Creating Truth-Telling Incentives with the Bayesian Truth Serum

The Bayesian truth serum (BTS) is a survey scoring method that creates truth-telling incentives for respondents answering multiple-choice questions about intrinsically private matters, such as opinions, tastes, and behavior. The authors test BTS in several studies, primarily using recognition questionnaires that present items such as brand names and scientific terms. One-third of the items were nonexistent foils. The BTS mechanism, which mathematically rewards "surprisingly common" answers, both rewarded truth telling, by heavily penalizing foil recognition, and induced truth telling, in that participants who were paid according to their BTS scores claimed to recognize fewer foils than control groups, even when given competing incentives to exaggerate. Survey takers who received BTS-based payments without explanation became less likely to recognize foils as they progressed through the survey, suggesting that they learned to respond to BTS incentives despite the absence of guidance. The mechanism also outperformed the solemn oath, a competing truth-inducement mechanism. Finally, when applied to judgments about contributing to a public good, BTS eliminated the bias common in contingent valuation elicitations.