(1):61-71-61-71. [DOI: ]

Otzen 2020 {published data only}

Otzen Tamara, Fuentes Natalia, Wetzel Gustavo, Henríquez Constanza, Antúnez Zayra, Melnik Tamara. Suicidabilidad y apoyo social percibido en estudiantes universitarios con enfermedades crónicas no transmisibles. Ter. psicol 2020;38(1):119-129-119-129. [DOI: 10.4067/S0718-48082020000100119]

Palmer 2018 {published data only}

Palmer Cristina, Farhan Bilal, Nguyen Nobel, Zhang Lishi, Do Rebecca, Nguyen Danh V, Ghoniem Gamal. Are Electronic and Paper Questionnaires Equivalent to Assess Patients with Overactive Bladder?.. The Journal of urology 2018;200(2):369-374-369-374. [DOI: ]

Pariyo 2019 {published data only}

Pariyo George W, Greenleaf Abigail R, Gibson Dustin G, Ali Joseph, Selig Hannah, Labrique Alain B, Al Kibria Gulam Muhammed, Khan Iqbal Ansary, Masanja Honorati, Flora Meerjady Sabrina, Ahmed Saifuddin, Hyder Adnan A. Does mobile phone survey method matter? Reliability of computer-assisted telephone interviews and interactive voice response non-communicable diseases risk factor surveys in low and middle income countries.. PloS one 2019;14(4):e0214450-e0214450-. [DOI: ]

Perneger 2003 {published data only}

Perneger TV, Kossovsky MP, Cathieni F, Florio VD, Burnand B. A randomized trial of four patient satisfaction questionnaires. Medical Care 2003;41(12):1343–52.

Perneger 2014 {published data only}

Perneger TV, Cullati S, Rudaz S, Agoritsas T, Schmidt RE, Combescure C, Courvoisier DS. Effect of numbering of return envelopes on participation, explicit refusals, and bias: experiment and meta-analysis. BMC MEDICAL RESEARCH METHODOLOGY 2014;14:6. [DOI: 10.1186/1471-2288-14-6]

Peytremann‐Bridevaux 2006a {published data only}

Peytremann-Bridevaux I, Scherer F, Peer L, Cathieni F, Bonsack C, Cléopas A, et al. Satisfaction of patients hospitalised in psychiatric hospitals: a randomised comparison of two psychiatric-specific and one generic satisfaction questionnaires. BMC Health Services Research 2006;6(108):1-9.

Pieper 2018 {published data only}

Pieper D, Kotte N, Ober P. The effect of a voucher incentive on a survey response rate in the clinical setting: a quasi-randomized controlled trial. BMC MEDICAL RESEARCH METHODOLOGY 2018;18:86. [DOI: 10.1186/s12874-018-0544-4]

Porter 2004 {published data only}

Porter SR, Whitcomb ME. Understanding the effect of prizes on response rates. New Directions for Institutional Research 2004;121:51-62.

Pottick 1991 {published data only}

Pottick KJ, Lerman P. Maximising survey response rates for hard-to-reach inner-city populations. Social Science Quarterly 1991;721:172-80.

Prado 2012 {published data only}

Prado Cristiana Soares, Tenório Josceli Maria, Ruiz Evandro Eduardo Seron, Ortolani Cristina Lúcia Feijó, Pisa Ivan Torres. Impacto da utilização de mensagens do tipo SMS (Short Message Service) como lembrete na adesão ao tratamento de saúde: revisão sistemática da literatura. J. health inform 2012;4(4):159-64.

Rafiq 2016 {published data only}

Rafiq M, Hussain Z, Akhtar S. Modifications of some simple one-stage randomized response models to two-stage in complex surveys. Pakistan Journal of Statistics and Operation Research 2016;12(2):327-338-327-338. [DOI: 10.18187/pjsor.v12i2.830]

Rashidian 2008 {published data only}

Rashidian A, Meulen J, Russell I. Differences in the contents of two randomized surveys of GPs' prescribing intentions affected response rates. JOURNAL OF CLINICAL EPIDEMIOLOGY 2008;61(7):718-721-718-721. [DOI: 10.1016/j.jclinepi.2007.10.019]

Richards 2009 {published data only}

Richards Julie, Ahrens Kym, Sandler Paula, Richardson Laura. Surveying adolescents enrolled in a regional health plan: Mail & phone followup - What works at what cost? Journal of Adolescent Health 2009;44(2 SUPPL. 1):S37-S37-. [DOI: ]

