title: Evaluation of the Adult Strabismus-20 (AS-20) questionnaire using Rasch analysis.
abstract: OBJECTIVE
  To further refine the Adult Strabismus 20 (AS-20) health-related quality of life (HRQOL) questionnaire using Rasch analysis.
  
  
  METHODS
  Rasch analysis was performed independently on the original AS-20 using the following steps: dimensionality, response ordering, local dependence, infit and outfit analyses, differential item functioning, subject targeting, and confirmatory dimensionality.
  
  
  RESULTS
  Two subscales were present in each of the original AS-20 subscales, for a total of 4 subscales, which were labeled "self-perception," "interaction," "reading function," and "general function." Response ordering was appropriate for 3 of the subscales but required reduction to 4 response options for the fourth subscale. No notable local dependence was found for any subscale. As a result of fit analysis, 2 items were removed, 1 each from 2 subscales. No significant differential item functioning was seen for sex or age. The resulting 5-item self-perception subscale and 4-item reading function subscale are reliable and target the adult strabismus patient cohort appropriately. The resulting 5-item interaction subscale and 4-item general function subscale have less than optimal reliability.
  
  
  CONCLUSIONS
  The AS-20 benefits from reduction to 4 subscales (self-perception, interaction, reading function, and general function) and reducing the response options in the general function subscale from 5 to 4 options. The refined AS-20 may prove to be even more responsive to HRQOL changes in adult strabismus following treatment or changes over time.
authors.affiliation: Department of Ophthalmology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Leske
authors.forename: Sarah R
authors.initials: SR
authors.lastname: Hatt
authors.forename: Laura
authors.initials: L
authors.lastname: Liebermann
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Holmes
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006302:Health Services Research; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D018434:Sickness Impact Profile; D013285:Strabismus / Q000523:psychology*; D011795:Surveys and Questionnaires; D055815:Young Adult