Comparing willingness-to-pay: bidding game format versus open-ended and payment scale formats.

The willingness-to-pay technique is being used increasingly in the economic evaluation of new health care technologies. Clinical trials of two methods of screening for colorectal cancer are currently being conducted in the UK and willingness-to-pay for screening has already been estimated by means of a questionnaire survey, using open-ended (OE) and payment scale (PS) formats. This paper addresses the same medical issue, although it elicits willingness-to-pay values by means of a bidding game in an interview setting. Interviews were conducted with 106 subjects in Nottingham. The bidding game format produced considerably higher valuations than had either of the previous questionnaire formats, whilst the significant differences between agreed valuations obtained using different initial bids supported the existence of starting-point bias in the bidding game. As with the questionnaire study, the majority of interview subjects offered relative valuations of tests at variance with their expressed preferences over the same tests. Given the significant difference in valuations generated by different formats, it follows that the economic case for preferring any one technology over others will depend considerably upon whichever format happens to have been used to generate the valuations.