New light on the longshot bias

Abstract

The longshot bias is the tendency for bettors to put more money on horses with long odds than is justified by their objective probability of winning: thus favourites win more often than projected by their odds. This challenges normative assumptions as it means the return increases with the probability of winning. Even though the longshot bias is well-known, it has defied authoritative explanation. This article draws on studies of the longshot bias over 50 years across four continents to show that its nature is consistent with two bettor populations. One is risk-averse, knowledgeable about winners, backs favourites, believes in the gambler's fallacy, and has a positive expected return. The other, a larger group is risk loving, backs longshots, believes in hot hands, and has a significant, negative expected return. The crossover between the two groups occurs where the probability of a positive result is about 0.2. This matches the transition from risk aversion to risk embrace which has been found in a variety of behavioural studies.