Further validation and reliability testing of the Rotator Cuff Quality of Life Index (RC-QOL) according to the Consensus-Based Standards for the Selection of Health Measurement Instruments (COSMIN) guidelines

Abstract

Background: The Rotator Cuff Quality of Life Index (RC-QOL) was developed to evaluate quality of life in patients with rotator cuff disorders (RCD). The purpose of this study was to provide additional reliability, validity, and responsiveness testing in accordance with the Consensus-Based Standards for the Selection of Health Measurement Instruments (COSMIN) guidelines.

Methods: Preliminary patient interviews included 15 patients. Seventy patients (mean age, 58; standard deviation, 9 years) with RCD were evaluated. Methodology testing included internal consistency, test-retest reliability, measurement error, content validity, and construct validity. Responsiveness, interpretability, and generalizability were also analyzed.

Results: The Cronbach α was 0.96 (95% confidence interval, 0.89-0.99; range, 0.72-0.94). The intraclass correlation coefficient for the RC-QOL was 0.87 (95% confidence interval, 0.79-0.85; range, 0.77-0.88). The standard error of measurement was 8 (range, 7-13). The smallest detectable change was 3 (range, 2-4). Content validity was confirmed through standardized patient interviews. All a priori hypotheses were confirmed. No floor or ceiling effects were present. The minimally clinical important difference ranged between 7 and 14 points. The study met the COSMIN criteria for interpretability and generalizability.

Conclusion: The RC-QOL is a reliable and valid measure of health-related quality of life in patients with chronic RCD. The results of this study added to the methodologic quality assessment of the RC-QOL, completing 7 of 10 COSMIN criteria.

Keywords: psychometric assessment; quality of life; reliability; rotator cuff; shoulder; validity.