title: Catquest-9SF patient outcomes questionnaire: nine-item short-form Rasch-scaled revision of the Catquest questionnaire.
abstract: OBJECTIVE
  To assess and optimize the Catquest questionnaire for measuring patient-reported outcomes of cataract surgery using Rasch analysis.
  
  
  METHODS
  Fifty-eight ophthalmic surgical units in Sweden.
  
  
  METHODS
  Catquest questionnaires (n = 21364) from the Swedish National Cataract Register were selected and randomized to 2 groups. Data from 10486 questionnaires were comprehensively Rasch analyzed using a 4-Andrich rating scale model in Winsteps software. A revised version of Catquest was developed (Catquest-9SF) and tested in 10886 patients for validity and responsiveness to cataract surgery.
  
  
  RESULTS
  Only the visual disability subscale formed a valid measurement scale. This could be enhanced through the addition of the 2 global assessment items; however, the symptoms and frequency of performing the activities items did not contribute to the measurement. The 9-item short-form version (Catquest-9SF) had ordered response thresholds and good person separation (2.65) and was largely free from differential item functioning. All items fit a single overall construct (infit range, 0.75 to 1.29; outfit range, 0.70 to 1.39) and unidimensional by principal components analysis. The items were well targeted to the preoperative participants (0.34 logit difference in means). The score correlated with visual acuity (r = 0.43 preoperatively; r = 0.48 postoperatively) and was highly responsive to cataract surgery (preoperatively -0.32 +/- 2.15 logits; postoperatively -3.21 +/- 2.50 logits (P<.0001).
  
  
  CONCLUSIONS
  The 9-item Rasch-scaled Catquest-9SF was highly valid in measuring visual disability outcomes of cataract surgery. Its brevity makes it suited to routine clinical use, and a raw-data to Rasch-measure conversion simplifies application.
authors.affiliation: EyeNet Sweden, Blekinge Hospital, Karlskrona, Sweden. mats.lundstrom@ltblekinge.se
authors.forename: Mats
authors.initials: M
authors.lastname: Lundström
authors.forename: Konrad
authors.initials: K
authors.lastname: Pesudovs
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D000369:Aged, 80 and over; D002386:Cataract / Q000503:physiopathology; D002387:Cataract Extraction; D004185:Disability Evaluation; D005260:Female; D006302:Health Services Research; D006801:Humans; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction; D019591:Pseudophakia / Q000503:physiopathology; D011788:Quality of Life; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D013548:Sweden; D016896:Treatment Outcome; D014785:Vision, Ocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology*