The contingent valuation method in health care.

The contingent valuation method (CVM) is a survey-based, hypothetical and direct method to determine monetary valuations of effects of health technologies. This comprehensive review of CVM in the health care literature points at methodological as well as conceptual issues of CVM and on willingness to pay as a measure of benefits compared with other measures used in medical technology assessment. Studies published before 1998 were found by searching computerised databases and former review literature. Studies were included, when performing CVM using original data and meeting qualitative criteria. Theoretical validity of CVM was sufficiently shown and there were several indications of convergent validity. No results on criterion validity and only a few on reliability were found. There was widespread use of different elicitation formats, which make comparisons of studies problematic. Direct questions were seen problematic. First bids used in bidding games influenced the monetary valuation significantly (starting point bias). There were indications that the range of bids of payment cards also affected the valuation (range bias). However, no strategic bias was found. The influence of different states of valuation (ex-ante, ex-post) and of payment methods, as well as the possible aggregation of the results of decomposed scenarios rather than more complex holistic scenarios, were rarely investigated. Further methodological analysis and testing seems to be necessary before CVM may be used in health care decision making. Important research topics are the connection of assessment of different elicitation methods and criterion validity as well as tests on reliability according to methodological issues. Concerning conceptual issues, the analysis of the influence of different states of evaluation and of the status of the respondents as diseased or non-diseased, as well as the aggregation of results of decomposed scenarios, proved to be topics of further research.