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Monday, August 30, 2010

Distance Matters - Travel and HFA

In recent posts, I've shown that crowd size doesn't matter in home field advantage, and I've traveled around college football conferences to show that the teams with the large, historic stadiums are not the ones that enjoy the best home field advantage. In fact, the award for best home field advantage in the country probably goes to Texas Tech's Jones Stadium. Arizona St. got +10 points in the Pac-10 playing at home versus on the road, and Indiana got +9 in the Big Ten.

But if crowd size doesn't matter, why do home teams tend to play better? One answer is travel. Distance makes the heart grow fonder, the legs weaker, the body dehydrated, the sleep patterns disrupted, the equipment misplaced or forgotten, the preparation time cut short, the players distracted, and the visiting teams loser. And I can prove it.

Using game results from 2006 to 2009, we can measure the effect of travel on performance. The first model below uses basic linear regression. We use three variables - DOffense, DDefense and Distance. DOffense and DDefense measure how good the road team's offense and defense are compared to the home team's. Distance is the distance traveled in thousands of miles.

The "Coef." for DOffense and DDefense are about 1. This makes sense. A team that is 1 point better than its opponent on offense or defense will win, on average, by 1 point. If it is 14 points better on offense and 28 points better on defense it will win, on average, by 42 points (28+14=42).

For every 1,000 miles a team travels, it loses 1.68 points. So, when Georgia Tech travels 600 miles to play Miami, it loses a point, but gains a point when the U comes calling. That might not seem like much, but about one out of every 13 games, or almost one game a season for the average team, is decided by 2 points or less - the price in points a team pays for traveling 600 miles instead of receiving a team from 600 miles away.

We then add the "_cons", or the home field advantage not explained by distance, and consider the average distance traveled for a game is about 500 miles, to get a net average home field advantage just under 1/2 a touchdown.

The logistic regression measures the effect of these variables on the probability that the road team will win. An "Odds Ratio" greater than 1 means that, as that variable increases, the odds of winning increase. If the Odds Ratio is less than 1, as that variable increases, the odds of winning decrease. Therefore, being 1 point better increases a team's odds by 1.13 and 1.15 for offense and defense, respectively. Traveling 1,000 miles decreases a team's odds of winning by more than a quarter (.694). So, for example, if Duke and North Carolina were evenly matched when UNC traveled to Duke (odds of UNC win = 1 to 2), the odds of a UNC victory drop to .818 to 2 if they had to travel 1,000 miles for that same game. In this scenario, 1 out or every 5 games is determined by travel.

What does this amount to? About 1 game in every 11 games has a different outcome because of where the game was played. 38% of that influence is a product of the distance that teams travel to play their road games. That, to me, is a pretty big deal.

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