What the evidence does show, however, is that referees favour home teams in judgment calls, particularly those that happen at a crucial stage in a game. The authors focus on decisions that are less susceptible to influence by player pressure, but give some discretion to the official. If a batter chooses not to swing at a baseball pitch, the pitch is more likely to be called a strike if the home team is pitching. This tendency is most extreme in close games. In soccer, referees are more likely to award penalties to the home team, hand out fewer punishments for offences to home players, and adjust the amount of overtime played depending on whether the home team is losing (more overtime is given) or winning (less). Sir Alex is unlikely to dwell on this last point: the extra minutes that Manchester United get at home when they are trailing is known as “Fergie time”.


Are referees deliberately biased? The authors think not. Instead, they blame the fact that referees, like the rest of us, tend subconsciously to rely on crowdsourcing, picking up on the mood of the crowd when making their decision. “Anchoring” is the name economists give to people’s tendency to be unduly influenced by outside suggestion. Take away the crowd and the home bias shrinks, as it did a few years back when 21 Italian soccer matches were played without supporters following incidents of crowd violence. In these games the home bias declined by 23% on fouls called, by 26% for yellow cards and by a remarkable 70% for red cards, which remove a player from the game and have a particularly big impact on the result. This bias is consistently higher in soccer than in most other sports because there are many more judgments for the referee to make. If technology is ever adopted to help referees—using TV to review contentious calls, for instance—away teams should benefit most.

http://www.economist.com/node/18330455?story_id=18330455