Australian soccer birthdays

In today's New York Times Freakonomics column, Levitt and Dubner uncover a startling fact:

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. 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.

And what accounts for this. They argue that subtle differences in youth soccer entry:

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.

Well that is an interesting theory but let's check out the Australian socceroos who likely have a different cut off date for youth entry. If you go to Football Federation Australia, there is a remarkable set of information on the socceroos (both the senior and junior teams). Now I only look at the senior team but here are the results by month (players born): Jan (3), Feb (4), Mar (5), Apr (0), May (4), June (1), July (3), Aug (9), Sept (3), Oct (6), Nov (1), Dec (5). Out of 44 in the squad, 12 (27%) are in Jan-Mar in contrast to the European result of 50%. In Australia, the same were born in the last three months as in the first three. The only distortion seems to arise with few players in Apr-June (5) and the most in Jul-Sept (15).

I haven't been able to find out the cut-off date for youth qualifying in Australia. However, if it follows season, it is a good bet that it is 30th June. In this case, the Australian experience appears to mirror the German one.

But there is another issue at work. Particularly when they are young, soccer players might move country. In particular, there would be lots of opportunities to shift hemispheres. So I wonder whether there is a reinforcement effect for birthdays through migration. That is, you work out that you don't stand a chance having a career in Europe if you are born in Oct-Dec and so move to Australia and South America (and vice versa for Apr-June). This seems to be an easily testable hypothesis. It may help us determine precisely when in their life great soccer players are made.