Measurement properties of the Dutch version of the Western Ontario Shoulder Instability Index (WOSI)

The Western Ontario Shoulder Instability Index (WOSI) is a disease-specific shoulder questionnaire to measure quality of life in patients with shoulder instability. The aim of the present study was to translate the WOSI into Dutch and assess its principal measurement properties. The WOSI was translated into Dutch according to guidelines in the literature. Fifty-two shoulder instability patients completed the questionnaire twice within 2 weeks. We assessed internal consistency (Cronbach’s alpha), test-retest reliability [Intraclass Correlation Coefficient (ICC)], standard error of measurement (SEM), smallest detectable change (SDC) and reliable change index. The Bland-Altman analysis was applied to assess test-retest agreement and floor and ceiling effects were calculated. Cronbach’s alpha was 0.95 for the total WOSI score (range 0.88-0.95 for the 4 domains). ICC for the total WOSI score was 0.91 (range 0.79-0.90 for domains), SEM was 130.6 for the total WOSI score resulting in a SDC of 362.0, which is 17.3 % of the maximum obtainable score of 2100. Bland-Altman analysis showed no systematic differences or consistent bias between the two assessments. We observed no relevant floor and ceiling effects. The results of the present study suggest the Dutch version of the WOSI is a reliable tool for clinical assessment and scientific evaluation. It shows high values for Cronbach’s alpha and ICC implying excellent internal consistency and good test-retest reliability.