There are shortcomings of valid questionnaires for measuring functional limitations in patients with Whiplash Associated Disorders (WAD), since existing measures are not suitable for addressing the specific limitations of these patients and because of cross contamination between theoretical constructs. The goal of this study was to evaluate dimensionality, test-retest reliability, measurement error, construct validity, and responsiveness of a new condition-specific questionnaire for WAD and also to estimate the minimally important change score. Patients with WAD grade I or II were recruited from physical therapy practices and rehabilitation centers. Dimensionality was examined by internal consistency analysis (Cronbach’s alpha) and factor analysis. Test-retest reliability was estimated by intraclass correlations and measurement error was calculated by the minimal detectable change (MDC) scores. Construct validity was investigated by testing predefined hypotheses on correlations of the WAL scores with generic health measures and by applying the known group method. Responsiveness was expressed as the minimal clinically important change (MCIC) score. 73 individuals (53 women) were included. Cronbach’s alpha was high (0.95) and unidimensionality was plausible because factor analysis showed 40.3% variance explained by one dominant factor, which was more than 4.5 times larger than the second largest factor. Test-retest reliability was excellent (0.92, 95% CI 0.87–0.95). Construct validity was supported by 14 out of 15 confirmed hypotheses and the WAL showed statistically significant differences between known groups. MDC was 16 points while the MCIC was 18 points.
This study indicates that the WAL has adequate measurement properties, but additional investigation is needed.