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 18 years of age, within 21 days 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 3 days 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) 3 days 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.
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