Richards 2010 {published data only}

Richards J, Wiese C, Katon W, Rockhill C, McCarty C, Grossman D, McCauley E, Richardson LP. Surveying Adolescents Enrolled in a Regional Health Care Delivery Organization: Mail and Phone Follow-up-What Works at What Cost? JOURNAL OF THE AMERICAN BOARD OF FAMILY MEDICINE 2010;23(4):534-541-534-541. [DOI: 10.3122/jabfm.2010.04.100019]

Robbins 2018 {published data only}

Robbins MW, Grimm G, Stecher B, Opfer VD. A Comparison of Strategies for Recruiting Teachers Into Survey Panels. SAGE OPEN 2018;8(3):1. [DOI: 10.1177/2158244018796412]

Robin 1973 {published data only}

Robin DP, Nash HW, Jones SR. An analysis of monetary incentives in mail questionnaire studies. J Business Comm 1973;11:38-42.

Robin 1976 {published data only}

Robin DP, Walters CG. The effect on return rate of messages explaining monetary incentives in mail questionnaire studies. Journal of the Business Community 1976;13(3):49-54.

Rocheleau 2012 {published data only}

Rocheleau Carissa M, Romitti Paul A, Sherlock Stacey Hockett, Sanderson Wayne T, Bell Erin M, Druschel Charlotte. Effect of survey instrument on participation in a follow-up study: a randomization study of a mailed questionnaire versus a computer-assisted telephone interview.. BMC public health 2012;12(100968562):579-579-. [DOI: ]

Roeher 1963 {published data only}

Roeher GA. Effective techniques in increasing response to mailed questionnaires. Public Opinion Quarterly 1963;27:299-302.

Rudd 1980 {published data only}

Rudd NM, Maxwell NL. Mail survey response rates: effects of questionnaire topic and length and recipients community. Psychological Reports 1980;46:435-40.

Ryan 2018 {published data only}

Ryan Michael S, Leggio Lisa E, Peltier Christopher B, Chatterjee Archana, Barone Michael A, Arenberg Steven, Byerley Julie S, Belkowitz Julia L, Rabalais Gerard P. Recruitment and retention of community preceptors. Pediatrics 2018;142(3):e20180673-e20180673-. [DOI: ]

Salomone 1978 {published data only}

Salomone PR, Miller GC. Increasing the response rates of rehabilitation counselors to mailed questionnaires. Rehabilitation Counseling Bulletin 1978;22:138-41.

Senf 1987 {published and unpublished data}

Senf JH. The option to refuse: a tool in understanding nonresponse in mailed surveys. Evaluation Review 1987;11:775-81.

Shackleton 1982 {published data only}

Shackleton VJ, Wild JM. Effect of incentives and personal contact on response rate to a mailed questionnaire. Psychological Reports 1982;50:365-6.

Shah 2016 {published data only}

Shah Kalpit N, Hofmann Martin R, Schwarzkopf Ran, Pourmand Deeba, Bhatia Nitin N, Rafijah Gregory, Bederman S Samuel. Patient-Reported Outcome Measures: How Do Digital Tablets Stack Up to Paper Forms? A Randomized, Controlled Study.. American journal of orthopedics (Belle Mead, N.J.) 2016;45(7):E451-E457-E451-E457.

Shermis 1982 {published data only}

Shermis MD. Issues in survey data quality: four field experiments. Doctoral Dissertation 1982;University of Michigan ProQuest Dissertations Publishing, 1982. 8304591..

Sheth 1975 {published data only}

Sheth JN, Roscoe AM. Impact of questionnaire length, follow-up methods, and geographical location on response rate to a mail survey. Journal of Applied Psychology 1975;60(2):252-4.

Shin 2015 {published data only}

Shin N, Simcoe R, Sule H, Massone R, Hall R. Get feedback now: How to best use your residency management software to increase the response rate and quality of conference evaluations. Western Journal of Emergency Medicine 2015;16(Supplement 1):S13-S14-S13-S14.

