Research on sports betting often identifies biased evaluation by bookmakers and

corresponding opportunities for profitable strategies to bettors. Such studies

repeatedly provide evidence for the existence of biased betting odds for different

periods and leagues, leaving the impression that inefficiencies are very common.

Since most studies cover only a few seasons, the question remains whether these

market inefficiencies persist over time. We review the literature on the big five

leagues in European association football and then analyse 14 seasons to detect

the occurrence and duration of betting market inefficiencies. While our results

replicate the temporal findings of previous research, they also show that biases do

not persist systematically over time and across leagues. Furthermore, a Monte

Carlo simulation reveals that the number of inefficient periods barely exceeds

what would be expected in an efficient market.