May 9, 2006

Credulous Levitt gets nailed by an alert reader on his own blog

To support an ambitious argument that the importance of nature compared to nurture is overrated, economist Steven D. Levitt and writer Stephen J. Dubner started their New York Times "Freakonomics" column entitled "A Star Is Made" (i.e, "Made," not "Born") by claiming:

The Birth-Month Soccer Anomaly

If you were to examine the birth certificates of every soccer player in next month's World Cup tournament, you would most likely find a noteworthy quirk: elite soccer players are more likely to have been born in the earlier months of the year than in the later months.

They didn't offer any documentation for this, but Dubner later pointed to a study of the 1990 World Cup rosters. They then went on to claim:

If you then examined the European national youth teams that feed the World Cup and professional ranks, you would find this quirk to be even more pronounced. On recent English teams, for instance, half of the elite teenage soccer players were born in January, February or March, with the other half spread out over the remaining 9 months. In Germany, 52 elite youth players were born in the first three months of the year, with just 4 players born in the last three.

What might account for this anomaly? Here are a few guesses: a) certain astrological signs confer superior soccer skills; b) winter-born babies tend to have higher oxygen capacity, which increases soccer stamina; c) soccer-mad parents are more likely to conceive children in springtime, at the annual peak of soccer mania; d) none of the above.

Anders Ericsson, a 58-year-old psychology professor at Florida State University, says he believes strongly in "none of the above." He is the ringleader of what might be called the Expert Performance Movement, a loose coalition of scholars trying to answer an important and seemingly primordial question: When someone is very good at a given thing, what is it that actually makes him good?...

Their work, compiled in the "Cambridge Handbook of Expertise and Expert Performance," a 900-page academic book that will be published next month, makes a rather startling assertion: the trait we commonly call talent is highly overrated. Or, put another way, expert performers — whether in memory or surgery, ballet or computer programming — are nearly always made, not born. And yes, practice does make perfect. These may be the sort of clichés that parents are fond of whispering to their children. But these particular clichés just happen to be true...

If nothing else, the insights of Ericsson and his Expert Performance compatriots can explain the riddle of why so many elite soccer players are born early in the year.

Since youth sports are organized by age bracket, teams inevitably have a cutoff birth date. In the European youth soccer leagues, the cutoff date is Dec. 31. So when a coach is assessing two players in the same age bracket, one who happened to have been born in January and the other in December, the player born in January is likely to be bigger, stronger, more mature. Guess which player the coach is more likely to pick? He may be mistaking maturity for ability, but he is making his selection nonetheless. And once chosen, those January-born players are the ones who, year after year, receive the training, the deliberate practice and the feedback — to say nothing of the accompanying self-esteem — that will turn them into elites.

But, as so often with Dr. Levitt, the crucial question is: Is what he's saying really true in the first place?

It's not at all surprising or even terribly interesting that junior players in age-limited competition are more likely to be born on January 1 than on December 31 of any particular year. Those born earlier in the year are bigger and have more experience. Levitt and Dubner's attempt to draw vast inferences about nature versus nurture from this are laughable.

But it would be quite surprising if there was a sizable effect on the star professionals who play in the World Cup. Levitt's proposed mechanism turns out to be silly when you actually think about what world class athletes’ childhoods are like, you’d realize that, say, future NBA stars don’t waste all that much time hanging around on the basketball court humiliating other kids their own age. They spend much of their free time playing with kids, and even grown men, much older than themselves, because they are the only ones who can give them the level of competition they need to fulfill their potential.

Fortunately, on Levitt's own Freakonomics blog, Bill L. Lloyd has reviewed all the birthdates for recent World Cup soccer players he can find on Wikipedia. He's been working a lot harder on this question merely to post comments on a blog than Levitt and Dubner worked to write the most emailed article of the day in the Newspaper of Record. Here is Lloyd's summary:

My summaries show that from a sample group of 1,302 players in four World Cups (1982, 1986, 1998, 2006), 638 (49%) were born in the first half of the year, while 664 (51%) were born in the second half of the year.

Yet Levitt and Dubner wrote:

“If you were to examine the birth certificates of every soccer player in next month’s World Cup tournament, you would most likely find a noteworthy quirk: elite soccer players are more likely to have been born in the earlier months of the year than in the later months.”

The only evidence they can point to for this claim is that the 1990 World Cup ran 55%-45% in favor of [earlier-in-the-year] births.

Countering that, I noted that

- 1982 was 50%-50% [144 born in first half of year versus 144 born in second half]

- 1986 was 50%-50% [261 versus 261]

- 1998 was 47%-53% in favor of later year births [191-212],

- 2006 (with a small sample size) was [47%-53% or] 42-47 [out of 89 people on the four teams Lloyd looked at], again in favor of later-year births.

Dubner cites only the 1990 World Cup to back up their thesis [which was 55%-45%]. Levitt stands by Dubner’s citation in an e-mail to me, and says that he knows the hockey data best, and the data there is “quite robust”.

But he and Dubner didn’t write about hockey, they wrote about soccer. Two totally different sports might well have two totally different rates of birth month frequencies among pros.

I’ve pointed out to them repeatedly on this comment board that their thesis statement is incorrect, and they don’t seem one bit interested.

Everyone makes mistakes, but some people correct their mistakes. Levitt and Dubner, it appears, just hope they go away.

My published articles are archived at -- Steve Sailer

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