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
- U Kiltz1,
- D van der Heijde2,
- A Boonen3,
- A Cieza4,
- G Stucki5,6,7,
- M A Khan8,
- W P Maksymowych9,
- H Marzo-Ortega10,
- J Reveille11,
- S Stebbings12,
- C Bostan6,7,
- J Braun1
- 1Rheumazentrum Ruhrgebiet, Herne, Germany
- 2Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands
- 3Division of Rheumatology, Department of Internal Medicine, Maastricht University Medical Center, and Caphri Research Institute, Maastricht, The Netherlands
- 4eFaculty of Social and Human Sciences, Schools of Psychology, University of Southampton, Southampton, UK
- 5Department of Health Sciences and Health Policy, University of Lucerne, Lucerne, Switzerland
- 6Swiss Paraplegic Research, Nottwil, Switzerland
- 7ICF Research Branch in cooperation with the WHO Family of International Classifications Collaborating Centre in Germany (at DIMDI), Munich, Germany
- 8Case Western Reserve University, Cleveland, Ohio, USA
- 9Division of Rheumatology, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
- 10Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds and NIHR Leeds Musculoskeletal Biomedical Research Unit, Chapel Allerton Hospital, Leeds, UK
- 11Division of Rheumatology and Clinical Immunogenetics, Department of Medicine, The University of Texas Health Science Center at Houston, Houston, Texas, USA
- 12Department of Medicine, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
- Correspondence to Dr Uta Kiltz, Rheumazentrum Ruhrgebiet, St. Josefs-Krankenhaus, Landgrafenstr. 15, Herne 44652, Germany; uta.kiltz{at}vincenzgruppe.de
- Received 16 May 2013
- Revised 14 November 2013
- Accepted 10 December 2013
- Published Online First 7 January 2014
Abstract
Objectives 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.
