Department of Quantitative Health Sciences; Graduate School of Biomedical Sciences, Clinical and Population Health Research Program
Health Services Research | Musculoskeletal Diseases
BACKGROUND: The SF-36 physical functioning scale (PF-10) and the Health Assessment Questionnaire disability index (HAQ-DI) are the most frequently used instruments for measuring self-reported physical function in rheumatoid arthritis (RA). The objective of this study was to develop a crosswalk between scores on the PF-10 and HAQ-DI in RA.
METHODS: Item response theory (IRT) methods were used to co-calibrate both scales using data from 1791 RA patients. The appropriateness of a Rasch-based crosswalk was evaluated by comparing it with crosswalks based on a two-parameter and a multi-dimensional IRT model. The accuracy of the final crosswalk was cross-validated using baseline (n = 532) and 6-month follow-up (n = 276) data from an independent cohort of early RA patients.
RESULTS: The PF-10 and HAQ-DI adequately fit a unidimensional Rasch model. Both scales measured a wide range of functioning, although the HAQ-DI tended to better target lower levels of functioning. The Rasch-based crosswalk performed similarly to crosswalks based on the two-parameter and multidimensional IRT models. Agreement between predicted and observed scale scores in the cross-validation sample was acceptable for group-level comparisons. The longitudinal validity in discriminating between disease response states was similar between observed and predicted scores.
CONCLUSION: The crosswalk developed in this study allows for converting scores from one scale to the other and can be used for group-level analyses in patients with RA.
Health assessment questionnaire, Item response theory, Linking, Physical functioning, Rheumatoid arthritis, Short form 36-item health survey (SF-36)
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Copyright 2013 ten Klooster et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
DOI of Published Version
ten Klooster PM, Oude Voshaar MA, Gandek B, Rose M, Bjorner JB, Taal E, Glas CA, van Riel PL, van de Laar MA. Development and evaluation of a crosswalk between the SF-36 physical functioning scale and Health Assessment Questionnaire disability index in rheumatoid arthritis. Health Qual Life Outcomes. 2013 Nov 15;11:199. doi: 10.1186/1477-7525-11-199. Link to article on publisher's site
Health and quality of life outcomes
ten Klooster, Peter M.; Oude Voshaar, Martijn A. H.; Gandek, Barbara; Rose, Matthias S. F.; Bjorner, Jakob B.; Taal, Erik; Glas, Cees A. W.; van Riel, Piet L. C. M.; and van de Laar, Mart A. F. J., "Development and evaluation of a crosswalk between the SF-36 physical functioning scale and Health Assessment Questionnaire disability index in rheumatoid arthritis" (2013). University of Massachusetts Medical School Faculty Publications. 330.