title: The Activities of Daily Vision Scale for cataract surgery outcomes: re-evaluating validity with Rasch analysis.
abstract: OBJECTIVE
  The Activities of Daily Vision Scale (ADVS) has been extensively validated by traditional methodology. In the current study, Rasch analysis was used to explore further the validity of the ADVS and to determine whether improvements could be made.
  
  
  METHODS
  Forty-three patients with cataract underwent visual acuity (VA) and contrast sensitivity (CS) testing and completed the ADVS. The data were Rasch analyzed and the value of response scale and item reduction explored. A shortened version and the original ADVS were tested for criterion validity by determining correlations with VA and CS.
  
  
  RESULTS
  The ADVS data contained abnormally distributed items and items with ceiling effects and empty response categories. Therefore, items benefited from shortening the response scale, the optimum length being three responses. There was poor targeting of item difficulty to patient ability, because many patients with cataract were sufficiently able that they had no difficulty with many activities. Items were eliminated if the task was too easy or did not fit with the overall concept of visual disability determined by the Rasch model. A reduced ADVS version was established that had adequate precision, equivalent criterion validity, and improved targeting of item difficulty to patient ability, but this version was still not ideal.
  
  
  CONCLUSIONS
  Despite careful traditional validation, the ADVS data contained inadequacies exposed by Rasch analysis. Through Rasch scaling, particularly with response scale reduction, the ADVS can be improved, but additional questions seem to be needed to suit the more able, including patients undergoing second eye cataract surgery. There remains a need to develop Rasch-scaled measures of visual disability for use in ophthalmic outcomes research.
authors.affiliation: Department of Optometry, University of Bradford, Bradford, West Yorkshire, United Kingdom. k.pesudovs@bradfrod.ac.uk
authors.forename: Konrad
authors.initials: K
authors.lastname: Pesudovs
authors.forename: Estibaliz
authors.initials: E
authors.lastname: Garamendi
authors.forename: John P
authors.initials: JP
authors.lastname: Keeves
authors.forename: David B
authors.initials: DB
authors.lastname: Elliott
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D002386:Cataract / Q000503:physiopathology*; D002387:Cataract Extraction; D015350:Contrast Sensitivity / Q000502:physiology; D004185:Disability Evaluation; D015577:Geriatric Assessment; D006304:Health Status; D006801:Humans; D017063:Outcome Assessment, Health Care; D015203:Reproducibility of Results; D014786:Vision Disorders / Q000503:physiopathology*; D015351:Vision Screening / Q000295:instrumentation; D014792:Visual Acuity / Q000502:physiology