Heterogeneous Beliefs and Prediction Market Accuracy

Résumé

We consider a prediction market in which traders have heterogeneous prior beliefs in probabilities. In the two-state case, we derive necessary and sufficient conditions so that the prediction market is accurate in the sense that the equilibrium state price equals the mean probabilities of traders' beliefs. We also provide a necessary and sufficient condition for the well documented favorite-longshot bias. In an extension to many states, we revisit the results of Varian (1985) on the relationship between equilibrium state price and belief heterogeneity.