The truth, the whole truth, and nothing but the truth—A multiple country test of an oath script

Hypothetical bias is one of the main issues bedeviling the field of nonmarket valuation. The general criticism is that survey responses reflect how people would like to behave, rather than how they actually behave. In our study of climate change and carbon emissions reductions, based on the increasing bulk of evidence from psychology and economics regarding the effects of making promises, we investigate the effect of an oath script in a contingent valuation survey. The survey was conducted in Sweden and China, and its results indicate that an oath script has significant effects on respondent behavior in answering willingness-to-pay (WTP) questions. In both countries, the shares of zero WTP responses and extremely high WTP responses decrease when an oath script is used, resulting in lower variance. Furthermore, the conditional WTP decreases in the Chinese but not in the Swedish sample. We also find that the effect of the oath script is not generally dependent on respondent characteristics, and the few differences we observe vary with the countries.