Objectives To evaluate construct validity, interpretability, reliability and responsiveness as well as determination of cut-off points for good and poor health within the original English version and the 18 translations of the disease-specific Assessment of Spondyloarthritis international Society Health Index (ASAS HI) in 23 countries worldwide in patients with spondyloarthritis (SpA).
Methods A representative sample of patients with SpA fulfilling the ASAS classification criteria for axial (axSpA) or peripheral SpA was used. The construct validity of the ASAS HI was tested using Spearman correlation with several standard health outcomes for axSpA. Test–retest reliability was assessed by intraclass correlation coefficients (ICCs) in patients with stable disease (interval 4–7 days). In patients who required an escalation of therapy because of high disease activity, responsiveness was tested after 2–24weeks using standardised response mean (SRM).
Results Among the 1548 patients, 64.9% were men, with a mean (SD) age 42.0 (13.4) years. Construct validity ranged from low (age: 0.10) to high (Bath AnkylosingSpondylitisFunctioning Index: 0.71). Internal consistency was high (Cronbach’s α of 0.93). The reliability among 578 patients was good (ICC=0.87 (95% CI 0.84 to 0.89)). Responsiveness among 246 patients was moderate-large (SRM=−0.44 for non-steroidal anti-inflammatory drugs, −0.69 for conventional synthetic disease-modifying antirheumatic drug and −0.85 for tumour necrosis factor inhibitor). The smallest detectable change was 3.0. Values ≤5.0 have balanced specificity to distinguish good health as opposed to moderate health, and values ≥12.0 are specific to represent poor health as opposed to moderate health.
Conclusions The ASAS HI proved to be valid, reliable and responsive. It can be used to evaluate the impact of SpA and its treatment on functioning and health. Furthermore, comparison of disease impact between populations is possible.
- ankylosing spondylitis
- outcomes research
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Handling editor Tore K Kvien
Contributors Study concept and design: UKU, DvdH, AB, JB. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Writing of the manuscript: UKU. Critical revision of the manuscript for important intellectual content: all authors. All authors had access to the data, commented on the report drafts and approved the final submitted version.
Funding This study was funded by the Assessment of Spondyloarthritis international Society (ASAS).
Competing interests None declared.
Patient consent Obtained.
Ethics approval All centres received approval from their local ethics committee.
Provenance and peer review Not commissioned; externally peer reviewed.
Correction notice This article has been corrected since it published Online First. The acknowledgements statement has been updated.