title: Psychometric properties of the Veterans Affairs Low-Vision Visual Functioning Questionnaire.
abstract: OBJECTIVE
  To describe psychometric properties of a self-report questionnaire, the Veterans Affairs (VA) Low-Vision Visual Functioning Questionnaire (LV VFQ-48), which was designed to measure the difficulty visually impaired persons have performing daily activities and to evaluate low-vision outcomes.
  
  
  METHODS
  The VA LV VFQ-48 was administered by telephone interview to subjects with visual acuity ranging from near normal to total blindness at five sites in the VA and private sector. Rasch analysis with the Andrich rating scale model was applied to difficulty ratings from 367 subjects, to evaluate measurement properties of the instrument.
  
  
  RESULTS
  High intercenter correlations for item measure estimates (intraclass correlation coefficient [ICC]=0.97) justified pooling the data from these sites. The person measure fit statistics (mean square residuals) confirm that the data fit the assumptions of the model. The item measure fit statistics indicate that responses to 19% of the items were confounded by factors other than visual ability. The separation reliabilities for pooled data (0.94 for persons and 0.98 for items) demonstrate that the estimated measures discriminate persons and items well along the visual ability dimension. ICCs for test-retest data (0.98 for items and 0.84 for persons) confirm temporal stability. Subjects used the rating categories in the same way at all five centers. Ratings of slight and moderate difficulty were used interchangeably, suggesting that the instrument could be modified to a 4-point scale including not difficult, slightly/moderately difficult, extremely difficult, and impossible. Fifty additional subjects were administered the questionnaire with a 4-point scale to confirm that the scale was used in the same way when there were four rather than five difficulty ratings.
  
  
  CONCLUSIONS
  The VA LV VFQ-48 is valid and reliable and has the range and precision necessary to measure visual ability of low-vision patients with moderate to severe vision loss across diverse clinical settings.
authors.affiliation: Blind Rehabilitation Center, Edward Hines VA Hospital, Hines, Illinois 60141, USA. joan.stelmack@med.va.gov
authors.forename: Joan A
authors.initials: JA
authors.lastname: Stelmack
authors.forename: Janet P
authors.initials: JP
authors.lastname: Szlyk
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Stelmack
authors.forename: Paulette
authors.initials: P
authors.lastname: Demers-Turco
authors.forename: R Tracy
authors.initials: RT
authors.lastname: Williams
authors.forename: D'Anna
authors.initials: D
authors.lastname: Moran
authors.forename: Robert W
authors.initials: RW
authors.lastname: Massof
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D011795:Surveys and Questionnaires; D014481:United States; D014493:United States Department of Veterans Affairs; D015351:Vision Screening / Q000295:instrumentation*; D015354:Vision, Low / Q000503:physiopathology* / Q000534:rehabilitation; D014792:Visual Acuity / Q000502:physiology*