Are stars born or made? Here’s what World Cup 2006 has to say on the issue.

Last month we wrote a New York Times column asking whether superstars are born or whether they are made through a combination of the lots of practice, the right kind of practice, and coaching. The experts in the area suggest that superstars are made.

One conjecture we made in that column was that because the FIFA cutoff date for determining a child’s age for international play is January 1, we would expect that a disproportionate number of the players in the World Cup would be born in the early part of the year. The idea is that these kids will get special treatment and attention when they are teenagers because they will be developmentally almost a full year ahead of kids born in the latter part of the year. These developmental differences will fade away with age (i.e. by the time you are 25 it doesn’t matter much if you are 25 years and 1 month old or 24 years and two months old), but the early success, access to coaching, playing experience that the older kids got as teens would have long term effects on their soccer careers.

This conjecture led to some vigorous blog commenting (see here and here).

There were two nuances we missed though. First, the January 1 eligibility date wasn’t put into place by FIFA until 1997. And also, individual countries use different month cutoffs for determining who is eligible for different leagues within the country. Many countries use a date in the fall for their cutoffs, but there are a whole range of eligibility dates.

So, the clearest prediction we are left with concerning the World Cup is that if the FIFA January 1 cutoff matters and the experts in this area are correct, then for players born late enough to be affected by the 1997 date change should be disproportionately born in the early months of the year, and much less likely to be born in the last few months of the year. For players who are too old to be affected by the 1997 FIFA rule change (i.e. they were not teenagers at the time of the change), it is unclear what the pattern will be, but there is certainly no reason to expect a lot of January players. To really do these older players right, one would have to go country by country to determine what the cutoff rules were. (Something we haven’t done, but which I suppose some World Cup crazed blog readers will decide to do.)

We found a spreadsheet with the dates of birth of all players on World Cup rosters in 2006. What do the data say?

First, among players born in 1979 or later, making them 18 or younger when the FIFA January 1 cutoff took effect, the months of birth look like this:

January — 52
February — 43
March — 35
April — 38
May — 38
June — 25
July — 29
August — 31
September — 26
October — 35
November — 22
December –27

32.4 percent of the players were born in the first three months of the year, 25.2 percent of the players were born in months four through six, 21.5 percent in july to september, 21 percent in the last three months. Exactly what the theory predicts.

How about for the older World Cup players, those born before 1979? A very different pattern emerges:

January — 22
February — 23
March — 22
April — 23
May — 27
June — 31
July — 29
August — 36
September — 34
October — 27
November — 32
December –29

For the older players, only 20 percent of the older players were born January to March. 24 percent were born April-June. The months July-September were the most common.

All in all, this seems like pretty strong evidence in favor of the theory.

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  1. Leviathan says:

    1997 1979?

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  2. Leviathan says:

    1997 1979?

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  3. Harlan says:

    Interesting! That’s a pretty clear pattern. It reminds me of another phenomenon, which is handedness in several sports. In fencing, which I used to compete in, a much-greater-than-chance proportion of international-level fencers are left-handers. Now, anyone competing at that level is fully able to deal with left-handed fencers, and there’s not much reason to think that there’s any real advantage. (Unlike, say, baseball, where southpaw pitchers can throw curves that go the other way.) However, at the beginner levels, a left-handed fencer is a novelty to other fencers, and so the left-hander has a big early advantage in results. They may not be any better than their right-handed peers, but the handedness throws people off and they so get extra reinforcement early on and tend to stay in the sport longer. At least, that’s the theory.

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  4. Harlan says:

    Interesting! That’s a pretty clear pattern. It reminds me of another phenomenon, which is handedness in several sports. In fencing, which I used to compete in, a much-greater-than-chance proportion of international-level fencers are left-handers. Now, anyone competing at that level is fully able to deal with left-handed fencers, and there’s not much reason to think that there’s any real advantage. (Unlike, say, baseball, where southpaw pitchers can throw curves that go the other way.) However, at the beginner levels, a left-handed fencer is a novelty to other fencers, and so the left-hander has a big early advantage in results. They may not be any better than their right-handed peers, but the handedness throws people off and they so get extra reinforcement early on and tend to stay in the sport longer. At least, that’s the theory.

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  5. mjbigelow says:

    In the data, it’s clear that Jan and Feb are clear leaders but April and May both have more than Mar. It seems to dilute the effect to include those two months.

    Also, among the older generation (not born in 1979 or later), the opposite pattern emerges, with June through December having the largest counts. Could it be that because those born later in the year are somewhat younger than the rest of their cohort, they stay in the league longer? It seems like that would only affect somebody mid-year, not over time.

    Or is it just a coincidence?

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  6. mjbigelow says:

    In the data, it’s clear that Jan and Feb are clear leaders but April and May both have more than Mar. It seems to dilute the effect to include those two months.

    Also, among the older generation (not born in 1979 or later), the opposite pattern emerges, with June through December having the largest counts. Could it be that because those born later in the year are somewhat younger than the rest of their cohort, they stay in the league longer? It seems like that would only affect somebody mid-year, not over time.

    Or is it just a coincidence?

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  7. TartanBill says:

    Don’t dwell on individual months, the sample size is too small.

    Using all the data, a very simple calculation from the post 79 group yields
    y = -1.89x + 45.7 with R^2 = 0.63

    where X is the number of the month born in the year and Y is the number of players in that bin. That’s a pretty steep slope and a fairly high correlation. Although January looks like an outlier, removing it only modestly weakens the trend.

    For pre 79, the same analysis yields
    y = 0.96x + 21.7 with R^2 = 0.52. The slope is not as steep and the correlation more modest.

    In both cases, the trend is significant enough to lead one to believe there is an underlying cause. Of course alternative explanations exist. It may be that stars are unmade when the later birth month children lose interest and quit early.

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  8. TartanBill says:

    Don’t dwell on individual months, the sample size is too small.

    Using all the data, a very simple calculation from the post 79 group yields
    y = -1.89x + 45.7 with R^2 = 0.63

    where X is the number of the month born in the year and Y is the number of players in that bin. That’s a pretty steep slope and a fairly high correlation. Although January looks like an outlier, removing it only modestly weakens the trend.

    For pre 79, the same analysis yields
    y = 0.96x + 21.7 with R^2 = 0.52. The slope is not as steep and the correlation more modest.

    In both cases, the trend is significant enough to lead one to believe there is an underlying cause. Of course alternative explanations exist. It may be that stars are unmade when the later birth month children lose interest and quit early.

    Thumb up 0 Thumb down 0