Behind the Numbers: On the Issue of Home Cooking…Posted by KCarpenter on January 12th, 2011
Conference play has started and it is a glorious thing. While non-conference play has its charms (who doesn’t love to see heavyweights go at it?), conference play has a special allure. Games are exciting when there is history, and that’s what conferences offer: a history of rivalries and past meetings that add a little bit of spice to each new meeting. And while old wounds may ache, it’s the new ones that sting: The best part of conference play is the home-and-away series; to better understand the meaning of Duke and Ohio State’s close scrapes this past week, we need to understand home cooking.
“Home cooking.” When we talk basketball, we understand that this phrase is a euphemism for home-court advantage, a catch-all for the widely-discussed yet still mysterious phenomenon. Teams win more when they play on their home court. This is a fact. It’s the “why” that’s much more complicated, and there are many explanations. The “home cooking” euphemism itself is a partial explanation, metonymy for all the comforts of home: sleeping better in your own bed, being able to stick to your own routine, and, of course, literally getting to eat a home-cooked meal. Taken altogether, the psychological benefits of these things (coupled with the converse disadvantage of opponents lacking these things) is supposed to account for the edge that comes with playing at home. Of course, savvier or maybe just more cynical people hear “home cooking” and their minds turn to matters more sinister than mom’s meatloaf. “Home cooking” to these folks means referee bias in favor of the home team. The innocent and idealistic amongst us shudder at the thought, but the harsh reality is that referee bias is real.
Kyle Anderson and David Pierce in a 2009 article published in The Journal of Sports Sciences outline a series of systematic referee biases in men’s college basketball. In addition to being more likely to call fouls on the team with the lead and on the team with the fewest fouls, referees really do call more fouls on the visiting team. Also, oddly enough, these effects are more pronounced when the game is on national television. But, of course, home court advantage is bigger than just getting a few fouls going in favor of the home team, isn’t it?
Well, maybe. That’s the frustrating thing about home court advantage. Lots of folks have found real evidence of a home court advantage, but there are fewer coherent, definitive explanations of why the phenomenon exists. So, while Anderson and Pierce note that the visiting team gets 7% more fouls called against them, that only partially explains why David Harville and Michael Smith, writing in The American Statistician in 1994, found home court advantage to be worth 4.68 points (we can tsk-tsk about how they didn’t use a tempo-free measure later). In Barry Schwartz and Stephen Barsky’s broad look at home advantage across all sports (published in 1977 in Social Forces in a Durkheim-wielding article appropriately entitled “The Home Advantage”), the authors found significant advantages for the home team in attempted shots, made shots and rebounding. There are dozens of these studies, and while they don’t always find the same effect, they almost always find something real.
So there is an effect. Some of it can be accounted for by referee bias, but there is another part of home court advantage that’s harder to pin down. Maybe it really is because of a loud and active crowd, rowdy students and good old-fashioned intimidation. Maybe it really is literal home cooking and the psychological comforts of home. There have been efforts to put a finger on this by measuring levels of hormones in soccer players in home and away games, but nothing we can say definitively about basketball, though Lakers coach Phil Jackson seems to place some stock in the psychological disadvantage of playing away from home. Then again, his explanation largely seems to be based on the fact that players might be uncomfortable showing so much skin in revealing basketball uniforms, so you know, take his opinion on this with a grain of salt. Also from the grain of salt department, I would be remiss to not at least mention the “Different Kinds of Balls Theory of Home Court Advantage” courtesy of the New York Times college sports blog, which basically chalks up a chunk of home court advantage to the lack of total standardization of basketballs in the NCAA.
All of these things considered, we don’t need to know why home court advantage works, no matter how interesting the answer might turn out to be. The important thing is that we know that home court advantage is real, and, knowing that, we can use it to consider the results of home/away series and use that to make future predictions. And, if Ken Pomeroy and last season are accurate guides, we should be able to make some pretty good predictions. In a fascinating discussion of what he calls “The Head to Head Fallacy,” Pomeroy demonstrates the power of home court advantage using game data from last year’s set of home/away series. Most interestingly, the data shows that a team that wins at home against a given team is more likely to lose the rematch than win it! A team that wins by a single digit margin, as Duke won over Maryland and Ohio State won over Minnesota last weekend, for example, has only a 33.0% chance of winning the rematch. Even worse, a team that wins by a margin of only one or two points, like Arizona over California recently, has a mere 23.5% of winning the rematch. Conversely, teams that win on the road, as BYU won over UNLV last week, win the rematches 80.2% of the time. I don’t know if “home cooking” literally matters, but as far as the euphemism goes, it counts for a whole lot. Home court advantage isn’t an edge. Home court advantage is a giant, blood-dripping machete.