Maybe the World Cup Wasn’t the Best Example

In our recent New York Times column, we talked about what makes people good at what they do.

As one example, we conjectured (based on some academic work done by others) that people born in the early months of the year would be overrepresented on World Cup rosters. The underlying theory is that in 1997, FIFA made January 1 the cutoff for determining ages in all international soccer competitions. If this rule had an important impact in determining who made the national youth soccer teams, then these early selection rules would play out to more long run success at the highest levels of soccer. The academic evidence is that these national teams are overwhelmingly made up of players born early in the calendar year, even on the age 21 and under teams, where a few months of physical development isn’t likely to make a big difference. A commenter on our blog, Bill Loyd, has done some hard work to gather data and argues that for past World Cups and for a few of the 2006 squads that he found, he doesn’t see the pattern we predict.

Why might this be the case? For the earlier World Cups, it might not be very surprising that no pattern is there because the FIFA rule didn’t come in until 1997. More fundamentally, the FIFA selection rules and the rules that different countries use for play within the county differ.

For instance, as many readers have emailed us, in the U.S., the age cutoffs tend to be in the summer. In Germany, the within country age cutoff is August 1. Thus, in soccer there are two different competitive pressures at work: one pushing towards more players born in the early months and the other towards more players in the later months. Much of the study of birth-date timing focuses on the cutoff rules within countries, virtually all of them finding important effects.

In light of this difference between FIFA and country rules, the example we gave of the World Cup might not have been the best one, even though the age effect is very strong in the national youth squads that feed many World Cup teams.

This shouldn’t distract from the important fact that the evidence in the literature overwhelming supports the basic point — that across many activities, you can identify long-term effects of essentially arbitrary age cutoffs early in life.

Perhaps a better example than the World Cup would have been the N.H.L. Here is one graph that I found on the web of the birth month of NHL hockey players versus Canadians and Americans more generally:

The black-and-white dots are the NHL players, who are much more likely to be born in January and February and much less likely to be born September-December. This is the sort of pattern that appears over and over in these sorts of studies.

Some other readers have offered a clever, very Freakonomics-y alternative explanation for these age patterns: the parents are lying about their child’s birthday. If the parents want the kid to be a star, they take an older kid and change his date of birth to make him eligible to play with younger children. While I don’t think this is actually the primary reason for what people find in these studies, is definitely worth thinking about.

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  1. Excuse me I thought that the first comment I made the machine lost it. That’s why I post the same two times.

    Alejandro

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  2. Excuse me I thought that the first comment I made the machine lost it. That’s why I post the same two times.

    Alejandro

    Thumb up 0 Thumb down 0
  3. beach says:

    zbicyclist,
    You may find this interesting this article, about the effect of surname initials on tenured economic professors, interesting:

    http://www.aeaweb.org/jep/contents/#9

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  4. beach says:

    zbicyclist,
    You may find this interesting this article, about the effect of surname initials on tenured economic professors, interesting:

    http://www.aeaweb.org/jep/contents/#9

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  5. prosa says:

    “Say what you will about Barry Bonds and steroids, but his home run production jumped from upper tier to Ruthian after spending a very considerable (almost pathological) amount of time in the weight room.”

    Excessive weight training frequently leads to a condition called “overtraining,” in which people actually begin to lose strength and size. It can be especially pronounced with someone Bonds’ age. And it should come as no surprise that use of steroids helps lessen the risk of overtraining.

    Thumb up 0 Thumb down 0
  6. prosa says:

    “Say what you will about Barry Bonds and steroids, but his home run production jumped from upper tier to Ruthian after spending a very considerable (almost pathological) amount of time in the weight room.”

    Excessive weight training frequently leads to a condition called “overtraining,” in which people actually begin to lose strength and size. It can be especially pronounced with someone Bonds’ age. And it should come as no surprise that use of steroids helps lessen the risk of overtraining.

    Thumb up 0 Thumb down 0
  7. zbicyclist says:

    Not sure anyone’s posted on this effect before, but certain mental illnesses are associated with particular birth months.(notably schizophrenia, peaking among those born from December through May)

    December through May overlap substantially with the hockey player peak months.

    Source: http://www.neoteny.org/a/birthmonth.html

    In terms of causal factors mentioned in these notes, they seem to pay no attention to cutoff dates — instead they pay attention to the seasonal variation in hormones (e.g. in the mother) due to factors such as the amount of daylight affecting the pineal gland.

    A quote: “The pineal gland, activated in the dark months, tends to suppress gonadal hormonal production. When it is suppressed, during periods of long days, sex hormones rise. We have already alluded to Badian’s (1983) report of a higher rate of nonrighthandedness in males conceived from December through May ”

    There are two alternative hypotheses, at least, wandering around here. If lefthanders are more common in December-May births, and if there is some advantage to being lefthanded in hockey (are NHL players closer to 50-50 Righhand-Lefthand than the general population is?) this could be part of the effect.

    The second hypothesis is concerned with hormones themselves. Might certain hormonal conditions in utero create the type of personality more likely to succeed as a hockey player? Seems possible.

    I’m out of my depth going much further with this research.

    On a net basis, there seems to be a paucity of evidence (largely NHL hockey players) and a variety of alternative hypotheses for the effect trumpeted in the Freakonomics article.

    Thumb up 0 Thumb down 0
  8. zbicyclist says:

    Not sure anyone’s posted on this effect before, but certain mental illnesses are associated with particular birth months.(notably schizophrenia, peaking among those born from December through May)

    December through May overlap substantially with the hockey player peak months.

    Source: http://www.neoteny.org/a/birthmonth.html

    In terms of causal factors mentioned in these notes, they seem to pay no attention to cutoff dates — instead they pay attention to the seasonal variation in hormones (e.g. in the mother) due to factors such as the amount of daylight affecting the pineal gland.

    A quote: “The pineal gland, activated in the dark months, tends to suppress gonadal hormonal production. When it is suppressed, during periods of long days, sex hormones rise. We have already alluded to Badian’s (1983) report of a higher rate of nonrighthandedness in males conceived from December through May ”

    There are two alternative hypotheses, at least, wandering around here. If lefthanders are more common in December-May births, and if there is some advantage to being lefthanded in hockey (are NHL players closer to 50-50 Righhand-Lefthand than the general population is?) this could be part of the effect.

    The second hypothesis is concerned with hormones themselves. Might certain hormonal conditions in utero create the type of personality more likely to succeed as a hockey player? Seems possible.

    I’m out of my depth going much further with this research.

    On a net basis, there seems to be a paucity of evidence (largely NHL hockey players) and a variety of alternative hypotheses for the effect trumpeted in the Freakonomics article.

    Thumb up 0 Thumb down 0