Eliciting willingness to pay in obstetrics: comparing a direct and an indirect valuation method for complex health outcomes

Abstract

To compare direct and indirect willingness to pay (WTP) elicitation methods in terms of feasibility, reliability, and comparability. The application is obstetrics, where always both a mother's and a child's health are at stake. An open-ended contingent valuation method (CVM) as a direct WTP elicitation method, and the discrete choice experiment (DCE) as an indirect WTP elicitation method. Vignettes to be valued were based on clinical patient data. Participants were 88 laypersons who received their questionnaires by postal mail. The DCE task was completed faster (p=0.006) and was regarded easier (p<0.001) than the CVM task. Test-retest for CVM was substantial (ICC=0.76), and for DCE moderate (k=0.49). Female sex (p<0.001), age≥50 years (p=0.013), higher income (p<0.001), and higher education (p<0.001) were associated with higher WTP. Correlation between CVM and DCE was 0.79 (Kendall's Tau-b; p<0.001). The implied WTP as derived with DCE was between 2.3 and 10.2 times higher than with CVM. The relationship between the WTPs was linear. It is yet unclear what lies behind the numbers of DCE. DCE has no methodological benefits over the conventional CVM when eliciting WTP for complex health outcomes in obstetrics.