Development and psychometric validation of the shoulder problems assessment scale.

BACKGROUND

Many shoulder patient-reported outcome measures (PROMs) rely on response categories that may be difficult to interpret in routine care.

OBJECTIVE

To develop and validate the 12-item Shoulder Problems Assessment Scale (SPAS), an activity-based PROM that uses a hierarchical stepwise yes/no format to identify the first threshold of difficulty during daily activities.

METHODS

The study used a multicenter design combining qualitative item development with psychometric testing. Items were generated from patient interviews, literature review, and clinician input, then refined through expert review. Pilot testing (n = 52) supported item refinement. Field testing (n = 415) was conducted at 12 outpatient physical therapy centers. The final SPAS includes 12 activity-based items, each with four ordered difficulty statements scored 4-0. For structural validation, exploratory factor analysis (EFA) and confirmatory factor analysis were performed in separate subsamples (n = 207 and n = 208), respectively. Internal consistency (Cronbach's α), test-retest reliability (intraclass correlation coefficient (ICC(3,1))), convergent validity (Shoulder Pain and Disability Index (SPADI) correlations), and discriminative ability were evaluated using receiver operating characteristic analysis. Analyses followed COSMIN recommendations.

RESULTS

The results of EFA indicated a three-factor structure (Joint Mobility, Functionality, Pain), accounting for 56.16% of the variance. The proposed three-factor structure demonstrated excellent model fit (χ2/df = 1.07, CFI = 0.999, TLI = 0.998, RMSEA = 0.021, SRMR = 0.056). Total-scale internal consistency was α = 0.834; test-retest reliability was excellent (ICC(3,1) = 0.913). The SPAS correlated strongly with SPADI (r = 0.790; p < .001). Discriminative ability was acceptable (area under the curve = 0.862).

CONCLUSION

The SPAS is a 12-item, culturally relevant, activity-based shoulder PROM that uses a hierarchical yes/no response format to identify the activity level at which difficulty first occurs. It may support goal setting and follow-up in routine outpatient physiotherapy by assessing shoulder-related functional limitation.