Structural and construct validity of the Whiplash Disability Questionnaire in adults with acute whiplash-associated disorders

BACKGROUND CONTEXT: Few instruments are available to measure disability associated with whiplash-associated disorders (WAD). The Whiplash Disability Questionnaire (WDQ) was developed to measure disability resulting from WAD, but its validity is unknown for acute WAD. PURPOSE: The aim was to determine the structural and construct validity of the WDQ in individuals with acute WAD. STUDY DESIGN/SETTING: This was a cohort study. PATIENT SAMPLE: Ontario adults with WAD were enrolled within 3 weeks of their motor vehicle collision. OUTCOME MEASURES: The outcome measure was the WDQ. METHODS: We included insurance claimants who were aged 18 years or older and diagnosed with acute WAD Grades I to III. All participants completed the WDQ, a 13-item questionnaire scored from 0 (no disability) to 130 (complete disability). We assessed the factor structure of the WDQ and tested its construct validity against self-perceived recovery, neck pain (Numerical Rating Scale [NRS]), neck disability (Neck Disability Index [NDI] and Neck Bournemouth Questionnaire), health-related quality of life (36-Item Short Form Health Survey [SF-36]), and depressive symptoms (Center for Epidemiologic Studies Depression Scale [CES-D]). RESULTS: The mean age of the 130 participants was 42.1 years (standard deviation [SD]=13.2), and 70% were women. Twenty-six percent had WAD I, 73.1% had WAD II, and 0.8% had WAD III. Mean time since injury was 6.5 days (SD=4.9). The mean WDQ score was 49.8 (SD=29.1). Our analysis suggested that the WDQ includes two factors: daily activities and emotional status. This factor structure remained stable in sensitivity analyses (eg, zeros imputed for missing values, and the item with the most missing values or resulting in complex loading excluded). Strong correlations were found between the total WDQ score and the NDI, the Bournemouth questionnaire, the SF-36 physical function, and the NRS (for the neck, shoulder, mid and low back pain) satisfying a priori hypotheses. We found a priori hypothesized moderate correlations between the WDQ, and the CES-D and SF-36 mental function. CONCLUSIONS: The WDQ includes two factors and has strong construct validity in individuals with acute WAD. Our results demonstrate that the WDQ is valid for use as an overall summative scale or as the daily activities and emotional subscales in clinical and research settings to determine disability status