Eliciting Willingness to Pay: Comparing Closed-Ended with Open-Ended and Payment Scale Formats

Willingness to pay (WTP) is increasingly being used as amea-sure of valuation in health technology assessment. A variety of formats for eliciting values are available, although the rela-tive virtues of each remain the subject ofmethodological con-troversy. This article compares valuation results obtained us-ing a WTP survey instrument in a closed-ended format with those obtained from instruments using open-ended and pay-ment scale formats. Samples of subjects were drawn from a general population, and all were asked to value the same in-tervention—alternative methods of screening for colorectal cancer. It was discovered that, whereas the open-ended and payment scale formats produced broadly similar valuations, the closed-ended format produced significantly higher WTP valuations and different justifications for those valuations. It is hypothesized that anchoring and yea-saying effects ex