Ambivalent statements in contingent valuation studies: inclusive response formats and giving respondents time to think

A recent concern in the valuation literature is the uncertainty respondents feel when posed with willingness-to-pay questions for environmental amenities in hypothetical market scenarios. Using a multiple-bounded discrete-choice format, the results indicate that respondents become less ambivalent when allowed considerable time to think about the valuation task before a response is elicited. In particular they tend to reduce the reported willingness to pay associated with low certainty of paying, hence resulting in more conservative welfare estimates. Implications for the application of environmental valuation techniques are discussed.