Disentangling WTP per QALY data: different analytical approaches, different answers.
A large random sample of the Danish general population was asked to value health improvements by way of both the time trade-off elicitation technique and willingness-to-pay (WTP) using contingent valuation methods. The data demonstrate a high degree of heterogeneity across respondents in their relative valuations on the two scales. This has implications for data analysis. We show that the estimates of WTP per QALY are highly sensitive to the analytical strategy. For both open-ended and dichotomous choice data we demonstrate that choice of aggregated approach (ratios of means) or disaggregated approach (means of ratios) affects estimates markedly as does the interpretation of the constant term (which allows for disproportionality across the two scales) in the regression analyses. We propose that future research should focus on why some respondents are unwilling to trade on the time trade-off scale, on how to interpret the constant value in the regression analyses, and on how best to capture the heterogeneity in preference structures when applying mixed multinomial logit.
Institute of Public Health, University of Southern Denmark, Denmark. dgh@dsi.dk
Dorte
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Gyrd-Hansen
Trine
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Kjaer
D000293:Adolescent; D000328:Adult; D003362:Cost-Benefit Analysis; D003718:Denmark; D005382:Financing, Personal / Q000706:statistics & numerical data*; D017048:Health Care Costs; D006801:Humans; D007407:Interviews as Topic; D008875:Middle Aged; D017059:Models, Econometric; D057240:Patient Preference / Q000191:economics* / Q000706:statistics & numerical data*; D019057:Quality-Adjusted Life Years; D012044:Regression Analysis; D011795:Surveys and Questionnaires; D055815:Young Adult