An examination of intrasubject variability on the Dysphonia Severity Index.

OBJECTIVES/HYPOTHESIS: The purpose of this study was to expand on previous literature regarding the intrasubject variability of the Dysphonia Severity Index (DSI) by incorporating a larger sample of participants and by examining the test-retest mean differences and intrasubject variability not only in the DSI but also within its component measures.

STUDY

DESIGN

Longitudinal and within-subject design.

METHODS

The DSI and component measures of jitter, maximum phonation time (MPT), lowest vocal intensity, and highest phonational frequency (F(0)) were obtained from 49 normal voiced participants (21 males and 28 females) between the ages of 18-25 years. Each participant was tested in three testing sessions with an approximate 1-week interval between each testing session.

RESULTS

These results indicated that the mean DSI and its component measures of high F(0) and MPT are quite stable across time (ie, no significant differences across time and strong intraclass correlation coefficients [ICCs]), whereas Bland-Altman analyses indicated that the within-subject 1-week test-retest variability on the DSI for normal voiced subjects may be expected to be within ±2.27, and the 2-week test-retest variability may be expected to be within ±2.66. In addition, weak ICC results indicated that increased variability may also be expected in the DSI component measures of low decibel and jitter. No evidence of a test-practice effect on repeated DSI measurements was observed.

CONCLUSIONS

The findings of this study are in agreement with previous data regarding the intrasubject variability of the DSI. Changes in DSI that exceed ±2.27-2.66 may be necessary to reflect significant changes in voice function. The observed test-retest variability in the DSI is relatively large in relation to the initially reported DSI range of +5 (normal voice) to -5 (severely disordered voice). Rather than the use of ±2 standard deviations (SDs) as a guideline for significant change (±2.27-2.66), DSI change of ±1.5 SDs may be clinically useful, resulting in a more liberal level of ±1.74 (within 1 week) to 2.04 (within 2 weeks) as a guideline for significant changes in voice function.