The impact of the design of payment scales on the willingness to pay for health gains.

The questionnaire format applied in a CV study represents the way in which the WTP estimates are obtained. Payment scales are often used in CV studies as the questionnaire format of choice. The study summarized here analyzes the impact of the design of two payment scales (PS) on the monetary value of QALY gains. The scales differed in terms of their end-points, mid points, and coarseness. We judged the performance of the two PS against several indicators: the average WTP per QALY estimates, post-estimation uncertainty levels, the existence of mid-point concentration, and the dependency on end-points. Our results show that PS design influences respondents' WTP values. The results also suggest that a more detailed scale with a more realistic range may help respondents to elicit values closer to their "true" WTP values, hence produce higher-quality outcomes. Further research and pretesting strategies are suggested to explore and minimize the effects of PS design on WTP estimates, which may ultimately increase the quality of WTP estimates.