European Under-21 Championships: Relative Age Effect

The relative age effect is a widely-acknowledged phenomenon in sport; whereby participants born soon after an age cut-off date are disproportionately represented compared to those born nearly 12 months later.

To what extent does this effect exist in the European Under-21 Championships, and what are some of the implications?

The cut-off for the Championships is on 1^st January, 23 and a half years before the competition*. The theory argues that players born in December are less likely to be picked, having been left behind by their older, stronger peers.

This is somewhat borne out in the data, though there appears to be an effect through the academic year cut-off, which is 1^st September in most European countries. 

This is also true if we look only at major nations (England, France, Germany, Italy, Netherlands, Portugal and Spain).

However, an implication of the relative age effect that is overlooked in Malcolm Gladwell’s Outliers is that those ‘disadvantaged’ by the relative age effect benefit hugely from playing with older players (first pointed out to me by James Grayson in two ice hockey articles – one and two).

If December/summer children can compete with their peers despite the age disadvantage, their performance potential is likely to be higher. This is shown by the number of senior international appearances made by Euro Under-21 squad members born in the summer; particularly noticeable among the major nations.

The key question is how robust this is over a larger sample. Notable summer children in this sample include Zinedine Zidane, Raul, Patrick Vieira, Miroslav Klose, Lukas Podolski, Daniele de Rossi, Dirk Kuyt and Frank Lampard; all these players have more than 90 caps. Is this to do with the relative age effect, or just a freak example of enormously talented summer children?

Perhaps a more obvious example of age effects is through the comparison of players with noticeable age differences, in years. Taking players who were 21 or older on 1^st June in the year of the tournament, and comparing them to players younger than 21 (22% of all players), it’s clear that the younger group far exceed the achievements of their peers. Over 1 in 4 of these under-21s won more than 40 senior caps, compared to about 1 in 7 for the older group.

This is hardly surprising; if you’re a teenager who is able to compete with players 2-5 years older than you, it’s likely you’ll do well. There is also the additional effect of some of the very best 21-23 year olds already being capped at senior level, and no longer being part of the junior teams.

The practical implications of all this – particularly around the single-year relative age effect – are up for debate, and comments are welcome below.

*The tournament is denoted as ‘under-21s’, but includes players who were 21 or younger during the qualification period, and therefore may be as old as 23 during the tournament.