Comparing the effect of oath commitments and cheap talk entreaties in contingent valuation surveys: a randomised field experiment

Contingent valuation is a common methodology for eliciting preferences for non-market goods under hypothetical scenarios. Bias reduction strategies have been developed when evaluating low-cost realistic policy changes, including cheap-talk scripts, that alert respondents to tendencies to overstate values, and oath scripts, whereby respondents promise to answer valuation questions truthfully. This paper is the first large-scale experimental comparison of cheap-talk and oath commitments, amongst randomly-assigned respondents, in a field-setting using hypothetical voluntary donations. The data come from three general population surveys eliciting willingness to pay (WTP) for cultural institutions in England. We find limited and case-specific evidence regarding the effectiveness of cheap-talk and oath scripts in affecting stated values, which we attribute to realism and low cost of the proposals, which arguably diminishes hypothetical bias and produces realistic WTP values. We find evidence of the depressing effect of entreaty script on WTP or probability of paying in principle in only one of three case studies. Future research should replicate this experimental design with larger sample sizes and on non-voluntary payment mechanisms. Given the inconsistent findings across three large-scale experimental field studies, our recommendation is to include both cheap-talk and oath scripts where possible, and only cheap-talk where survey length is constrained.