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The home-field advantage is something most people take for granted. Not James Curley. He's an assistant professor of psychology at Columbia University. He's put the notion to the test by compiling results of 200,000 matches from the entire 127 year history of English professional football.
Curley demonstrated that home home-field advantage does, in fact, exist. He joined Bill Littlefield.
BL: Do any of the theories about why home-field advantage has often been born out seem especially convincing?
JC: Well, there are lots of theories, and I think most of them might be true in different parts of the world in different leagues. The main theories are probably to do with the hostile nature of playing away from home. So crowds are very partisan, and officials may become influenced by home crowds. Another major theory is that it's difficult for road teams or away teams to travel to certain places. They get tired. They're not as comfortable.
And another theory put forward by some economists in England is that home players might actually put more effort in because they're being monitored more by the home team and by the home crowd. So there's actually a little bit of data that suggests that that one might be true.
BL: Now I understand that having done this enormous job of looking at these 200,000 games, you still weren't satisfied. And where did you look next for data?
JC: Anywhere that plays soccer, basically, I'll take the data. I think there's some really, really interesting outliers with home-field advantage. So the Nigerian Premier League is probably the strongest outlier. It's really, really, really difficult to lose a home game in the Nigerian Premier League. The reasons that have been put forward by the league and Nigerian journalists are that the referees are very much influenced by the home teams. Actually the way in which the referees get paid is kind of a reimbursement by the home teams. And also some of these games are played in the very, very remote parts of the northeast of the country, and the television companies won't even go and film the games. So players have always said that there's always a lot of home-field advantage going on which is unfair advantage.
BL: Yeah, this is a kind of home-field advantage which goes well beyond cutting the grass to the length that your players prefer and that sort of thing, obviously.
JC: For sure. It's not the only place where it happens either. Guatemala also has a very, very high home win percent. As leagues go on over time, the home-field advantage actually tends to come down. So as professionalism progresses, the home-field advantage does diminish. And that's been seen in nearly all soccer leagues. It's been seen in the NBA. MLS does have a home-field advantage, and it's stronger than the major European leagues, but even that seems to be diminishing.
What seems to be true is that teams that play at altitude appear to have a stronger home-field advantage. So Real Salt Lake and Colorado tend to do a little bit better at home and, in soccer more generally, it's well known in South American World Cup qualifying that if you play at Lapaz in Bolivia, even if you're Brazil or Argentina, you'll do well to even get a draw in that game.
BL: You've talked about outliers in terms of regions. What about outliers in terms of particular sports?
JC: Knowing soccer most strongly, I think soccer does have a slightly higher home-field advantage compared to the other sports. It's a little bit harder to compare because there's the draw in soccer, which you just don't get in North American sports, and so away teams are actually satisfied with a draw, and it's a mentality issue. They will actually take the draw.
I think in baseball and hockey, the home-field advantage exists. It's stable, but it's diminished. It's not as high, so it's around 55 percent win rate, and it's quite stable. Basketball still has a slightly higher home-field advantage, but that's coming down. And there's a few arguments that that might be again to do with the way in which officials become influenced calling a foul in the last minute, kind of thing.
BL: And as you've explained, in soccer officials tend to be a little more likely to call a foul next to the goal and give the home team the advantage rather than the other way around. Likewise red cards and yellow cards.
JC: Definitely. It's known, for instance, in the EPL that penalty kicks, 66 percent on average since '92, have been awarded to the home team. It used to be as high as 75 percent. Now it's around about 55 percent. If you ask the referees, they're obviously going to say, "No, I was not influenced by the home crowd." And it's hard to know whether it's because the home team carries the play more and therefore more likely to get the call. But it does seem that there are certain ways in which referees do influence games.
BL: Wouldn't it be refreshing if you were to hear a referee actually say, "By Gosh, I was influenced. You should have heard what those people were shouting at me."
JC: I used to referee junior soccer and I was influenced by the parents of 11 year olds, so I'd imagine when I've got two parents shouting at me compared to 80,000 shouting at me, I'm sure that there's some subconscious bias going on even if it's not a conscious bias.
BL: Is there anything that the general manager of a pro sports team can take away from your research that might help him or her doing the job?
JC: There is a home-field advantage, but I don't think visiting teams should be suckered into thinking that a draw is good enough. And I think that's probably the take-home message: that they should know it exists, but feel as if it's very overcomable.
This story was produced as part of Only A Game’s “Celebration of Home.”
This segment aired on November 28, 2015.