The effects of extrinsic incentives on respondent behaviour in contingent valuation studies

In contingent valuation studies to assess the economic value of environmental goods, respondents are often given small presents or money amounts at the beginning of the interview to compensate them for their time spent on the survey and to encourage them to be conscientious when answering the questions. Yet, it is still an open question whether this practice biases contingent valuation survey responses, especially stated willingness to pay (WTP) for the respective environmental good. This study employs a set of field experiments to investigate the effect of respondent incentives in the form of monetary and in-kind gifts on responses in a contingent valuation survey. It is analysed how these different kinds of incentives affect (1) respondents' diligence when answering contingent valuation method questions, (2) the likelihood of a respondent to state a positive WTP and (3) the amount of stated WTP. Results show that with respect to raising respondents' diligence in the survey interview, a moderate monetary incentive is most effective. The results regarding the effect on WTP statements are less clear. While the likelihood to state a positive WTP is increased by most incentives, mean WTP estimates are virtually unaffected.