Home-field advantage is an important factor in almost every sport. In professional sports, home teams win a substantial fraction of their games. Home teams in Major League Baseball win at a 53.9 percent rate, in the National Football League at a 57.3 percent rate and in the National Basketball Assocation at a 60.5 percent rate. How do these numbers compare to the home-field advantage seen in Ivy League sports?
Home-field advantage is attributed to a number of different factors. Athletes might be more comfortable playing in front of their home fans; they might be better rested from sleeping in their own beds and not having to travel. Another potential factor is the influence of officiating, with referees possibly displaying implicit bias toward home teams. Some sports, such as baseball and softball, can also give home teams advantages, either by batting last or by introducing idiosyncrasies in various ballparks. Men’s sports typically have more fans than women’s sports, so there should be larger home-field advantages for men’s sports, if fans have a large impact.
Ivy League sports have far fewer fans than professional sports, which may reduce the magnitude of these home-field advantages. While Ivy League schools are all fairly close to each other, the traveling accommodations are much worse in the Ivy League than in professional sports. Therefore, it is not clear how significant the Ivy League home-field advantage is.
To explore the home-field advantages across different sports, I calculated the percentage of games that were won by the home team in conference games. These are plotted in the graphic. I used as many seasons as possible for each sport, which normally meant going back to the 2009–10 school year. I then tested for statistical significance for each sport against a null hypothesis of home teams winning 50 percent of games. The asterisks on top of the bars represent that those results are significant at the 0.05 level. I also tested for significant differences between each of the pairs of men’s and women’s sports. Interestingly, despite the differences in fan attendance and the actual home-field winning percentages in men’s and women’s sports, none of the pairs of sports showed significant differences. Note that in the graphic, ice hockey and soccer winning percentages exclude games that ended in ties.
The home-field advantages of baseball, men’s basketball and football in the Ivy League are all within the margin of error of the levels seen in the MLB, NBA and NFL. This is surprising, since so many external factors of the sports differ between the Ivy League and professional levels.
To investigate possible causes of home-field advantage in the Ancient Eight, I analyzed differences in free throws for the Yale basketball teams between home and away games. Free throws are a good way to isolate the impact of being at home on an individual player’s performance, since they are controlled plays with no defensive impact. If players perform better at home than away, it should show up in their free-throw percentages. Even though fans take particular effort to distract free-throw shooters, there is no direct, significant effect on actual performance. Since the start of the 2009–10 season, players in the Yale men’s program have hit 70 percent of free throws at home and 71 percent of free throws on the road. Players on the Eli women’s teams have hit 71 percent of their free throws at home and 69 percent of free throws on the road.
Neither of these differences, however, are statistically significant. This is very similar to Yale School of Management professor Tobias Moskowitz’s finding that NBA players hit 75.9 percent of their free throws both at home and away.
While success at the free-throw line is independent of location, there is evidence that the referees are more likely to call fouls in favor of the home team. Over the last seven seasons, the Yale men’s and women’s basketball teams have each attempted significantly more free throws at John J. Lee Amphitheater than at their opponents’ venues, as shown in the graph. This increase in free throws attempted by home teams was also seen in the NBA in Moskowitz’s analysis. Therefore, some of the home field advantage in the Ivy League is likely coming from officials being implicitly biased towards the home teams, or possibly because of the reactions of fans.
While it is not entirely clear what is causing the home-field advantage in Ivy League sports, both the numbers and the in-person experience suggest that the advantage does exist.
So the next time you attend a Yale home game, rest assured that your team possesses a subtle edge. Your presence might even influence the outcome.
Evan Green is a member of the Yale Undergraduate Sports Analytics Group. Contact the group at firstname.lastname@example.org .