title: A multilevel item response theory model was investigated for longitudinal vision-related quality-of-life data.
abstract: OBJECTIVE
  To investigate how a multilevel item response theory (IRT) model for longitudinal dependent data could provide average and individual quality-of-life outcomes of low-vision rehabilitation.
  
  
  METHODS
  In a nonrandomized longitudinal design, visually impaired older patients (n=296) were referred to multidisciplinary rehabilitation or to an optometric service. The five-dimensional Low Vision Quality of Life Questionnaire was administered at four time points. The IRT model was characterized by the graded response model for rating scales. Covariates were added to the model, mainly to correct for missing data. The invariance assumption across time points was investigated.
  
  
  RESULTS
  Average and individual rehabilitation effects were estimated. For multidisciplinary rehabilitation, significant average deterioration was seen on three dimensions after 4.4 years. Many individuals in the optometric service group significantly improved on the "reading small print" dimension (18.5%); in both groups, many individuals significantly deteriorated on "visual (motor) skills" (22.2-30.0%). Invariance across time points could be assumed for all dimensions, except for "adjustment." Gender, education, visual acuity, and health status were significantly associated with the outcome.
  
  
  CONCLUSIONS
  We present how a multilevel IRT model can be applied to describe longitudinal dependent vision-related quality-of-life data, while focusing on average and individual effects.
authors.affiliation: Department of Ophthalmology, VU University Medical Center Amsterdam, Amsterdam, The Netherlands. r.vannispen@vumc.nl
authors.forename: Ruth M A
authors.initials: RM
authors.lastname: van Nispen
authors.forename: Dirk L
authors.initials: DL
authors.lastname: Knol
authors.forename: Han J
authors.initials: HJ
authors.lastname: Neve
authors.forename: Ger H M B
authors.initials: GH
authors.lastname: van Rens
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D015233:Models, Statistical; D010352:Patient Dropouts / Q000706:statistics & numerical data; D011594:Psychometrics; D011788:Quality of Life; D016896:Treatment Outcome; D015354:Vision, Low / Q000503:physiopathology / Q000534:rehabilitation*; D014792:Visual Acuity