Do ordering effects matter in willingness-to-pay studies of health care?

Willingness-to-pay studies are increasingly being used in the evaluation of health care programmes. However, there are methodological issues that need to be resolved before the potential of willingness-to-pay can be fully exploited as a tool for the economic evaluation of health care programmes. Of particular methodological interest are the consequences of varying the order in which willingness-to-pay questions are presented to respondents in contingent valuation studies. This paper examines the possibility of ordering effects in willingness-to-pay studies in health care. That is, when asking willingness-to-pay questions about three health care programmes within a single survey, does the order the programmes are presented have an impact on the reported willingness-to-pay? Ordering effects are observed in the ranking of the programmes, in the proportion of zero values reported and in the WTP for one of the programmes. The results suggest that the best explanation for the ordering effects is one of fading glow, whereby the first programme in any sequence captures much of the utility associated with giving.