Saturday, June 21, 2008

Do teams play worse after a time zone change? Part II

(UPDATE: This post was updated after I discovered my own analysis had three teams in the wrong time zones.)

In the previous post, I discussed an MLB-funded study on jet lag, ""Measuring Circadian Advantage in Major League Baseball: A 10-Year Retrospective Study," by W. Christopher Winter.

It claimed to find that teams recently changing time zones performed worse than expected. Conventional wisdom in sleep science is that, for each time zone crossed, it takes one day to adapt. So a team that flew from Tampa to Oakland two days ago should be at a "2-day disadvantage" in their circadian rhythm. The study looked at all MLB games where the two teams were not equally adapted to their time zone, and claimed to have found that the disadvantaged teams did in fact play worse.

While I couldn't find the actual study,
the data quoted in a press release actually supports the opposite conclusion: that jet lag has no effect. It appears that the study didn’t correct for home field advantage, and jet-lagged teams tended to be road teams. So what the researcher thought was jet lag was really just the normal road team effect.

To double-check, I ran the numbers myself. I was able to substantially reproduce the numbers in the press release.

I'll start with the records of teams with the "circadian advantage" (less jet-lagged than the opposition). All numbers, by the way, are 1998-2007. (This represents only about 20% of all games, because, in most games, the teams are equally jet-lagged.)

All teams less jet-lagged than opposition

2621-2425 (.519) – study
2537-2337 (.520) – me

The numbers are very slightly different, and I'm not sure why.

Now, here are home teams that had the jet-lag advantage:

Home teams less jet-lagged than opposition

2002-1679 (.544) – study
1930-1609 (.545) – me

Again, I'm not sure why the study has so many more games than I do. It could be my 2:00am programming was wrong; it could be I assumed the wrong time zone for certain teams (Arizona is on Pacific time, right?); it could be the press release got a number wrong. Regardless, I think the results are close enough that I did the same analysis the study did.

Here are home teams that had a jet-lag DISadvantage:

Home teams more jet-lagged than opposition

746-619 (.547) – study
728-607 (.545) – me

Both the original study, and my study, contradict the press release and the press reports: having a "circadian advantage" does NOT improve your chances of winning. In fact, the original study shows such teams did very slightly *worse* than normal, not better.

Of course, this doesn't adjust for the quality of teams. But over 10 years, you'd think it would all even out.

Full year-by-year data is available on request.

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At Saturday, June 21, 2008 5:54:00 PM, Blogger Phil Birnbaum said...

I reran the numbers for the 70s and 80s.

70s: home team has jet lag advantage: .521. Home team has disadvantage: .524.

80s: home team has advantage: .552. Home team has disadvantage: .545.

At Saturday, June 21, 2008 8:36:00 PM, Anonymous Anonymous said...

I'd be happy to send you the abstract. Your figures are right. Slight circadian advantage has little effect on game outcome. It's the 2 and especially 3 hour games that tend to show changes.

At Sunday, June 22, 2008 12:25:00 AM, Blogger Phil Birnbaum said...

Hi, Dr. Winter,

Sure, I'd love to have the abstract. Looking forward to seeing the results.


At Monday, June 23, 2008 12:44:00 PM, Anonymous Anonymous said...

Point of clarification:

If the home team just got back from a road trip, wouldn't they also be suffering the same Time Zone Effects?

At Monday, June 23, 2008 1:57:00 PM, Blogger Matty D said...

One of the more compelling points in the paper (via your original post) was the increase in winning percentage on the second day (47%) v. the first (40%). I don't imagine that there are enough 1 game series to make this a home/away team affect. Did you see the same difference, Phil? Is this not statistically significant?

At Monday, June 23, 2008 3:16:00 PM, Blogger Phil Birnbaum said...

>"If the home team just got back from a road trip, wouldn't they also be suffering the same Time Zone Effects?"

Yes. Those are the games where the home team has the disadvantage -- when they recently got back from another time zone and the visiting team did not.

At Monday, June 23, 2008 3:20:00 PM, Blogger Phil Birnbaum said...


In 160 games, the SD of winning percentage is about 40 points. So the difference between two 160-game samples would be root 2 times that, or about 60 points.

That means the difference of 70 points is not statistically significant.

At Tuesday, June 24, 2008 12:00:00 PM, Anonymous Anonymous said...


Arizona is technically on Mountain Time, but Arizona also doesn't observe Daylight Savings Time, so for pretty much the full baseball season, Phoenix is effectively on Pacific (Daylight) Time.

At Tuesday, June 24, 2008 12:07:00 PM, Blogger Phil Birnbaum said...

Thanks, David!


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