1. Bayesian Truth Serum (BTS) is a survey method that incentivizes truthful responses by having respondents provide their own answers to questions as well as estimates of what percentage of others would answer. 2. BTS scores responses based on how surprisingly common a respondent's answer is compared to their estimated distribution of others' answers. Answers that are more common than estimated receive higher scores, incentivizing truthful responses. 3. The premise of BTS is that individuals are generally best at estimating what beliefs and experiences are most common among others. By revealing discrepancies between personal responses and population estimates, BTS can identify untruthful responses.