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Do Utility Values and Willingness to Pay Suitably Reflect Health Outcome in Hip and Knee Osteoarthritis? A Comparative Analysis with the WOMAC Index
OLIVIER ETHGEN, ANNALISA TANCREDI, ERIC LEJEUNE, ANGELA KVASZ, BRIGITTE ZEGELS, and JEAN-YVES REGINSTER
ABSTRACT.
Methods. One hundred twenty-eight patients with OA attending a specialized arthritis clinic were interviewed about their socioeconomic characteristics and administered the TTO technique and the WOMAC. Their WTP for 2 hypothetical anti-osteoarthritic drugs was also investigated: the first drug was said to provide a significant improvement in WOMAC dimensions and the second a complete cure of the disease. WTP was elicited by both discrete-choice and bidding game methods. Results. Answer rates were 89.1% for TTO, 98.4% for discrete-choice WTP for both scenarios, and 89.8% and 85.2% for bidding game WTP in the relief and the cure scenario, respectively. The mean TTO utility value was 0.84 (standard deviation 0.20). In discrete-choice, those accepting the bid had higher monthly income (€ 1536.5 vs € 1060.1, p < 0.001, for the relief scenario and € 1449.3 vs € 1071.6, p < 0.001, for the cure scenario). With the bidding game format, WTP was positively correlated with income in both scenarios (r = 0.56, r = 0.55, p < 0.001). WTP measures differed equally between education and socioeconomic groups with those in favored groups consistently reporting higher WTP (Kruskal-Wallis tests statistics ranging from p < 0.01 to p < 0.001). Except for stiffness, WOMAC dimensions were correlated in the expected direction with TTO values (r = –0.27, p < 0.01 for pain and r = –0.36, r = –0.34, p < 0.001 for physical function and total score, respectively). Conclusion. Whereas they showed good feasibility, WTP measures poorly reflected clinical condition and were mainly related to economic status and ability to pay. TTO was correlated with the WOMAC dimensions and may be considered closer to clinical situations than WTP. However, concern arises regarding the homogeneity of the study sample in terms of clinical severity, which may have precluded the identification of a relationship between WTP and clinical status. (J Rheumatol 2003;30:2452-9) Key Indexing Terms:
TIME TRADE-OFF
From the WHO Collaborating Center for Public Health Aspects of Osteoarticular Disorders and the Department of Epidemiology and Public Health, University of Liège — CHU Sart Tilman; and the Bone and Cartilage Research Unit, University of Liège — CHU Centre Ville, Liège, Belgium. O. Ethgen, MSc; A. Tancredi, MSc, WHO Collaborating Center and Department of Epidemiology and Public Health; E. Lejeune, PhD; A. Kvasz, MD; B. Zegels, PhD, Bone and Cartilage Research Unit; J-Y. Reginster, MD, PhD, WHO Collaborating Center, Department of Epidemiology and Public Health, and Bone and Cartilage Research Unit. Address reprint requests to Prof. J-Y. Reginster, Department of Public Health Sciences, University of Liège — CHU Sart Tilman, Avenue de l'Hôpital - Bâtiment B23, 4020 Liège, Belgium. E-mail: jyreginster@ulg.ac.be Submitted September 16, 2002; revision accepted May 13, 2003. |