Tuesday, August 9, 2011

Home Field Advantage and the Value of Away Draws in the Premier League: The 2010/11 Season

I've previously written about home field advantage in football. While there's no shortage of debate about the actual source of the home field advantage by learned and and not so learned minds alike, the facts are straightforward: home field advantage is a statistical fact. Across the big leagues of European football, more matches end with the home team winning than end with any other outcome (away win or draw). The numbers vary slightly across leagues, with around 45-48% of matches resulting in a home win and the remainder roughly evenly split between wins for the away team and draws.

The statistical fact of the home field advantage suggests that one key to a successful season is to capitalize on home field advantage and to neutralize another team's potential home field advantage as much as possible when playing away. A quick look at match data for the 2010/11 season allows us to get a handle on which teams have enjoyed the most and least amount of home field advantage and which have been best able to neutralize it.

Before we look at the numbers for individual teams, here's first the overall proportion of home and away wins in the Premier League for last season. Home teams won 47% of the time; away teams won 24% of the time; and the remainder ended in draws. Clearly, last season was no exception to the general rule that the home team wins about as often as it does not, and winning about twice as often as the away team.

But we can assume that not all teams were equally adept at turning home field advantage into wins. As it turns out, there was huge variation across clubs in the league when it came to taking advantage of home field advantage.

While some teams like Wigan, West Ham, and Blackpool managed to win only 1 in 4 (26%) of their home matches, eventual champions Manchester United won 95% of theirs, as the next graph shows. United clearly stood out on this dimension, as a full 13 teams won fewer than half of their home matches.

So, clearly, one critical component of United's championship run was making Old Trafford a fortress other clubs just couldn't take. The next best teams in terms of producing wins at home were Chelsea, Manchester City, Liverpool, and Arsenal at percentages well below Manchester United's.

So if winning at home was one key ingredient for United's success, what about neutralizing other clubs' potential home field advantage? To see which clubs did particularly well on this score, I calculated (and then graphed) the proportions of home and away fixtures won. The home fixtures portion of this graph (lower panel) simply reproduces the first graph and is provided for orientation. The top panel shows the proportion of away fixtures teams managed to win.

You may be surprised to hear this: but as it turns out, Manchester United won matches away from home as frequently as Blackpool did. Of course, the Tangerines' problem was that they won as much (or as little) away as they did at home - about 1 in 4 matches. In fact, Manchester United found itself in the middle of the pack, winning as many away matches as Blackpool, Sunderland, Newcastle, and Liverpool. In contrast, Chelsea, Tottenham, Arsenal and Manchester City all outdid the champions, winning a significantly higher proportion of their away fixtures. Another way to think about their records is to say that these clubs were best able to neutralize their opponents' home field advantage (as measured in wins, that is).

So how did United do it if they didn't do it by winning on the road? Turns out, they did it by (a) winning lots more matches at home than on the road, and (b) when on the road, they managed a draw more than half the time. They were the kings of drawing on the road, while its closest competitors either won or lost when playing away from home.

Whether this season will be similar is anyone's guess, but it's clear that winning at home and not losing on the road did it for the Red Devils last year.