Does don't know mean no? Analysis of 'don't know' responses in dichotomous choice contingent valuation questions

The 'don't know' response option in contingent valuation dichotomous choice questions is analysed using data from both willingness to pay and willingness to accept studies. An empirical analysis is conducted to determine whether respondents are stating a response similar to yes or no responses or a middle response. It is found that don't know responses are similar to no responses in the willingness to pay study. In the willingness to accept study, it is found that the `don't know' responses are similar to a middle response. It is further suggested that researchers consider calculating ambivalence bounds when a don't know response is a middle response.