A test-retest reliability study of the whiplash disability questionnaire in patients with acute whiplash-associated disorders
OBJECTIVE: The purpose of this study was to determine the test-retest reliability and the Minimal Detectable Change (MDC) of the Whiplash Disability Questionnaire (WDQ) in individuals with acute whiplash-associated disorders (WADs). METHODS: We performed a test-retest reliability study. We included insurance claimants from Ontario who were at least 18years of age, within 21days of their motor vehicle collision and diagnosed as having acute WAD grades I to III. The WDQ, a 13-item questionnaire scored from 0 (no disability) to 130 (complete disability), was administered to all participants at baseline and by telephone 3days later. We computed the intraclass correlation coefficient (model 2,1) and the MDC with 95% confidence intervals (CIs; MDC95). RESULTS: The mean (SD) age of the 66 participants was 41.6 (12.7) years and 71.2% were female. Twenty-nine percent had WAD I and 71.2% had WAD II. Time since injury ranged from 0 to 19 days. The mean (SD) baseline WDQ score was 49.3 (28.8) and 46.5 (29.8) 3days later. The intraclass correlation coefficient for the WDQ total score was 0.89 (95% CI, 0.85-0.92) in the entire sample and 0.83 (95% CI, 0.69-0.93) for the 15 participants reporting no change in neck pain. The MDC95 of the WDQ was 21.4 (SD = 14.9) for participants reporting no change. CONCLUSION: The WDQ was reliable in individuals with acute WAD. There is 95% confidence that a change of approximately one-sixth of the total score is beyond the daily variation of a stable condition. This level of measurement error must be taken into consideration when interpreting change in WDQ scores