by Declan Jordan
One of the explanations for the persistence in relative age effects in sport is the physiological benefits that players born closer to the age cut-off for under-age competition (usually earlier in a calendar year) have over players born later in the period. At a young age this can mean up to almost a year in the development of players in the same age category. This physiological advantage may be compounded by the advantages of getting more game time and subsequently more coaching. This could mean some young players dropping out of the game, leading to a persistent age effect.
In football this physiological difference may be more beneficial in different positions. For example, goalkeepers tend to be taller than outfield players, and defenders also tend to be taller and bigger than midfielders and attackers (we can of course think of many midfielders and attackers that are tall and big).
The graphs below show the breakdown of quarter of birth for elite under-17 footballers - i.e. those representing their countries at FIFA U-17 World Cup Finals between 2007 and 2014. There are four tournaments each for male and female players over the period. The data comes from FIFA and player position is designated on the website for each tournament.
The figures show, from the flatter distribution of the female players, that relative age effects are far more pronounced for males than for females.
In football this physiological difference may be more beneficial in different positions. For example, goalkeepers tend to be taller than outfield players, and defenders also tend to be taller and bigger than midfielders and attackers (we can of course think of many midfielders and attackers that are tall and big).
The graphs below show the breakdown of quarter of birth for elite under-17 footballers - i.e. those representing their countries at FIFA U-17 World Cup Finals between 2007 and 2014. There are four tournaments each for male and female players over the period. The data comes from FIFA and player position is designated on the website for each tournament.
The figures show, from the flatter distribution of the female players, that relative age effects are far more pronounced for males than for females.
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However, within each cohort there is no difference in the relative age effect across different positions. This means that the proportion of players in each cohort born in each quarter of the calendar year is similar to proportions in each field position. This suggests that physiological differences at early stages of development may affect the likelihood of selection (and subsequent coaching attention) in every position. Unlike rugby, it seems there isn't a position for all body shapes in football. Perhaps an interesting question would be to look at relative age effects by position in a sport like rugby, where physical size matters for different positions.
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