Does Truth Pay? Investigating the Effectiveness of the Bayesian Truth Serum With an Interim Payment: A Registered Report

Self-report data are vital in psychological research, but biases such as careless responding and socially desirable responding can compromise their validity. Although various methods are employed to mitigate these biases, they have limitations. The Bayesian truth serum (BTS) offers a survey scoring method to incentivize truthfulness by leveraging correlations between personal and collective opinions and rewarding “surprisingly common” responses. In this study, we evaluated the effectiveness of the BTS in mitigating socially desirable responding to sensitive questions and tested whether an interim payment could enhance its efficacy by increasing trust. In a between-subjects experimental survey, 877 participants were randomly assigned to one of three conditions: BTS, BTS with interim payment, and regular incentive (RI). Contrary to the hypotheses, participants in the BTS conditions displayed lower agreement with socially undesirable statements compared with the RI condition. The interim payment did not significantly enhance the BTS’s effectiveness. Instead, response patterns diverged from the mechanism’s intended effects, raising concerns about its robustness. As the second registered report to challenge its efficacy, this study’s results cast serious doubt on the BTS as a reliable tool for mitigating socially desirable responding and improving the validity of self-report data in psychological research.