Short 2015 {published data only}

Short Camille E, Rebar Amanda L, Vandelanotte Corneel. Do personalised e-mail invitations increase the response rates of breast cancer survivors invited to participate in a web-based behaviour change intervention? A quasi-randomised 2-arm controlled trial.. BMC medical research methodology 2015;15(100968545):66-66-. [DOI: ]

Simcoe 2015 {published data only}

Simcoe Ross, Hall Ronald, Sule Harsh, Massone Richard, Shin Nara. Get feedback now: Increase your survey response rate by using handheld devices, web-based surveys, and protected time for survey completion. Academic Emergency Medicine 2015;22(5 SUPPL. 1):S217-S218-S217-S218. [DOI: ]

Sirken 1960 {published and unpublished data}

Sirken MG, Pifer JW, Brown ML. Survey procedures for supplementing mortality statistics. American Journal of Public Health 1960;50:1753-64.

Smith 1972 {published data only}

Smith EM, Hewett W. The value of a preliminary letter in postal survey response. Journal of the Marketing Research Society 1972;14(3):145-51.

Smith 1977 {published data only}

Smith K. Signing off in the right colour can boost mail survey response. Industrial Marketing 1977;62:61-2.

Smith 1987 {published data only}

Smith K, Bers T. Improving alumni survey response rates: an experiment and cost-benefit analysis. Research in Higher Education 1987;27(3):218-25.

Smith 2019 {published data only}

Smith MG, Witte M, Rocha S, Basner M. Effectiveness of incentives and follow-up on increasing survey response rates and participation in field studies. BMC MEDICAL RESEARCH METHODOLOGY 2019;19(1):230. [DOI: 10.1186/s12874-019-0868-8]

Snyder 1984 {published data only}

Snyder M, Lapovsky D. Enhancing survey response from initial non-consenters. Journal of Advertising Research 1984;24:17-20.

Stenhammar 2011 {published data only}

Stenhammar Christina, Bokström Pär, Edlund Birgitta, Sarkadi Anna. Using different approaches to conducting postal questionnaires affected response rates and cost-efficiency. JOURNAL OF CLINICAL EPIDEMIOLOGY 2011;64(10):1137-1143-1137-1143. [DOI: ]

Suhre 1989 {published and unpublished data}

Surhe C. Schools over the gangway: an experiment on response impoving procedures. Tijdschrift voor Onderwijsresearch 1989;14:172-80.

Sullivan 1995 {published data only}

Sullivan LM, Dukes KA, Harris L, Dittus RS, Greenfield S, Kaplan SH. A comparison of various methods of collecting self-reported health outcomes data among low-income and minority patients. Medical Care 1995;33(4):AS183-94.

Sutherland 1996 {published data only}

Sutherland HJ, Beaton M, Mazer R, Kriukov V, Boyd NF. A randomized trial of the total design method for the postal follow-up of women in a cancer prevention trial. European Journal of Cancer Prevention 1996;5:165-8.

Tan 1997 {published data only}

Tan RT, Burke FJT. Response rates to questionnaires mailed to dentists. A review of 77 publications. International Dental Journal 1997;47:349-54.

TCTR20190814001 2019 {published data only}

TCTR20190814001. Comparison of collecting patient-reported outcome measurements between electronic-based and paper-based questionnaire in adults with low back pain: a randomized controlled crossover trial. WHO International Clinical Trials Registry Platform (ICTRP) 2019.

Trice 1985 {published data only}

Trice AD. Maximizing participation in surveys: hotel ratings VII. Journal of Social Behaviour and Personality 1985;1(1):137-41.

Tucker‐Seeley 2009 {published data only}

Tucker-Seeley Kevon R. The effects of using Likert vs. Visual Analogue Scale response options on the outcome of a web-based survey of 4th through 12th grade students: Data from a randomized experiment.. Dissertation Abstracts International Section A: Humanities and Social Sciences 2009;69(11-A):4305-4305-.

Udby 2021 {published data only}

Udby CL, Riis A, Thomsen JL, Rolving N. Does the use of telephone reminders to increase survey response rates affect outcome estimates? An ancillary analysis of a prospective cohort study of patients with low back pain. BMC Musculoskeletal Disorders 2021;22(1):893. [DOI: 10.1186/s12891-021-04787-4]

Van Ryswyk 2016 {published data only}

Van Ryswyk E M, Middleton P F, Hague W M, Crowther C A. Women's views on postpartum testing for type 2 diabetes after gestational diabetes: Six month follow-up to the DIAMIND randomised controlled trial.. Primary care diabetes 2016;10(2):91-102-91-102. [DOI: ]

von Allmen 2019 {published data only}

Allmen RS, Tinner C, Schmidli J, Tevaearai HT, Dick F. Randomized controlled comparison of cross-sectional survey approaches to optimize follow-up completeness in clinical studies. PLOS ONE 2019;14(3):e0213822.. [DOI: 10.1371/journal.pone.0213822]

Walker 1977 {published data only}

Walker BJ, Burdick RK. Advance correspondence and error in mail surveys. Journal of Marketing Research 1977;14:379-82.

