 |
|
|
 |
A Model to Estimate Health Utilities Index Mark 3 Utility Scores from WOMAC Index Scores in Patients with Osteoarthritis of the Knee
PAUL GROOTENDORST, DEBORAH MARSHALL, DAN PERICAK, NICHOLAS BELLAMY, DAVID FEENY, and GEORGE W. TORRANCE ABSTRACT. Objective. To develop a formula to translate Western Ontario and McMaster University Osteoarthritis Index (WOMAC) scores collected in clinical trials of patients with osteoarthritis (OA) into Health Utilities Index Mark 3 (HUI3) utility scores for application in economic evaluation. Methods. Data from a previously published open-label randomized controlled trial of appropriate care with hylan G-F 20 versus appropriate care without hylan G-F 20 in 255 outpatients with knee OA. We estimated linear regression models of HUI3 scores using various functions of WOMAC, demographics, and clinical variables. Out-of-sample predictive performance of the models was assessed using the mean absolute error and several other criteria. Results. The preferred formula included WOMAC pain, stiffness, function subscales, demographic variables; it accounted for almost 40% of the variation in the HUI3 utility scores. At the group level, absolute differences between predicted and actual overall HUI3 utility scores were < 0.001 and not statistically significantly different from zero. Conclusion. A formula was derived from the WOMAC index to estimate overall utility scores based on the HUI3 for studies of patients with OA for whom utility has not been recorded. Researchers can estimate overall utility scores, compute quality-adjusted life-years, and perform cost-utility analyses within a defined range of certainty. (J Rheumatol 2007;34:534–42) Key Indexing Terms:
OSTEOARTHRITIS From the Faculty of Pharmacy, University of Toronto, Toronto; Department of Economics, McMaster University, Hamilton; Department of Health Economics and Outcomes Research, i3 Innovus, Burlington; Health Utilities Inc., Dundas, Ontario; Departments of Economics and Public Health Sciences, University of Alberta, and Institute for Health Economics, Edmonton, Alberta, Canada; The University of Queensland, Centre of National Research on Disability and Rehabilitation Medicine (CONROD), Queensland, Australia; and Kaiser Permanente Northwest Center for Health Research, Portland, Oregon, USA. Supported by the Alberta Improvements for Musculoskeletal Disorders Study (AIMS). AIMS was initiated by the Alberta Ministry of Health to improve the care and quality of life for patients with acute and chronic musculoskeletal disorders and is funded by unrestricted grants from Merck Frosst Canada Inc. and Pfizer Canada Ltd. An independent advisory committee was assembled to oversee the study design, analysis, and interpretation of the findings. i3 Innovus is an independent health economics research organization responsible for the design and execution of the study. The authors thank Genzyme Corporation for permitting the data from the hylan G-F study1 to be used for this study. D. Feeny and G. Torrance have a proprietary interest in Health Utilities Incorporated, Dundas, ON, Canada. HUInc. owns the copyright to and distributes HUI materials. N. Bellamy has a proprietary interest in WOMACTM and owns the copyright and trademark to and distributes WOMAC materials. P. Grootendorst, PhD, Associate Professor, Leslie Dan Faculty of Pharmacy, University of Toronto; D. Marshall, PhD, VP,Global Health Economics and Outcomes Research, i3 Innovus; D. Pericak, MMath, PStat, Senior Manager, Health Economics and Outcomes Research, i3 Innovus; N. Bellamy, MD, MSc, MBA, DSc, FRCPC, FRCP (Glas, Edin), FACP, FRACP, Professor and Director, CONROD, The University of Queensland; D. Feeny, PhD, Center for Health Research, Northwest/Hawai'i/Southeast Kaiser Permanente Northwest Region; G.W. Torrance, PhD, Professor Emeritus, McMaster University and Principal Consultant, i3 Innovus. Address reprint requests to D. Pericak, Health Economics and Outcomes Research, i3 Innovus, 1016-A Sutton Drive, Burlington, Ontario L7L 6B8, Canada. E-mail: dan.pericak@i3innovus.com Accepted for publication November 9, 2006.
|
