title: Application of the health assessment questionnaire disability index to various rheumatic diseases.
abstract: OBJECTIVE
  To investigate whether the Stanford Health Assessment Questionnaire Disability Index (HAQ-DI) can serve as a generic instrument for measuring disability across different rheumatic diseases and to propose a scoring method based on item response theory (IRT) modeling to support this goal.
  
  
  METHODS
  The HAQ-DI was administered to a cross-sectional sample of patients with confirmed rheumatoid arthritis (n = 619), osteoarthritis (n = 125), or gout (n = 102). The results were analyzed using the generalized partial credit model as an IRT model.
  
  
  RESULTS
  It was found that 4 out of 8 item categories of the HAQ-DI displayed substantial differential item functioning (DIF) over the three diseases. Further, it was shown that this DIF could be modeled using an IRT model with disease-specific item parameters, which produces measures that are comparable for the three diseases.
  
  
  CONCLUSIONS
  Although the HAQ-DI partially functioned differently in the three disease groups, the measurement regarding the disability level of the patients can be made comparable using IRT methods.
authors.affiliation: Institute for Behavioral Research, Faculty of Behavioral Sciences, University of Twente, PO Box 217, 7500 AE, Enschede, The Netherlands.
authors.forename: Maaike M
authors.initials: MM
authors.lastname: van Groen
authors.forename: Peter M
authors.initials: PM
authors.lastname: ten Klooster
authors.forename: Erik
authors.initials: E
authors.lastname: Taal
authors.forename: Mart A F J
authors.initials: MA
authors.lastname: van de Laar
authors.forename: Cees A W
authors.initials: CA
authors.lastname: Glas
mesh_terms: D000368:Aged; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011788:Quality of Life; D012216:Rheumatic Diseases / Q000503:physiopathology* / Q000523:psychology; D011795:Surveys and Questionnaires