title: Lookup Tables Versus Stacked Rasch Analysis in Comparing Pre- and Postintervention Adult Strabismus-20 Data.
abstract: OBJECTIVE
  We compare two methods of analysis for Rasch scoring pre- to postintervention data: Rasch lookup table versus de novo stacked Rasch analysis using the Adult Strabismus-20 (AS-20).
  
  
  METHODS
  One hundred forty-seven subjects completed the AS-20 questionnaire prior to surgery and 6 weeks postoperatively. Subjects were classified 6 weeks postoperatively as "success," "partial success," or "failure" based on angle and diplopia status. Postoperative change in AS-20 scores was compared for all four AS-20 domains (self-perception, interactions, reading function, and general function) overall and by success status using two methods: (1) applying historical Rasch threshold measures from lookup tables and (2) performing a stacked de novo Rasch analysis. Change was assessed by analyzing effect size, improvement exceeding 95% limits of agreement (LOA), and score distributions.
  
  
  RESULTS
  Effect sizes were similar for all AS-20 domains whether obtained from lookup tables or stacked analysis. Similar proportions exceeded 95% LOAs using lookup tables versus stacked analysis. Improvement in median score was observed for all AS-20 domains using lookup tables and stacked analysis (P< 0.0001 for all comparisons).
  
  
  CONCLUSIONS
  The Rasch-scored AS-20 is a responsive and valid instrument designed to measure strabismus-specific health-related quality of life. When analyzing pre- to postoperative change in AS-20 scores, Rasch lookup tables and de novo stacked Rasch analysis yield essentially the same results.
  
  
  CONCLUSIONS
  We describe a practical application of lookup tables, allowing the clinician or researcher to score the Rasch-calibrated AS-20 questionnaire without specialized software.
authors.affiliation: Department of Ophthalmology Mayo Clinic, Rochester, MN, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Leske
authors.affiliation: Department of Ophthalmology Mayo Clinic, Rochester, MN, USA.
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Hatt
authors.affiliation: Department of Ophthalmology Mayo Clinic, Rochester, MN, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Liebermann
authors.affiliation: Department of Ophthalmology Mayo Clinic, Rochester, MN, USA.
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Holmes
keywords: Rasch; patient reported outcomes; quality of life; strabismus; surgery