Wang 2018 {published data only}

Wang Mengyang. Grid Questions and Data Quality: An Investigation of Grid Placement on Web Surveys Completed across Three Types of Device. ProQuest Dissertations and Theses 2018;(10841678):187-187-.

Ward 1994 {published data only}

Ward J, Wain G. Increasing response rates of gynaecologists to a survey: a randomised trial of telephone prompts. Australian Journal of Public Health 1994;18(3):332-4.

Warnock 2022 {published data only}

Warnock AC, Kaur H, Buckman JR, Hoenemeyer T, Demark-Wahnefried W. A comparison of two mail-based strategies to recruit older cancer survivors into a randomized controlled trial of a lifestyle intervention. JOURNAL OF CANCER SURVIVORSHIP 2022 ;16(5):998-1003. [DOI: 10.1007/s11764-021-01091-x]

Watson 1965 {published data only}

Watson JJ. Improving the response rate in mail research. Journal of Advertising Research 1965;5:48-50.

Weiss 1985 {published data only}

Weiss LI, Friedman D, Shoemaker CL. Prepaid incentives yield higher response rates to mail surveys. Marketing News 1985;19:30-1.

Weissenburger 1987 {published data only}

Weissenburger FE. Effects of prior information on teacher ratings of students with behaviour problems. Doctoral Dissertation 1987.

Weston 2017 {published data only}

Weston D, Parsons V, Ntani G, Rushton L, Madan I. Mixed contact methods to improve response to a postal questionnaire.. Occupational Medicine 2017;67(4):305-307-305-307. [DOI: ]

Wildman 1977 {published data only}

Wildman RC. Effects of anonymity and social setting on survey responses. Public Opinion Quarterly 1977;41:74-9.

Willis 2013 {published data only}

Willis Gordon B, Smith Tenbroeck, Lee Hyunshik J. Do Additional Recontacts to Increase Response Rate Improve Physician Survey Data Quality? Medical care 2013;51(10):945-8.

Wood 2017 {published data only}

Wood J, Cook JA, Hudson J, McDonald A, Bruhn H, Watson AJM. Do higher monetary incentives improve response rates part-way through a randomised control trial? TRIALS 2017;18:P65.

Zagumny 1996 {published data only}

Zagumny MJ, Ramsey R, Upchurch MP. Is anonymity important in AIDS survey research? Psychological Reports 1996;78:270.

Zheng 2018 {published data only}

Zheng Guili, Oksuzyan Sona, Hsu Shelly, Cloud Jennifer, Jewell Mirna Ponce, Shah Nirvi, Smith Lisa V, Frye Douglas, Kuo Tony. Self-Reported Interest to Participate in a Health Survey if Different Amounts of Cash or Non-Monetary Incentive Types Were Offered.. Journal of Urban Health 2018;95(6):837-849-837-849. [DOI: 10.1007/s11524-018-0237-7]

Ziegenfuss 2012a {published data only}

Ziegenfuss Jeanette Y, Burmeister Kelly R, Harris Ann, Holubar Stefan D, Beebe Timothy J. Telephone follow-up to a mail survey: when to offer an interview compared to a reminder call.. BMC medical research methodology 2012;12(100968545):32-32-. [DOI: ]

Zuidgeest 2011 {published data only}

Zuidgeest Marloes, Hendriks Michelle, Koopman Laura, Spreeuwenberg Peter, Rademakers Jany. A comparison of a postal survey and mixed-mode survey using a questionnaire on patients' experiences with breast care. Journal of medical Internet research 2011;13(3):e68-e68-.

Zwisler 2004 {published data only}

Zwisler LJET, Jarbol LDE, Lous J. Sporgeskemaundersogelser - hvordan opnar jeg en hoj besvarelsesprocent? Ugeskr Laeger 2004;166(7):575-8.

