Willingness to Pay for a QALY Based on Community Member and Patient Preferences for Temporary Health States Associated with Herpes Zoster
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Background and Objectives: A clear sense of what society is willing to pay for a QALY could enhance the usefulness of cost-effectiveness analysis as a field. Scant information exists on willingness to pay (WTP) for a QALY based on direct elicitation of preferences from community members or patients. We had the opportunity to evaluate WTP per QALY using data from a survey on temporary health outcomes related to herpes zoster. Our aims were to (i) describe how much community members are willing to pay to save a QALY based on scenarios describing temporary health states; (ii) evaluate how WTP per QALY varies based on experience with the disease being described and with demographic variables; and (iii) evaluate how the duration and intensity of pain in a scenario influences WTP per QALY.
Methods: Community members drawn from a nationally representative survey research panel (n = 478) completed an Internet-based survey using time trade-off (TTO) and WTP questions to value a series of scenarios that described herpes zoster cases of varying pain intensity (on a scale of 0–10) and duration (30 days to 1 year). Patients with shingles (n = 354) or postherpetic neuralgia (PHN; n = 120) [defined as having symptoms for 90 days or more] from two large healthcare systems completed telephone interviews with similar questions.
Mean and median WTP per QALY values were calculated by dividing the WTP amount by the discounted time traded for each scenario. Responses with a WTP value of more than zero and a TTO value of zero (which would have resulted in an undefined value) were excluded. TTO values were discounted by 3% per year. WTP per QALY means were calculated after trimming the top and bottom 2.5% of responses. Multivariate analyses were conducted using generalized linear mixed models that assumed a negative binomial distribution.
Results: Among all respondents, the WTP per QALY ranged from a median of $US7000 to $US11 000 and a trimmed mean of $US26 000 to $US45 000 (year 2005 values), depending on the scenario described. WTP per QALY values varied significantly with respondent characteristics, as well as among respondents with similar characteristics. In multivariate analyses, the mean WTP per QALY was higher among respondents who were younger, male or had higher educational or income levels. After adjusting for these demographic variables, patients who had experienced shingles gave responses with the highest WTP per QALY values. Patients who had experienced PHN gave the lowest values, and community members gave values intermediate to the shingles and PHN groups. In multivariate models that evaluated the effects of pain and duration of the hypothetical zoster scenario, lower duration was associated with higher WTP per QALY. This effect appeared to be due to people increasing the amounts of time they would be willing to trade as duration increased, without proportional increases in the amounts of money they would be willing to pay.
Conclusions: Community members and patients gave mean WTP per QALY values that varied significantly based on age, sex, socioeconomic status, experience with shingles and duration of the health state evaluated. The variability in WTP per QALY suggests that it may be difficult to define a unitary threshold of dollars per QALY for policy making based on cost-effectiveness analyses.
KeywordsCommunity Member Herpes Zoster Postherpetic Neuralgia Contingent Valuation Study Temporary Health
This study was supported by the Joint Initiative in Vaccine Economics Project under cooperative agreements (numbers U01IP000029 and U01IP000143) with the Centers for Disease Control and Prevention (CDC). We are grateful to our collaborators in the original Zoster Utilities Evaluation study, including Katherine Yih, PhD; Irene Shui, MPH; Rafael Harpaz, PhD; and Peter Choo, MD, MPH. We thank our CDC programme officer, Mark Messonnier, PhD, for cogent advice and support throughout this research.
The findings and conclusions expressed are those of the authors and do not necessarily represent the views of the CDC or Department of Health and Human Services. G. Thomas Ray has received research funding from Wyeth for an unrelated study and from Merck for a study related to the epidemiology of herpes zoster. All other authors have no conflicts of interest that are directly relevant to the content of this study.
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