Thursday, June 19, 2008

Do teams play worse after a time zone change?

According to a resent research presentation by a Baltimore sleep scientist, baseball teams that have recently travelled across time zones play worse than otherwise.

It's called "Measuring Circadian Advantage in Major League Baseball: A 10-Year Retrospective Study," by W. Christopher Winter, M.D. It was funded by MLB.

The study was presented at a conference on June 10, but I can't find it online. (That drives me nuts -- the study is quoted by a whole bunch of press releases, the author is quoted directly, but the actual paper isn't publicly available? What's with that?)

The Scientific American writeup quotes the results this way: if a team travels three time zones west (like from New York to San Francisco), its chance of winning would be

-- 40% on the first day
-- 47% on the second day
-- 48% on the third day
-- 50% on the fourth day

That, I assume, doesn't include home field advantage.

The article does imply, near the end, that the first game of three-time-zone trip happened only 160 times in the 10 years of the study. That's a 64-96 record for the tripping team. That works out to about 2.5 SDs away from .500, which is statistically significant. But it depends on the study having controlled for the quality of the teams and home field advantage.

I have a vague feeling that I've seen studies that checked the time-zone theory of home field advantage, and couldn't find any effect. But I'm not sure. In any case, when the study becomes available, I'll take a look at it.

(Hat tip: Freakonomics)

UPDATE: This article has more details, and it seems like the data doesn't support the conclusion. Here's the summary:

Approximately 79.1 percent of the games analyzed (19,084 of 24,133 games) were played between teams at equal circadian times. The remaining 5,046 games featured teams with different circadian times. In these games, the team with the circadian advantage won 2,621 games (51.9 percent). However, 3,681 of these 5,046 games were also played with a home field advantage. In isolating games in which the away team held the circadian advantage (1,365 games), the away team won 619 games (45.3 percent).

From this, we can figure that:

When the road team had the "circadian advantage" -- meaning the home team had to travel more time zones to get to the game -- the disadvantaged home team's winning percentage was 54.7% (746-619), almost exactly the normal home field advantage.

When the home team had the circadian advantage, they were 2002-1679, for 54.4% -- again almost exactly the normal home field advantage, and almost exactly the same HFA they had when the other team had the circadian advantage!
In bold:

Home teams were .544 with circadian advantage;
Home teams were .547 with circadian disadvantage.

So, basically, the study's data show that time zone travel doesn't matter at all. The apparent difference is completely caused by the fact that teams that have recently travelled are more likely to be road teams.

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