Officiating bias, influenced by crowds, affects home field advantage

The roar of the crowd may subconsciously influence some referees to give an advantage to the home team, according to a study that examines the results of over 5,000 soccer matches in the English Premier League. The matches were played between 1992 and 2006, and involved 50 different referees, each of whom had officiated at least 25 games within that time period.

Ryan Boyko, a research assistant in the Department of Psychology in the Faculty of Arts and Sciences at Harvard University, led the study, which will be published in an upcoming edition of the Journal of Sports Sciences.

“Individual referees and the size of the crowd present are variables that affect the home field advantage. In order to ensure that all games are equally fair, ideally, all referees should be equally unaffected by the spectators,” says Boyko.

Boyko studied the number of goals scored by a team at home versus those scored while away, and found that teams scored 1.5 home goals on average, and 1.1 while away. Crowd size also had an impact on the number of goals scored by the home team, and for every additional 10,000 people in the crowd, the advantage for the home team increased by about 0.1 goals.

In addition to affecting the number of goals scored, the away team received more penalties, implying that referees are making calls in favor of the home team, possibly as a result of the influence of the crowd. Some individual referees are more susceptible to these influences than others. In fact, more experienced referees are less biased by the impact of a large audience, which suggests that they may develop a resistance to effects of the crowd.

Match results within the English Premier League were chosen for study because the games are heavily attended and the teams are located within the same time zone, eliminating long-distance travel as a factor involved with home field advantage. Information about the results of English Premier League games is also widely available online.

While previous research has studied the home advantage with regard to the influence of the crowd, player performance, and referees' decision-making processes, little work has been done on the variation of partiality from referee to referee. While understood to be present in sports that are both judged and scored, earlier studies had also shown that the home field advantage is more pronounced in sports that are subjectively judged, such as figure skating, as opposed to those that are objectively decided, such as speed skating, indicating a relationship between the judging process and the home field advantage.

The findings could suggest ways to increase the fairness of matches by identifying referee susceptibility to the external factors that are present at most sporting events.

“Referee training could include conditioning towards certain external factors, including crowd response,” Boyko says. “Leagues should be proactive about eliminating referee bias. The potential is there for a game to be altered because of factors that subconsciously affect the referee.”