Surveys that measure self-report are a workhorse in psychology and the social sciences, providing a vital window into beliefs, attitudes, and emotions, both at the level of groups and individuals. The validity of self-report data, however, is an enduring methodological concern, with self-reports vulnerable to a range of response biases, including (among others) the risk of social desirability bias in which, rather than responding honestly, participants answer questions in a way that they believe will be viewed favorably by others. One proposed solution to socially desirable responding is the so-called Bayesian Truth Serum (BTS), which aims to incentivize truthfulness by taking into account the relationship between an individual’s response and their belief about the dominant (or most likely) response given by other people and then assigning a high truthfulness score to answers that are surprisingly common (Prelec, 2004).

Although valid in theory (under a variety of assumptions), questions remain regarding the empirical utility of the BTS. One area of concern is participants’ uncertainty regarding incentives for truth-telling – if participants don’t understand the extent to which telling the truth is in their own interests (or they don’t believe that it matters) then the validity of the BTS is undermined. 

In the current study, Neville and Williams (2025) tested the role of clarifying incentives, particularly for addressing social desirability bias when answering sensitive questions. The authors administered an experimental survey design (N=877) including sensitive questions, curated from validated scales, that are relevant to current social attitudes and sensitivities (e.g., “Men are not particularly discriminated against”, “Younger people are usually more productive than older people at their jobs”). Three groups of participants completed the survey under different incentive conditions: the BTS delivered alone in a standard format, the BTS with an interim bonus payment that is awarded to participants (based on their BTS score) halfway through the survey to increase certainty in incentives, and a Regular Incentive control group in which participants receive payment without additional incentives.

The authors analyzed the effectiveness of the BTS through two registered hypotheses. First, the authors found that the BTS did not increase agreement with socially undesirable statements (compared to the control group), as theory would suggest, and even observed an opposite effect. This result, which could be confirmed by follow-up studies, raises some concerns about the robustness of the BTS method. Second, the authors conjectured that introducing an interim payment in the BTS mechanism would help reinforce its credibility in the eyes of the participants and would thus magnify its effect. However, the authors failed to detect a statistically significant difference between the standard BTS and interim-payment BTS mechanisms. Overall, the results of Neville and Williams (2025) call for some caution in the use of the BTS and for further work to better understand the contexts in which the BTS might be a useful tool to mitigate social desirability in surveys. 

This Stage 2 manuscript was evaluated over one round of in-depth review by two expert reviewers and a second round of review by the recommender. After the revisions, the recommender judged that the manuscript met the Stage 2 criteria and awarded a positive recommendation.