Reproducibility and responsiveness of the Whiplash Disability Questionnaire.
This study continued the validation of a Whiplash Specific Disability Questionnaire (WDQ) that was developed from the Neck Disability Index (NDI) using self-reported disabilities in a group of participants experiencing whiplash-associated disorders [J Manipulative Physiol Ther 14 (1991) 409]. Previous research has established the content, construct and face validity and internal consistency of the WDQ. The aim of this study was to establish the short-term and medium-term test-retest reliability and responsiveness of the WDQ. Participants (n = 63) receiving physiotherapy treatment for WAD were recruited from 30 private physiotherapy practices in Melbourne, Australia. Each participant completed three WDQ questionnaires over a 1-month period, the first two separated by 24 h. The third questionnaire contained an additional item that asked respondents to rate their perceived change in condition over the month. Reproducibility was determined using an intra-class correlation co-efficient. Responsiveness was assessed via correlation with participant perceived change, the effect size, standardised response mean (SRM) and the responsiveness statistic. Results demonstrated excellent short-term test-retest reliability (ICC 0.96). Reproducibility over 1 month was excellent (ICC 0.93). Correlation between change in WDQ score over 1 month and participant perceived change was r(s) = 0.64, the effect size was 0.03, the SRM was 0.08 and the responsiveness statistics were 0.90 (participants who improved) and -1.60 (participants who deteriorated). The minimal detectable change of the WDQ was established at 15 points. These results demonstrate that the WDQ has excellent short- and medium-term reproducibility and responsiveness in a population seeking treatment for WAD.