title: Development of a health index in patients with ankylosing spondylitis (ASAS HI): final result of a global initiative based on the ICF guided by ASAS.
abstract: OBJECTIVE
  The burden of disease in patients with ankylosing spondylitis (AS) can be considerable. However, no agreement has been reached among expert members of Assessment of SpondyloArthritis International Society (ASAS) to define severity of AS. Based on the International Classification of Functioning, Disability and Health (ICF), a core set of items for AS has been selected to represent the entire spectrum of possible problems in functioning. Based on this, the objective of this study was to develop a tool to quantify health in AS, the ASAS Health Index.
  
  
  METHODS
  First, based on a literature search, experts' and patients' opinion, a large item pool covering the categories of the ICF core set was generated. In several steps this item pool was reduced based on reliability, Rasch analysis and consensus building after two cross-sectional surveys to come up with the best fitting items representing most categories of the ICF core set for AS.
  
  
  RESULTS
  After the first survey with 1754 patients, the item pool of 251 items was reduced to 82. After selection by an expert committee, 50 items remained which were tested in a second cross-sectional survey. The results were used to reduce the number of items to a final set of 17 items. This selection showed the best reliability and fit to the Rasch model, no residual correlation, and absence of consistent differential item function and a Person Separation Index of 0.82.
  
  
  CONCLUSIONS
  In this long sequential study, 17 items which cover most of the ICF core set were identified that showed the best representation of the health status of patients with AS. The ASAS Health Index is a linear composite measure which differs from other measures in the public domain.
authors.affiliation: Rheumazentrum Ruhrgebiet, Herne, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Kiltz
authors.affiliation: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: D
authors.initials: D
authors.lastname: van der Heijde
authors.affiliation: Division of Rheumatology, Department of Internal Medicine, Maastricht University Medical Center, and Caphri Research Institute, Maastricht, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Boonen
authors.affiliation: eFaculty of Social and Human Sciences, Schools of Psychology, University of Southampton, Southampton, UK.
authors.forename: A
authors.initials: A
authors.lastname: Cieza
authors.affiliation: Department of Health Sciences and Health Policy, University of Lucerne, Lucerne, Switzerland Swiss Paraplegic Research, Nottwil, Switzerland ICF Research Branch in cooperation with the WHO Family of International Classifications Collaborating Centre in Germany (at DIMDI), Munich, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Stucki
authors.affiliation: Case Western Reserve University, Cleveland, Ohio, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Khan
authors.affiliation: Division of Rheumatology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: W P
authors.initials: WP
authors.lastname: Maksymowych
authors.affiliation: Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Chapel Allerton Hospital, Leeds, UK.
authors.forename: H
authors.initials: H
authors.lastname: Marzo-Ortega
authors.affiliation: Division of Rheumatology and Clinical Immunogenetics, Department of Medicine, The University of Texas Health Science Center at Houston, Houston, Texas, USA.
authors.forename: J
authors.initials: J
authors.lastname: Reveille
authors.affiliation: Department of Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand.
authors.forename: S
authors.initials: S
authors.lastname: Stebbings
authors.affiliation: Swiss Paraplegic Research, Nottwil, Switzerland ICF Research Branch in cooperation with the WHO Family of International Classifications Collaborating Centre in Germany (at DIMDI), Munich, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Bostan
authors.affiliation: Rheumazentrum Ruhrgebiet, Herne, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Braun
mesh_terms: D000203:Activities of Daily Living; D000223:Adaptation, Psychological; D000328:Adult; D000368:Aged; D032921:Consensus; D003430:Cross-Sectional Studies; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D013167:Spondylitis, Ankylosing / Q000503:physiopathology* / Q000523:psychology; D011795:Surveys and Questionnaires
keywords: Ankylosing Spondylitis; Outcomes research; Spondyloarthritis