A statistical model for aggregating judgments by incorporating peer predictions

Abstract: We propose a probabilistic model to aggregate the answers of respondents answering multiple-choice questions. The model does not assume that everyone has access to the same information, and so does not assume that the consensus answer is correct. Instead, it infers the most probable world state, even if only a minority vote for it. Each respondent is modeled as receiving a signal contingent on the actual world state, and as using this signal to both determine their own answer and predict the answers given by others. By incorporating respondent's predictions of others' answers, the model infers latent parameters corresponding to the prior over world states and the probability of different signals being received in all possible world states, including counterfactual ones. Unlike other probabilistic models for aggregation, our model applies to both single and multiple questions, in which case it estimates each respondent's expertise. The model shows good performance, compared to a number of other probabilistic models, on data from seven studies covering different types of expertise.