References to studies awaiting assessment

Alexander 2008 {published data only}

Alexander GL, Divine GW, Couper MP, McClure JB, Stopponi MA, Fortman KK, et al. Effect of incentives and mailing features on online health program enrolment. American Journal of Preventive Medicine 2008;34(5):382-8.

Balabanis 2007 {published data only}

Balabanis G, Mitchell VW, Heinonen-Mavrovouniotis S. SMS-based surveys: Strategies to improve participation. International Journal of Advertising 2007;26(3):369-85.

Bauman 2016 {published data only}

Bauman A, Phongsavan P, Cowle A, Banks E, Jorm L, Rogers K, et al. Maximising follow-up participation rates in a large scale 45 and Up Study in Australia. EMERGING THEMES IN EPIDEMIOLOGY 2016;13:6.

Bhattarai 2010 {published data only}

Bhattarai B, Fosgate G T. Increased response proportions for postal questionnaires in Texas veterinarians using incentives. PREVENTIVE VETERINARY MEDICINE 2010;93(1):62-5.

Bosnjak 2015 {published data only}

Bosnjak M, Neubarth W, Couper MP, Bandilla W, Kaczmirek L. Prenotification in web-based access panel surveys: the influence of mobile text messaging versus e-mail on response rates and sample composition. Social Science Computer Review 2015;26(2):213-223.

Brusseleers 2019 {published data only}

Brusseleers M. The ICU Feedback Study: comparing response rate of paper based questionnaires versus electronic questionnaires in patients with a recent intensive care stay. ANZCTR 2019.

Burns 2015 {published data only}

Burns Frances, Clarke Mike, Maguire Lisa. The NICOLA questionnaire trial (NICOLA-QT): A randomised trial of the effect of timing and mode of delivery on the completion and return of a self-assessment questionnaire. Trials 2015;16(Supplement 2):P107.

Damberg 2020 {published data only}

Damberg C, Bogart A, Orr N, Elliott M, Flora Sheng Y, Zaslavsky A. Simplified notifications improve response rates to patient surveys: Findings from the medicare disenrollment survey experiment. Health Services Research 2020;55(SUPPL 1):108.

Davidson 2019 {published data only}

Davidson T, Cooper D. Trial questionnaire response rates-Is bigger better? Trials 2019;20(Supplement 1):579.

Dommeyer 2008 {published data only}

Dommeyer CJ. The effects of the researcher's physical attractiveness and gender on mail survey response. Psychology & Marketing 2008;25(1):47-70.

Dudas 2012 {published data only}

Dudas D, Hudson D, Kirkland E. Methods used to achieve a high response to cancer prevention study-II (CPS-II) mailings. American Journal of Epidemiology 2012;175(SUPPL. 11):S18.

Duncan 2015 {published data only}

Duncan A, Bonetti D, Clarkson J, Ramsay C. Improving trial questionnaire response rates using behaviour change theory. Trials 2015;16(Supplement 2):P92.

Duncan 2017 {published data only}

Duncan A, Goulao B, Ramsay C, Fee P, McLaren-Neil F, Floate R, et al. When is enough, enough? Replication of behaviour change interventions to minimise attrition of follow up questionnaires. Trials 2017;18(Supplement 1):200.:P428.

Edelman 2013a {published data only}

Edelman Linda S, Guymon Maughan, Yang Rumei, Olson Lenora. Improving Response Rates for Surveys of Rural Community Dwelling Older Adults. Communicating Nursing Research 2013;46:338.

Epperson 1997 {published data only}

Epperson WV, Peck RC. Questionnaire response bias as a function of respondent anonymity. Accident Analysis & Prevention 1997;9:249-56.

Finkelstein 2016 {published data only}

Finkelstein Stanley M, Celebrezze Margaret, Cady Rhonda, Lunos Scott, Looman Wendy S. Strategies to Maximize Data Collection Response Rates in a Randomized Control Trial Focused on Children with Medical Complexity. Telemedicine journal and e-health : the official journal of the American Telemedicine Association 2016;22(4):295-301.

Goodman 2017 {published data only}

Goodman K, Hagen S, McClurg D, Sergenson N, Stratton S, Treweek S. Can behaviour change theory increase questionnaire response rates within trials? Trials 2017;18(Supplement 1):200.P439.

