title: Measuring Health-Related Quality of Life in Strabismus: A Modification of the Adult Strabismus-20 (AS-20) Questionnaire Using Rasch Analysis.
abstract: OBJECTIVE
  To evaluate the psychometric properties of the Adult Strabismus-20 (AS-20)- a health-related quality of life (HRQoL) questionnaire in adults with strabismus, and if flawed, to revise the AS-20 and its subscales creating valid measurement scales.
  
  
  METHODS
  584 adults (meanage, 27.5 years) with strabismus were recruited from an outpatient clinic at a South Indian tertiary eye care centre and were administered the AS-20 questionnaire.The AS-20 was translated and back translated into two Indian languages. The AS-20 and its two 10-item subscales - 'psychosocial' and 'function'were assessed separately for fit to the Rasch model, including an assessment of the rating scale, unidimensionality (by principal components analysis), measurement precision by person separation reliability, PSR, targeting, and differential item functioning (DIF; notable > 1.0 logits).
  
  
  RESULTS
  Response categories were not used as intended, thereby, required re-organization and reducing their number from 5 to 3. The AS-20 had adequate measurement precision (PSR = 0.87) but lacked unidimensionality; however, deletion of the six multi-dimensionality causing items and an additional three misfitting items resulted in 11-item unidimensional questionnaire (AS-11). Two items failed to satisfy the model expectations in the 'psychosocial' subscale and were deleted - resulting in an 8-item unidimensional scale with adequate PSR (0.81) and targeting (0.23 logits). One item misfit in the 'function' subscale and was deleted-resulting in a 9 item Rasch-revised unidimensional subscale with acceptable PSR (0.80) and targeting (0.97 logits).None of the items displayed notable DIF by age, gender and level of education.
  
  
  CONCLUSIONS
  The AS-11 and its two Rasch-revised subscales - 8-item psychosocial and 9-item function subscale may be more appropriate than the original AS-20 and its two 10-item subscales for use as unidimensional measures of HRQoL in adults with strabismus in India. Further work is required to establish the validity of the revised rating scale.
authors.affiliation: Meera and L B Deshpande Centre for Sight Enhancement, L V Prasad Eye Institute, KallamAnji Reddy campus, Hyderabad, India.
authors.forename: Vijaya K
authors.initials: VK
authors.lastname: Gothwal
authors.affiliation: Meera and L B Deshpande Centre for Sight Enhancement, L V Prasad Eye Institute, KallamAnji Reddy campus, Hyderabad, India.
authors.forename: Seelam
authors.initials: S
authors.lastname: Bharani
authors.affiliation: Jasti V Ramanamma Children's Eye Care Centre, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Kekunnaya
authors.affiliation: Jasti V Ramanamma Children's Eye Care Centre, L V Prasad Eye Institute, Hyderabad, India.
authors.forename: PreetiPatil
authors.initials: P
authors.lastname: Chhablani
authors.affiliation: Nimmagadda Prasad Children's Eye Care Centre, L V Prasad Eye Institute, GMR Varalakshmi Campus, Vishakapatnam, India.
authors.forename: Virender
authors.initials: V
authors.lastname: Sachdeva
authors.affiliation: The David Brown Children's Eye Care Centre, KodeVenkatadriChowdary Campus, Vijayawada, India.
authors.forename: Niranjan K
authors.initials: NK
authors.lastname: Pehere
authors.affiliation: The David Brown Children's Eye Care Centre, KodeVenkatadriChowdary Campus, Vijayawada, India.
authors.forename: Asa
authors.initials: A
authors.lastname: Narasaiah
authors.affiliation: Nimmagadda Prasad Children's Eye Care Centre, L V Prasad Eye Institute, GMR Varalakshmi Campus, Vishakapatnam, India.
authors.forename: Rekha
authors.initials: R
authors.lastname: Gunturu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D011336:Probability; D011594:Psychometrics; D011788:Quality of Life; D013285:Strabismus / Q000503:physiopathology*; D011795:Surveys and Questionnaires; D055815:Young Adult