Monday, August 30, 2010

Wrigley: the Worst Home-Field Advantage in Baseball

I love Wrigley Field. I do. It's one of my favorite places in the world. I say that to inform you that nothing in this post is out of spite for the venue I revere as a mecca of the baseball world. And as much as I give Cubs fans a hard time, I don't really think they're worse than the fans of any other team. There are some great Cubs fans and some abominable ones just as any fan base is prone to including members from both ends of the spectrum of tolerability.

But the home-field advantage at Wrigley, for the last several decades, has been the worst in all of baseball, and I've got the numbers to prove it.

I started out investigating home-field advantage in general in the hopes of proving something about the significance of psychology in baseball. The first wave of research showed that as far back as I could look (1901) there always has been a home-field advantage league-wide. In every season of Major League Baseball, the home teams have, collectively, registered a winning record. There have been 4 seasons in which the teams of either the National League or the American League had a collective losing record at home, but it has never happened across baseball.

Then I came across this study of the 2004 Major League Baseball season that went to great lengths to isolate the effect of both home-field advantage and travel on the probability of winning. I was happy to learn that travel was ruled to have no significant effect on win probability for either team and that home-field advantage is very real. However, the study also concluded that home-field advantage was statistically significant only in games decided by one run—but in those one-run games, it's pretty significant.

I checked using the play index tool to see if those conclusions held true throughout history. They did . . . kind of. In the nearly 88,000 games played since 1970, home teams have a .540 winning percentage. Obviously that's significant. But in all the games decided by just one run over the past 40 years, the home team's winning percentage is even higher: .608. I still think there's an advantage in the other games, too, because a .511 winning percentage in games decided by 2 or more runs is nothing to sneeze at (and .518 in games decided by 3 or more runs), but I can't ignore the huge difference home-field makes in one-run games.

So I decided to compare the winning percentages of all the teams across baseball over that time period. (I chose 1970 because I wanted to keep things fairly modern but include a large enough sample to make it significant.) I limited the results just to one-run games, since that's the condition in which home-field advantage is supposed to be at its most pronounced. What I found is that the Friendly Confines are a little too friendly to the visiting teams.

I don't really have a reaction other than . . . Crap. Is it Wrigley? Is it us? I don't know. But it's not working.

UPDATE: Okay, now I do have a reaction. Could the problem be day baseball?
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