Griffin 2019 {published data only}

Griffin Charlotte, Toomey Elaine, Queally Michelle, Hayes Catherine, Kearney Patricia M, Matvienko-Sikar Karen. Influence of providing information to participants about development of trial outcomes on response rates and attitudes to questionnaire completion: Protocol for a study within a trial. HRB open research 2019;2(101754913):2.

Ho‐A‐Yun 2007 {published data only}

Ho-A-Yun J, Crawford F, Newton J, Clarkson J. The effect of advance telephone prompting in a survey of general dental practitioners in Scotland: a randomised controlled trial. Community Dental Health 2007;24(4):233-7.

Hopkins 1983 {published data only}

Hopkins KD, Podolak J. Class-of-mail and the effects of monetary gratuity on the response rates of mailed questionnaires. Journal of Experimental Education 1983;51:169-70.

ISRCTN16642368 2016 {published data only}

ISRCTN16642368. Timing of text message prompts to increase trial participant response to postal questionnaires in UK-FROST. Cochrane Database of Systematic Reviews 2016.

ISRCTN31304930 2014 {published data only}

ISRCTN31304930. Contacting by telephone prior to dispatching postal questionnaires increases response rates in a senescent and frail patient population. Cochrane Central Register of Controlled Trials 2014.

ISRCTN99859966 2018 {published data only}

ISRCTN99859966. Postal questionnaire data collection pilot study - APPEAL pilot study. ISRCTN Registry 2018.

Joinson 2007 {published data only}

Joinson Adam N, Reips Ulf-Dietrich. Personalized salutation, power of sender and response rates to Web-based surveys. Computers in Human Behavior 2007;23(3):1372-83.

Kaplowitz 2011 {published data only}

Kaplowitz, Michael D, Lupi, Frank, Couper, Mick P, et al. The Effect of Invitation Design on Web Survey Response Rates. Social Science Computer Review;30(3):339-349.

Kelly 2010 {published data only}

Kelly Bridget J, Fraze Taressa K, Hornik Robert C. Response rates to a mailed survey of a representative sample of cancer patients randomly drawn from the Pennsylvania Cancer Registry: a randomized trial of incentive and length effects. BMC medical research methodology 2010;10(100968545):65.

Koitsalu 2018 {published data only}

Koitsalu M, Eklund M, Adolfsson J, Gronberg H, Brandberg Y. Effects of pre-notification, invitation length, questionnaire length and reminder on participation rate: a quasi-randomised controlled trial. BMC MEDICAL RESEARCH METHODOLOGY 2018;18(1):3.

Kozak 2020 {published data only}

Kozak Margaret, Usoz Melissa, Fujimoto Dylann, von Eyben Rie, Kidd Elizabeth. Prospective Randomized Trial of Email and/or Telephone Reminders to Enhance Vaginal Dilator Compliance in Patients Undergoing Brachytherapy for Gynecologic Malignancies. International Journal of Radiation Oncology Biology Physics 2020;108(2 Supplement):E10.

Langeland 2019 {published data only}

Langeland JL. The Use of eMail in Establishment Surveys. Dissertation 2019:186.

Maynard 1996 {published data only}

Maynard ML. Effectiveness of 'begging' as a persuasive tactic for improving response rate on a client / agency mail survey. Psychological Reports 1996;78:204-6.

McCrohan 1981 {published data only}

McCrohan KF, Lowe LS. A cost/benefit approach to postage used on mail questionnaires. Journal of Marketing 1981;45:130-3.

Mendoza 2014 {published data only}

Mendoza CA. Variations in online survey designs. Dissertation 2014:146.

Muñoz‐Leiva 2010 {published data only}

Muñoz-Leiva Francisco, Sánchez-Fernández Juan, Montoro-Ríos Francisco, Ibáñez-Zapata José Ángel. Improving the response rate and quality in Web-based surveys through the personalization and frequency of reminder mailings. Quality & Quantity 2010;44(5):1037-52.

Newton 1998 {published data only}

Newton K, Stein SM, Lucey C. Influence of mailing strategies on response to questionnaires. Psychiatric Bulletin 1998;22:692-4.

O'Keefe 1987 {published data only}

O'Keefe LB. Selecting cost-effective survey methods: foot-in-door and prepaid monetary incentives. Journal of Business Research 1987;15:365-76.

Parast 2018 {published data only}

Parast Layla, Elliott Marc N, Hambarsoomian Katrin, Teno Joan, Anhang Price Rebecca. Effects of Survey Mode on Consumer Assessment of Healthcare Providers and Systems (CAHPS) Hospice Survey Scores. Journal of the American Geriatrics Society 2018;66(3):546-52.

