Tennis Home Court – Research Notes
I’ve built out my men’s tennis results database quite a bit in the last couple of months, so I thought I’d revisit my research into home court advantage.
To recall, I started with ATP main draw matches from 2009. I focused on the subset of matches where the tournament was in the home country of one player, but not the other. I excluded matches where either player was a wild card entry–that usually applies to the home player. I did so because I think there is a separate “wild card” effect that reflects selection bias. (Tourney organizers choose players who did not make the cut but whose chances, for whatever reason, are better than their ranking would suggest.)
As I reported in my initial research, using about 450 matches from the 2009 main draw dataset, the home player won 17% more matches than expected. (“Expected” winnings are derived from my bare-bones algorithm to predict the winner of the match.) Using ranking points, this is roughly equivalent to giving the home player credit for 50% more ranking points than he actually has.
For example, Lleyton Hewitt is currently ranked 54th, with 870 ranking points. If we make this adjustment for the Australian Open, we’d say he’ll play at a level equal to someone with 1,305 ranking points, which would be 32nd in the world. Instead of giving him a 36% chance of winning his first round match against David Nalbandian, the home-court-adjusted number would give him a 47% chance. In this case the results might bear us out: The match went to 9-7 in the fifth set.
The surprise came when I expanded the dataset to include Challenger main draw matches and ATP-level qualifier matches. In 2009 Challengers, home players only won 6% more often than expected–equivalent to a ranking points multiplier of 1.15. In 2009 ATP qualies, the home court advantage was only 2%–a multiplier of about 1.05. Whatever confers the home court advantage in ATP main draw matches may not apply at all levels.
I next looked at the same datasets for 2010. Here are the home court advantages (and ranking points multipliers) observed last year:
- ATP main draw: 12% (1.35)
- Challenger main draw: 4% (1.1)
- ATP qualifiers: 14% (1.3)
The first two numbers don’t differ much from the ’09 observations, but the qualifier numbers come out of nowhere.
Until I’m able to look at more matches from before 2009, I hesitate to draw any conclusions about the qualifiers. That still leaves us with a fairly consistent gap between the home court advantage observed at the ATP main draw and Challenger main draw levels.
To the extent that crowd involvement plays a part, it seems reasonable to expect that players would get a bigger boost on a bigger stage. Even on outer courts in the early rounds, fans tend to pull for the locals. At challengers, the atmosphere is often more like a club tournament where the audience is next to nonexistent.
Another major possibility is that some combination of selection bias and the inadequacy of my prediction algorithm accounts for the lack of observed home court advantage in challengers. Players have more choice of where to play at the lower levels, so they will tend to stay closer to home. It may mean that, even exclusive of wild cards, the distribution of home-country players and non-home-country players is different; perhaps the bottom ends of challenger draws are disproportionately packed with home-country players. This is something that I can investigate further.
UPDATE: Just ran the numbers for 2008. The ATP main draw home court advantage remained consistent, at a 16% boost for the home player. The ATP qualifier pool also showed the same home court advantage. However, 2008 differed from later years in that in Challenger main draw matches, home players got an 11% boost, much bigger than in 2009 or 2010.