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

Self-report data is vital in psychological research, but biases like careless responding and socially desirable responding (SDR) can compromise its validity. While various methods are employed to mitigate these biases, they have limitations. The Bayesian Truth Serum (BTS; Prelec, 2004) offers a survey scoring method to incentivise truthfulness by leveraging correlations between personal and collective opinions and rewarding ‘surprisingly common’ responses. This study 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-subject experimental survey, 877 participants were randomly assigned to one of three conditions: BTS, BTS with Interim Payment (BTS+IP) and Regular Incentive (RI). Contrary to the hypotheses, participants in the BTS conditions displayed lower agreement with socially undesirable statements compared to 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 casts serious doubt on the BTS as a reliable tool for mitigating SDR and improving the validity of self-report data in psychological research.