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

I realized I made a mistake in my last two posts on the time-zone study … I had three of the teams in the wrong time zone. The updated results still aren't signficant, but I'm going to go back and correct the numbers in the previous two posts.

I found this out because Dr. Winter, the study's author, was kind enough to send his own results for comparison. These are the home team's record with various amounts of "circadian advantage". (The circadian advantage occurs when one team has less time-zone lag than another, where the lag is the number of time zones crossed, minus the number of days since the crossing. So if you flew from Seattle to Chicago two days ago, you have a disadvantage of 1 – you crossed 2 time zones, but had 1 day to recover.)

Here are Dr. Winter's numbers:

Home record/3-hour circadian advantage: 77-48 (.616)
Home record/2-hour circadian advantage: 487-426 (.533)
Home record/1-hour circadian advantage: 1438-1204 (.544)
Home record/0 circadian advantage: 10207-8872 (0.535)
Home record/1-hour circadian disadvantage: 577-465 (.554)
Home record/2-hour circadian disadvantage: 152-133 (.533)
Home record/3-hour circadian disadvantage: 15-20 (.429)

The only sign that there's some effect is in the 3-day case. Home teams that just got back from the other coast went only .429; when the *visiting* team just arrived from the other coast, the home team beat them up to the tune of .616. However, neither of those two results is statistically significant – both are between 1 and 2 standard deviations from the mean.

My numbers are still a bit different from Dr. Winter's, but not much different – the conclusions are the same. And Dr. Winter did say that these numbers were adjusted since the original study and analysis is continuing.

For the record, here are the time zones I used (Retrosheet abbreviations):

3 hours from east: LAA, OAK, SFN, LAN, SDN, SEA, ARI, ANA
2 hours: COL
1 hour: CHA, CHN, MIL, TEX, HOU, MIN, KCA, SLN
0 hours: all others

I'm now going to go back and update the other two posts with the correct numbers.

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

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

In the last two posts, I reviewed reports of Dr. W. Christopher Winter's study on jet lag and baseball performance. The data suggested that the observed effect was just home field advantage.

In a comment to the second post, Dr. Winter said that most of the effect came from 2- and 3-hour time changes. So I reran the numbers, and considered only the first game where one team had 3-hour jet lag (from the day before), and the other team had none.

1997-2006 home winning percentage
----------------------------------
Home team jet-lagged: 14-19 (.424)
Road team jet-lagged: 72-46 (.610)

There's actually something here, although it's not statistically significant with the small sample of games.

Here are the breakdowns by decade:


2000-2007 home winning percentage
----------------------------------
Home team jet-lagged: 6-16 (.273)
Road team jet-lagged: 68-43 (.613)


1990-1999 home winning percentage
----------------------------------
Home team jet-lagged: 20-17 (.541)
Road team jet-lagged: 68-45 (.602)


1980-1989 home winning percentage
----------------------------------
Home team jet-lagged: 11-15 (.423)
Road team jet-lagged: 43-43 (.500)


1970-1979 home winning percentage
----------------------------------
Home team jet-lagged: 14-9 (.609)
Road team jet-lagged: 47-48 (.495)


None of these results looks statistically significant. The overall totals are:

1970-2007 home winning percentage
-----------------------------------
Home team jet-lagged: 51-57 (.472)
Road team jet-lagged: 226-179 (.558)

The effect goes in the right direction, but neither result is significantly different from .530. The difference between the two numbers is 86 points; that's about 1.5 SD from zero, which again is not statistically significant.

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.

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.