title: Validity and internal consistency of a whiplash-specific disability measure.
abstract: METHODS
  Cross-sectional study of patients with whiplash-associated disorders investigating the internal consistency, factor structure, response rates, and presence of floor and ceiling effects of the Whiplash Disability Questionnaire (WDQ).
  
  
  OBJECTIVE
  The aim of this study was to confirm the appropriateness of the proposed WDQ items.
  
  
  BACKGROUND
  Whiplash injuries are a common cause of pain and disability after motor vehicle accidents. Neck disability questionnaires are often used in whiplash studies to assess neck pain but lack content validity for patients with whiplash-associated disorders. The newly developed WDQ measures functional limitations associated with whiplash injury and was designed after interviews with 83 patients with whiplash in a previous study.
  
  
  METHODS
  Researchers sought expert opinion on items of the WDQ, and items were then tested on a clinical whiplash population. Data were inspected to determine floor and ceiling effects, response rates, factor structure, and internal consistency. Packages of questionnaires were distributed to 55 clinicians, whose patients with whiplash completed and returned 101 questionnaires to researchers.
  
  
  RESULTS
  No substantial floor or ceiling effects were identified on inspection of data. The overall floor effect was 12%, and the overall ceiling effect was 4%. Principal component analysis identified one broad factor that accounted for 65% of the variance in responses. Internal consistency was high; Cronbach's alpha = 0.96.
  
  
  CONCLUSIONS
  Results of the study supported the retention of the 13 proposed items in a whiplash-specific disability questionnaire. Dependent on the results of further psychometric testing, the WDQ is likely to be an appropriate outcome measure for patients with whiplash.
authors.affiliation: School of Physiotherapy, La Trobe University, Victoria, Australia.
authors.forename: Melanie
authors.initials: M
authors.lastname: Pinfold
authors.forename: Ken R
authors.initials: KR
authors.lastname: Niere
authors.forename: Elizabeth F
authors.initials: EF
authors.lastname: O'Leary
authors.forename: Jan Lucas
authors.initials: JL
authors.lastname: Hoving
authors.forename: Sally
authors.initials: S
authors.lastname: Green
authors.forename: Rachelle
authors.initials: R
authors.lastname: Buchbinder
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D011795:Surveys and Questionnaires; D014911:Whiplash Injuries