Referee Bias in Professional Soccer: Evidence from Colombia

This paper measures the magnitude of referee bias using data from the Colombian professional soccer league. Our dataset contains more than 1,600 observations encompassing all first-division games played between 2005 and 2010. We use both OLS and Poisson regressions to estimate the effect of the score difference on the length of injury time added at the end of both the first and second halves of each game. Our main result is that there is statistically-significant referee bias favoring home teams. In particular, we find that referees extend injury time by approximately a quarter of a minute if the home team is trailing the half or the game by one goal. We also find that referees tend to end injury time half a minute earlier if the home team is winning by one goal. Our estimation controls for various determinants of injury time such as the number of player substitutions, the number of yellow and red cards, the occurrence of penalties or other unusual events during the game. We also consider fixed effects at the team and referee levels. We study how the size of the referee bias might depend on variables such as attendance, ranking difference, previous performance in the tournament, homicide rates in the city of the home team, as well as a measure of historical performance of each team. Our results are consistent with the hypotheses that social pressure or psychological motives, either conscious or unconscious, exert a significant influence on referees’ decisions.