Reliability and validity of the contingent valuation method for estimating willingness to pay

Abstract

BACKGROUND:
The contingent valuation (CV) method is an alternative approach to typical health economic methods for valuing interventions that have both health and non-health outcomes. Fertility treatment, such as in vitro fertilisation (IVF), fall into this category because of the significant non-health outcomes associated with having children.

AIM:
To estimate the general population's willingness to pay (WTP) for one cycle of IVF and one year of IVF treatment, and to test the reliability and validity of a CV instrument.

METHODS:
Three online CV surveys were administered to a total of 1870 participants from the Australian general population using an ex-post perspective, that is, they assumed they were infertile and needed IVF to conceive a child. Participants answered questions with starting point WTP bids of 2018 Australian dollars (AU$) 4000 or $10,000 for the cost of one IVF cycle, and treatment success rates of 10%, 20% and 50% per IVF cycle. Tests for reliability, internal construct validity, starting point bias, and external validity were performed.

RESULTS:
Depending on the success rate and the starting point WTP bid, the mean WTP for one IVF cycle ranged from $6135 to $13,561, while the mean WTP for one year of IVF treatment varied from $17,080 to $31,006. The CV method was reliable and satisfied internal construct and external criterion validity. However strong starting point bias was evident, rendering the mean WTP values highly imprecise.

CONCLUSION:
The CV method holds promise for eliciting the value of interventions, such as fertility treatment, that have significant health and non-health outcomes. Survey instruments that prevent starting point bias are essential. Comparing the results of CV methods to other value elicitation methods is needed to confirm convergent validity.