Implicit versus explicit ranking: on inferring ordinal preferences for health care programmes based on differences in willingness-to-pay.

The paper explores the merit of the willingness-to-pay (WTP) method as a way to elicit public preferences regarding health care priorities. The aim is to test the extent to which the implicit ranking inferred from the ordinal differences in WTP-values corresponds with respondents' explicit ranking of the same programmes. This issue of convergent validity is explored by face-to-face interviewing of population samples in six European countries-in total 1240 respondents. The most consistent result is the inconsistency of WTP and explicit ranking in all six countries. The convergent validity of WTP is low, particularly among those who did not state different WTP-values on the three programmes being considered.