Background and purpose: Shoulder scales are often used to evaluate treatment efficacy, yet little is known about the psychometric properties of these scales. Only one scale has undergone psychometric scrutiny: the Shoulder Pain and Disability Index (SPADI). This study compared 2 shoulder measures-the University of California-Los Angeles (UCLA) Shoulder Scale and the Simple Shoulder Test (SST)-with the SPADI.
Subjects: One hundred ninety-two patients with shoulder disorders were recruited from one physician's office to complete the self-report sections of the 3 scales.
Methods: Cronbach alpha values and standard errors of measurement (SEM) were calculated for each of the multi-item subscales. Validity was examined through calculation of correlation coefficients among the 3 scales. Factor analysis was completed to assess the underlying constructs of the SPADI and the SST.
Results: Cronbach alpha values ranged from.85 to.95. The SEM values for the multi-item scales ranged from 4.75 to 11.65. Evidence for validity to reflect function was indicated by the correlation between the SST and the SPADI disability subscale. The factor analysis of the SPADI revealed loading on 1 factor, whereas the SST loaded on 2 factors.
Conclusion and discussion: All scales demonstrated good internal consistency, suggesting that all items for each scale measure the same construct. However, the SEMs for all scales were high. Factor loading was inconsistent, suggesting that patients may not distinguish between pain and function.