Does Belief Heterogeneity Explain Asset Prices: The Case of the Longshot Bias

This article studies belief heterogeneity in a benchmark competitive asset market: a market for Arrow–Debreu securities. We show that differences in agents' beliefs lead to a systematic pricing pattern, the favourite–longshot bias (FLB): securities with a low-pay-out probability are overpriced, whereas securities with high probability pay-out are underpriced. We apply demand estimation techniques to betting market data, and find that the observed FLB is explained by a two-type population consisting of canonical traders, who hold virtually correct beliefs and are the majority type in the population (70%); and noise traders exhibiting significant belief dispersion. Furthermore, exploiting variation in public information across markets in our data set, we show that our belief heterogeneity model empirically outperforms existing preference-based explanations of the FLB.