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.