Willingness to pay: A valid and reliable measure of health state preference

The development of methods to measure willingness to pay (WTP) has renewed interest in cost-benefit analysis (CBA) for the economic evaluation of health care programs. The authors studied the construct validity and test-retest reliability of WTP as a measure of health state preferences in a survey of 102 persons (mean age 62 years; 54 % male) who had chronic lung disease (forced expiratory volume <70%). Interview measurements in-cluded self-reported symptoms, the oxygen-cost diagram for dyspnea, Short-Form 36 for general health status, rating scale and standard gamble for value and utility of current health state relative to death and healthy lung functioning, and WTP for a hypothetical intervention offering a 99 % chance of healthy lung functioning and a 1 % chance of death. WTP was elicited by a simple bidding game. To test for starting-point bias, the respondents were randomly assigned to one of five starting bids. All health status and preference measurements except WTP (controlling for income) showed significant (p < 0.05) differences between disease-severity groups (mild/moderate/severe). WTP was significantly (p = 0.01) associ-ated with household income, but other health status and preference measures were not. The measure most highly correlated with WTP was standard gamble (r =-0.46). Ther