Eliciting patients' values by use of 'willingness to pay': letting the theory drive the method.

objectiveTo describe the three different ways in which 'willingness to pay' (WTP) has been used to elicit patients' values of alternative interventions.

designFor each of the three approaches a survey of patients or the public was undertaken. SETTING, PARTICIPANTS AND

interventionsstudied For two surveys, the setting was Aberdeen Maternity Hospital, where pregnant women were asked about their WTP for different methods of prenatal screening for cystic fibrosis. In the third survey, parents of primary and secondary schoolchildren were asked about their WTP for different ways of providing child health services.

main outcome measuresAbility of WTP to discriminate between options (i.e. to say whether one option is 'better' than another) and the consistency of WTP with stated preferences.

resultsExperience with some methods shows that, despite the apparent logic of the technique, it is difficult to elicit consistent responses whereby WTP values derived match the rankings of interventions compared. The most promising technique, the 'marginal approach', happens to conform more with economic theory than other approaches. Potential limitations of WTP, such as its association with ability to pay, are discussed, as are approaches to dealing with such problems. Finally, if patients prefer an intervention that is more costly than the status quo, logic dictates that those extra resources will have to be obtained from another health-care programme. In such contexts, to aid decision-making, values derived from members of the community for different programmes may be more relevant than values derived from patients. Initial studies in the use of WTP in this broader context of eliciting community values are also outlined.

conclusionsWTP has potential, but its application, and interpretation, are not straightforward. More testing of the 'marginal approach' is required and greater use of qualitative research, to assess the validity of the approach, should be made in this area.