title: The refractive status and vision profile: Rasch analysis of subscale validity.
abstract: OBJECTIVE
  To determine whether the eight subscales of the Refractive Status and Vision Profile (RSVP) questionnaire provide valid measurement.
  
  
  METHODS
  Two hundred patients, recruited from a refractive surgery clinic and general optometric practice, self-administered the 42-item RSVP questionnaire. Psychometric properties investigated included measurement of a single construct (unidimensionality), item fit to construct, measurement precision (represented by person separation), targeting of item difficulty to patient's quality of life (QOL), and differential item functioning.
  
  
  RESULTS
  Only two subscales ("concern" and "driving") showed adequate person separation, indicating that they could discriminate patients' QOL. However, both demonstrated poor targeting (7.02 logits for "driving" and 1.11 logits for "concern"). One-third of items in each subscale suffered from differential item functioning.
  
  
  CONCLUSIONS
  None of the RSVP subscales are valid for assessment of QOL in patients with refractive error, thereby indicating the RSVP should be considered as a single questionnaire without subscales.
authors.affiliation: Department of Optometry and Vision Science, Flinders University of South Australia, Bedford Park, Australia.
authors.forename: Vijaya K
authors.initials: VK
authors.lastname: Gothwal
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Wright
authors.forename: David B
authors.initials: DB
authors.lastname: Elliott
authors.forename: Konrad
authors.initials: K
authors.lastname: Pesudovs
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001334:Automobile Driving; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology*; D011594:Psychometrics; D011788:Quality of Life; D012029:Refraction, Ocular / Q000502:physiology*; D018434:Sickness Impact Profile; D011795:Surveys and Questionnaires; D014785:Vision, Ocular / Q000502:physiology*