Patrick 2021 {published data only}

Patrick Megan E, Couper Mick P, Parks Michael J, Laetz Virginia, Schulenberg John E. Comparison of a web-push survey research protocol with a mailed paper and pencil protocol in the Monitoring the Future panel survey. Addiction (Abingdon, England) 2021;116(1):191-9.

Porter 2007 {published data only}

Porter SR, Whitcomb ME. Mixed-mode contacts in Web surveys: paper is not necessarily better. Public Opinion Quarterly 2007;71(4):635-48.

Price 2004a {published data only}

Price JH, Yingling F, Walsh E, Murnan J, Dake JA. Tone of postcards in increasing survey response rates. Psychological Reports 2004a;94(2):444-8.

Price 2004b {published data only}

Price JH, Yingling F, Walsh E, Murnan J, Dake JA. Tone of postcards in increasing survey response rates. Psychological Reports 2004b;94(2):444-8.

Price 2004c {published data only}

Price JH, Yingling F, Walsh E, Murnan J, Dake JA. Tone of postcards in increasing survey response rates. Pyschological Reports 2004c;94(2):444-8.

Price 2006 {published data only}

Price JH, Dake JA, Jordan TR, Silvestri KS, Ward BL. Effects of small monetary incentives on return rates of a health survey to adults in rural areas. PSYCHOLOGICAL REPORTS 2006;98(3):849-852-849-852. [DOI: 10.2466/PR0.98.3.849-852]

Rach 1994 {unpublished data only}

Rach PJ. An analysis of factors effecting initial response rates to mailed questionnaires. Doctoral Dissertation 1994.

Samel‐Kowalik 2012 {published data only}

Samel-Kowalik P, Raciborski F, Tomaszewska A, Walkiewicz A, Borowicz J, Lusawa A, et al. Impact of the announcement letter on declaration of asthma, rhinitis and eczema in ECAP study. Allergy: European Journal of Allergy and Clinical Immunology 2012;67(SUPPL. 96):606.

Siera 1988 {published data only}

Siera S and Pettibone TJ. Four methods of following up mailed questionnaires. In: Paper presented at the Annual Meeting of the American Educational Research Association. 1988.

Strickland 1980 {published data only}

Strickland S. The effect of wording and scale format on student response to educational evaluation questionnaires. Doctoral Dissertation 1980.

Treat 1996 {published data only}

Treat JB. The effect of questionnaire length on response. Procedings of the Section on Survey, American Statistical Association 1996;1:734-9.

Virtanen 2007 {published data only}

Virtanen Vesa, Sirkiä Timo, Jokiranta Virve. Reducing Nonresponse by SMS Reminders in Mail Surveys. SOCIAL SCIENCE COMPUTER REVIEW 2007;25(3):384-95.

Wood 2015 {published data only}

Wood J, Bruhn H, Cook J A, McDonald A, Norrie J, Watson A J. STRATEGIES TO IMPROVE RESPONSE RATES TO PATIENT REPORTED OUTCOME MEASURES IN A SURGICAL RCT. GUT 2015;64:A161-2.

Additional references

Armstrong 1995

Armstrong BK, White E, Saracci R. Principles of exposure measurement in epidemiology. In: Kelsey JL, Marmot MG, Stolley PD, Vessey MP, editors(s). Monographs in Epidemiology and Biostatistics. First edition. Vol. 21. New York: Oxford University Press Inc., 1995:294-321.

Butler 2013

Butler CC, Simpson SA, Hood K, Cohen D, Pickles T, Spanou C, et al. Training practitioners to deliver opportunistic multiple behaviour change counselling in primary care: a cluster randomised trial.. BMJ 2013;346:f1191.

Clarke 1994

Clarke MJ, Stewart LA. Obtaining data from randomised controlled trials: how much do we need for reliable and informative meta-analyses? BMJ 1994;309:1007-10.

Covidence [Computer program]

Covidence. Melbourne, Australia: Veritas Health Innovation, accessed 7 February 2022. Available at covidence.org.

Edwards 2004

Edwards P, Roberts I, Sandercock P, Frost C. Follow-up by mail in clinical trials: does questionnaire length matter? Controlled Clinical Trials 2004;25(1):31-52.

