A few weeks ago, I wrote an article on various explanations for home field advantage. One of the more interesting tidbits I learned was this:
Professional teams, however, seem to be better adjusted to life on the road. (The chartered planes and fancy hotels probably help.) A 1986 analysis of nearly 3,500 Premier League English professional soccer games found that the distance traveled had no effect on home-field advantage. A study in 1992 of professional baseball and hockey teams concluded that "travel factors" accounted for less than 1.5 percent of the variance in the home advantage. A notable exception is when teams travel from the Pacific time zone to the East Coast. In this situation, jet lag seems to impair performance. For instance, a 1995 study of MLB teams found that teams crossing the country scored, on average, 1.24 fewer runs than expected.
This year the home field advantage has been particularly potent for major league baseball, with road teams wracking up a combined record of 401-511. That's the lowest winning percentage for road teams (.421) since 1931. Of course, the season is young, and such statistical aberrations tend to vanish in the long run. Nevertheless, Jayson Stark recently quoted an anonymous GM on a possible reason for the road slump. And yes, it involves illicit substances:
"There's an 800-pound gorilla in every clubhouse, and it's greenies and steroids," one GM said. "The travel these days wears everyone out. Day games after night games. Coast-to-coast trips. How do you think these guys got through it before? Greenies have been in the game for probably 50 to 60 years. So now you take them away, and you don't think it takes a toll on teams when they're traveling?"
In a world in which these players change time zones as regularly as they change wrist bands, this is as logical a theory as we've heard. But why would it be showing up this year? Didn't baseball's ban on amphetamines actually take effect last year?
"Because I don't think guys were totally off greenies last year," the same GM said. "But this year, they've scared the living hell out of these guys. They know they're checking. They know the tests could come any time. They know Major League Baseball is trying to play gotcha. So what doctor wants to sign his name to this stuff now? Even if these guys want to use it now, where are they going to get it and who are they going to get it from?"
"Greenies," in case you don't know (and I need to google it, as I couldn't understand why baseball players would be eating a popular dog treat) are amphetamines.
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Whether or not long term use of amphetimines is improves performance could of course be open to debate I suppose. Surely they may be effective on occassional use but with long term use this would hurt ones ability to train and be in top physical condition? For example, the change in British footballers fitness levels was incredible after managers started cracking down on nights out and improving diets - drugs, be they alcohol or amphertamines are going to f*ck with performance over time.
But on to the stats, with which I am more familiar than the role of amphetamines in baseball. One season (or half a season) does not make any sort of trend. The most plausible answer based on the data here is surely that this is unusual, but not unexpected. There is clearly going to be a range across which the percentage of visiting wins is going to vary year on year (picture a normal distribution for the sake of argument). At some point, if you repeat the baseball season enough times, you are going to get seasons where that percentage is outside two SDs from the mean in eaither direction. On the results of one (or even two seasons) this is all I think could be said.
On home field advantage more generally, a paper by Jacklin publsihed in 2005 using results from Englsih football found that the home advantage has changed over time, notably in response to changing rewards - ie moving to three points for a win in football instead of two. So home advantage can be diminished if the right incentives are in place or if changes made for other reasons (like the changes in points awarded) have a knock-on effect elsewhere.
And I'm not at all sure that nine home wins in a row for a top team is an aberattion in basketball, play-offs or not. Didn't the Jazz go 19 games at home without losing this year? Still, I wonder how much advantage there is in a best-of seven series to the team that plays at home first. What is the percentage of series wins and how does this change with the realtive rankings of teams by seeding them? Has anyone ever done this analysis?
thats a very scary stat to look at it, hopefully it wont get an worse as the years go on