This paper examines the influence of objectively irrelevant information on prediction accuracy in horse-racing betting exchange markets. In horse racing, the name of a horse does not depend on the horse's performance and is thus uninformative. We investigate the impact of fast-sounding horse names on prediction market price accuracy and betting returns. Using over 3 million horse bets, we find evidence that the winning probabilities of bets on horses with fast-sounding names are overstated, which impairs the prediction accuracy of such bets. This finding implies that the prices in betting exchange markets are not efficient, as prices become distorted by incorporating the misleading information from a horse's fast-sounding name. This bias translates into significantly lower betting returns for horses classified as fastsounding compared to the returns of all other horses.
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