Relative age effect

The IOC,[10] FIFA[11] and the six international football confederations (AFC, CAF, CONCACAF, CONMEBOL, OFC and UEFA[12]) all use 1 January as their administrative cut-off which is most commonly used but, 1 September is used in the UK,[5] like many other locations around the world.

The second graph, by the month, shows the birth distribution of over 4,000 players involved in the qualifying squads for U17, U19 and U21 tournaments organised by UEFA in 2010–11.

This declining distribution from the beginning of the year for professional athlete participation has been seen in sports like: association football,[14] baseball,[15] cricket,[16] gymnastics,[17] handball,[18] ice hockey,[19] rugby league,[20] running,[21] skiing,[22] swimming,[17] tennis,[23] and the Youth Olympic Games,[24] as well as non-physical sports like shooting.

[citation needed] Relative age effects are caused by birthdate eligibility rules but can be affected by parents, coaches and athletes through other mechanisms.

[50] Playing position, federation membership, and individual and team performance also contribute to the effect,[18] with older players having a higher risk of injury.

[62] Bio-banding can help promote appropriate training loads and reduce injury risk,[63] while increasing technical demands from players,[64] however, sports already categorized by maturation metrics like Judo,[65] may not see those effects.

More longitudinal studies are needed,[66] alongside more reliable ways to band individuals,[67] as biological, psychological and social development doesn't progress in synchrony,[68] creating different imbalances in the groups.

The third graph illustrates the relative age effect in graduations from the University of Oxford over a 10-year period, which has also been seen in UK Nobel laureates.

[76] However, like in sport, the effect diminishes over time after middle school,[77] and those born later in the year perform better in university education.