understanding relative age effect in English football

Football, Data viz

Relative Age Effect (RAE) describes a phenomenon where a child who is born in the early part of a selection period gains a material advantage over a child born late in the selection period. The most common examples occur in academia and sport, where cohorts of children tend to be selected by establishing a somewhat arbitrary “cut-off” date (e.g. the UK school year starts in early September). Those born nearer to the cut-off date may demonstrate greater abilities than younger peers, simply because of this additional growth and development time. However, in practice this quirk can quickly entrench itself through all manner of biases – like greater attention from teachers, in academic settings – that only gets compounded over time as the performance gap is reinforced.

While we’re on the subject, there are many more systemic biases at play in such academic (and other) settings which often affect marginalised groups most severely and reinforce historic inequalities. For example, black students’ predicted A-level grades are the least accurate. RAE plays a part in influencing outcomes, but isn’t the only answer.

Relative age effect in sport was (probably) popularised by Malcom Gladwell’s Outliers, despite lots of pre-existing interest in the field itself. In the book, Gladwell stumbles across the case of elite Canadian hockey players, in which 40% of players were found to have been born in January, February, or March (with the cut-off for age competition in hockey at the start of the calendar year). I was curious about the incidence of this effect in English football a couple of years ago, and discovered something pretty similar:

This post got quite a lot of attention, which I think speaks to the fact that its quite a relatable story – everyone has a birthday, and many dreamed of making it as a pro. However, the visualisation itself hasn’t aged well (which I’ll leave for a future post). So, I thought I’d give this one a “remaster” of sorts:

Shouting out Tom Worville, as ever, for makeover inspiration 🍕