Edwards 2005

Edwards P, Cooper R, Roberts I, Frost C. Meta-analysis of randomised trials of monetary incentives and response to mailed questionnaires. Journal of Epidemiology and Community Health 2005;59:987-99.

Edwards 2005b

Edwards P, Arango M, Balica L, Cottingham R, El-Sayed H, Farrell, B, et al. Final results of MRC CRASH, a randomised placebo-controlled trial of intravenous corticosteroid in adults with head injury-outcomes at 6 months.. Lancet 2005;365(9475):1957-9.

Egger 1997

Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple graphical test. BMJ 1997;315:629-34.

Free 2011

Free C, Knight R, Robertson S, Whittaker R, Edwards P, Zhou W, et al. Smoking cessation support delivered via mobile phone text messaging (TXT2STOP): a single-blind, randomised trial.. Lancet 2011;378(9785):49-55.

Higgins 2003

Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. BMJ 2003;327(7414):557-60. [DOI: 10.1136/bmj.327.7414.557] [PMID: ]

Higgins 2011

Higgins JP, Altman DG, Gøtzsche PC, Jüni P, Moher D, Oxman AD, et al. The Cochrane Collaboration's tool for assessing risk of bias in randomised trials. BMJ 2011 ;343:d5928.

Higgins 2022

Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.3 (updated February 2022). Cochrane, 2022. vailable from www.training.cochrane.org/handbook.

Hook 1992

Hook EB, Regal RR. The value of capture-recapture methods even for apparently exhaustive surveys. American Journal of Epidemiology 1992;135:1060-7.

Molm 2010

Molm LD. The Structure of Reciprocity. Social Psychology Quarterly 2010;73(2):119-131.

Nakash 2006

Nakash RA et al. Maximising response to postal questionnaires – A systematic review of randomised trials in health research. BMC Medical Research Methodology 2006;6:5.

Price 2022

Price RA et al. A Systematic Review of Strategies to Enhance Response Rates and Representativeness of Patient Experience Surveys. Med Care 2022;60:910–918.

Review Manager 2020 [Computer program]

Review Manager 5 (RevMan 5). Version 5.4. Copenhagen: The Cochrane Collaboration, 2020.

Schulz 1995

Schulz KF, Chalmers I, Hayes RJ, Altman DG. Dimensions of methodological quality associated with estimates of treatment effects in controlled trials. JAMA 1995;273(5):408-12.

Scott 2006

Scott P, Edwards P. Personally addressed hand-signed letters increase questionnaire response: a meta-analysis of randomised controlled trials. BMC Health Services Research 2006;6:111.

Van Gelder 2010

Van Gelder MMHJ, Reini W Bretveld RW, Nel Roeleveld N. Web-based Questionnaires: The Future in Epidemiology? Am J Epidemiol 2010;172:1292-1298.

Yammarino 1991

Yammarino FJ, Skinner SJ, Childers TL. Understanding mail survey response behaviour: a meta-analysis. Public Opinion Quarterly 1991;55:613-39.

References to other published versions of this review

Edwards 2002

Edwards P, Clarke M, DiGuiseppi C, Pratap S, Wentz R, Kwan I. Increasing response rates to postal questionnaires: systematic review. BMJ 2002;324(7347):1183-5.

Edwards 2003

Edwards PJ, Roberts IG, Clarke M, DiGuiseppi C, Pratap S, Wentz R, et al. Methods to increase response rates to postal questionnaires. Cochrane Database of Systematic Reviews 2003, Issue 4. Art. No: MR000008. [DOI: 10.1002/14651858.MR000008.pub2]

Edwards 2007

Edwards PJ, Roberts IG, Clarke MJ, DiGuiseppi C, Wentz R, Kwan I, Cooper R, Felix L, Pratap S. Methods to increase response rates to postal questionnaires. Cochrane Database of Systematic Reviews 2007, Issue 2. Art. No: MR000008. [DOI: 10.1002/14651858.MR000008.pub3]

Edwards 2009

Edwards PJ, Roberts I, Clarke MJ, Diguiseppi C, Wentz R, Kwan I, Cooper R, Felix LM, Pratap S. Methods to increase response to postal and electronic questionnaires. Cochrane Database of Systematic Reviews 2009, Issue 3. Art. No: MR000008. [DOI: 10.1002/14651858.MR000008.pub4] [PMID: ]