What causes the favourite-longshot bias? Further evidence from tennis

In sports betting markets, bets on favourites tend to have a higher expected value than bets on longshots. This article uses a data set of almost 45 000 professional single tennis matches to show that the favourite-longshot bias is much stronger in matches between lower-ranked players, in later-round matches and in high-profile tournaments. These results cannot be solely explained by bettors being locally risk-loving or overestimating chances of longshots, but are consistent with bookmakers protecting themselves against both better informed insiders and the general public exploiting new information.