title: Visual Activities Questionnaire: assessment of subscale validity for cataract surgery outcomes.
abstract: OBJECTIVE
  To examine the psychometric properties of the Visual Activities Questionnaire (VAQ) and each of its subscales in a modern cataract population using Rasch analysis and if flawed, to revise the VAQ and create a valid measure that maximizes its measurement properties.
  
  
  METHODS
  Flinders Eye Centre, Flinders Medical Centre, Adelaide, Australia.
  
  
  METHODS
  Patients with cataract in 1 or both eyes drawn from the surgical waiting list were mailed the 33-item VAQ for self-administration. The following were examined for the entire questionnaire and each subscale: whether items measured a single construct (unidimensionality), the behavior of response categories, the ability to differentiate between patients' visual abilities (person separation), matching of item difficulty to participant ability (targeting), and whether items function similarly across subgroups of participants (differential item functioning [DIF]).
  
  
  RESULTS
  The VAQ was completed by 561 patients. Response categories were used as intended. The VAQ discriminated the visual ability of the population (person separation, 4.88) but had suboptimum targeting, misfitting items, significant multidimensionality, DIF, and 4 dysfunctional subscales. Elimination of items causing multidimensionality resulted in a reduced 13-item VAQ that met all validity criteria for satisfactory instrument performance. Only 1 valid subscale (peripheral vision) could be preserved in the 13-item VAQ.
  
  
  CONCLUSIONS
  The VAQ in its native form was multidimensional and contained subscales with poor psychometric properties. The revised unidimensional 13-item VAQ was more appropriate for application in cataract outcomes assessment. Ideally, more items should be included to improve the targeting of item difficulty to more able cataract patients.
authors.affiliation: NH&MRC Centre for Clinical Eye Research, Department of Ophthalmology, Flinders Medical Centre and Flinders University of South Australia, Bedford Park, South Australia, Australia.
authors.forename: Vijaya K
authors.initials: VK
authors.lastname: Gothwal
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Wright
authors.forename: Ecosse L
authors.initials: EL
authors.lastname: Lamoureux
authors.forename: Konrad
authors.initials: K
authors.lastname: Pesudovs
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D002386:Cataract / Q000503:physiopathology*; D002387:Cataract Extraction; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D011594:Psychometrics / Q000379:methods; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D015354:Vision, Low / Q000503:physiopathology; D014792:Visual Acuity / Q000502:physiology*