Four elicitation methods are compared in a split-sample, contingent-valuation study valuing avoidance of episodes of ill health linked to air pollution: two discrete methods and two more-continuous methods. Respondents to a traditional payment card (PC) question gave willingness-to-pay values that were lower than those implied by dichotomous-choice (DC) responses. However, followup questions
... [Show full abstract] showed that DC respondents were less certain of their stated behavior than were PC respondents. When respondents were told to be ``almost certain’ ’ of their responses, responses to the DC and the PC formats converged.