Purpose: The purpose of this study was to examine the measurement properties of four commonly used disability measures. We hypothesized that all measures would have a high (0.8 or >
0.8) internal consistency and ability to discriminate between men and women’s level of disability. A moderate convergent validity (0.5 to 1.00).
Method: This was a prospective longitudinal study of patients with advanced primary osteoarthritis of glenohumeral joint who underwent a Total Shoulder Arthroplasty (TSA). Four measures [Western Ontario Osteoarthritis Shoulder (WOOS) Index, the American Shoulder and Elbow Surgeon’s (ASES) assessment, Constant-Murley Score (CMS), and Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH)] were completed 2–3 weeks before surgery and at 6 months after surgery. The measurement properties were examined in:
internal consistency as a measure of reliability,
cross-sectional and longitudinal convergent validity,
known group validity, and
sensitivity to change at 6 months following surgery.
Analysis involved calculating Cronbach Coefficient Alpha to measure internal consistency. Convergent validity was examined by the Pearson correlation coefficient. Analysis of Variance examined the extent of known group validity. The Standardized Response Mean (SRM) was used to measure the relative sensitivity to change.
Results: Seventy patients (mean age: 65, range: 35–86, 44 females, 26 males) participated in the study. The Cronbach Coefficient Alpha was high at 0.91, 0.86, and 0.83 for WOOS, ASES, and QuickDASH respectively. Cross-sectional convergent validity was moderate with correlations varying from 0.54 to 0.79. Longitudinal convergent validity ranged from 0.58 to 0.88. All measures were able to discriminate between men and women at p<
0.05 with Cohen’s d of 1.07, 0.85, 0.82, and 0.55 for QuickDASH, CMS, WOOS, and ASES respectively. The SRM was 2.41, 2.17, 1.88, and 1.63 for WOOS, CMS, ASES and QuickDASH respectively.
Conclusion: All four disability measures were valid and reliable in candidates for TSA. The WOOS, a disease-specific outcome demonstrated a higher reliability and sensitivity to change than other measures. QuickDASH had a better ability to differentiate between men and women. Clinicians may not gain additional information by administrating multiple similar outcome measures. Researchers will decrease their chance of declaring a statistical significance by choosing one primary outcome measure.
