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What Stats Tell Us About How Much Being The Home Team Matters In Sports

MARY LOUISE KELLY, HOST:

You've heard the phrase home sweet home, right? Well, so far in this year's World Series, it has been more like home sweet doom. The team on the road has so far won every game. The Houston Astros won all three games they played in D.C. And the Washington Nationals - go Nats - have won every game in Houston. Now this is the first time this has happened in the playoffs, and not just for Major League Baseball. It hasn't happened in a seven-game series in pro basketball or hockey either.

So what's going on here? Well, Michael Lopez is director of data and analytics at the National Football League. He is also a statistics lecturer at Skidmore College. And he has been crunching some numbers on this. Hi, there.

MICHAEL LOPEZ: Hi. Thanks so much for having me on.

KELLY: What is a home-field advantage? I mean, just explain why this would help a team win in the first place. What are the factors that go into that?

LOPEZ: Sure. So the home advantage is a combination of a couple of things. One, it's travel. Two, it's rest. And three, certainly it's the case in several sports that there could be an impact of the home advantage on referee decisions. And so when you mix all that together, there's some benefit of playing at home. But the exact way that works obviously depends on each of the sports.

KELLY: All right, and when we apply this to baseball, how much of an advantage does playing at home confer?

LOPEZ: So in baseball, it's about a 4% edge relative to, say, a 50/50 game. If you took two teams that were relatively evenly matched, paired them up at where one of the teams was a home team, that home team is going to win about 54% of the time. And if you were to contrast that to other sports, say, like the NBA, you could take two NBA teams that were roughly the same in terms of talent, put one of them at home, and that home team is going to win about 62% of the time.

KELLY: Wow.

LOPEZ: So in all, that ends up being about three times the benefit to being the home team in the NBA relative to in Major League Baseball.

KELLY: And you're basing this on crunching statistics over the - what? - last several years?

LOPEZ: Sure, this is over the last 15 years or so of looking at data. Specifically, we're looking at the betting odds in terms of who the betting odds perceive as the likely winner.

KELLY: And what would explain this? Why would playing at home matter more when you're playing basketball than playing baseball?

LOPEZ: Well, certainly in basketball, the fans are right on top of the court. And you can imagine that they're going to have a little bit of influence, whether that's influence over the opposing team, influence over the officials or just general support for the home team when things aren't going as well. In baseball, there's a little bit - you have fans who are further set back. And then I think the other funny thing about baseball is that when fans are cheering to support their team, if their pitcher is up in a big spot, they're standing and clapping. If their batter's up in a big spot, they're standing and clapping. And so regardless, they're actually kind of doing the same thing. And so maybe that their behavior and their overall influence on the game is a little bit harder to sort of come through.

KELLY: All right, so let's turn you to tonight, the decisive game seven. It's going to be played in Houston. Should - if we were putting bets on this, should we put our money on the Nats?

LOPEZ: (Laughter) Well, that depends on who you want to root for. The game is pretty close to...

KELLY: We'll put our money on the Nats. No, I'm sorry. Go ahead.

LOPEZ: (Laughter) The game is pretty close to a 50/50. Sort of - if you look at the betting odds, it's pretty close to a 50/50 game. The Astros are given a slight bump, but that - perhaps that's obviously in part because they're the home team. So they're getting that 4% edge, the sort of 54/46 outcome. And part of that is because they're playing at home.

KELLY: Setting aside home-field advantage, is there a momentum advantage? If you've won the last game, the last two games, three games, does that help?

LOPEZ: Teasing out momentum in a sport that is as random as baseball - and when I say as random, the teams are so close in terms of talent, so it's not all that surprising when the worst team in baseball would beat the best team. Teasing out momentum from other factors that also influence game outcomes is particularly hard. Certainly that - you would maybe think that the Nats walk in with a little bit of momentum tonight. They're comfortable on the road. But relative to all else, I think it will come down to what actually happens on the field.

KELLY: I think you're telling me absolutely anything could happen tonight.

LOPEZ: (Laughter) Well, I think that's playoff baseball.

KELLY: That is sports statistician Michael Lopez joining us by Skype. Thanks so much.

LOPEZ: Thanks for having me on, Mary Louise.

(SOUNDBITE OF SPORTS SONG, "YOU ARE THE RIGHT ONE") Transcript provided by NPR, Copyright NPR.