Why are most players in European national youth football teams born in the first quarter of the year? And why does this continue in the later teams? Sports scientists have looked at the birth dates of all World Cup players - and have uncovered some interesting facts.
By Christina Steingröver
On 2 June, national coach Joachim Löw and his fellow coaches announced the final squad for the World Cup. For the team from the "Sport and Exercise" department at the Institute of Sport Science, this was an opportunity to research the birth dates of all the World Cup players. The aim of the data collection was to analyse the sample for a phenomenon that has been known for a long time: the so-called relative age effect.
This always occurs where reference dates are used to categorise age groups. The purpose of reference dates is to create equal conditions and thus equal opportunities in the respective groups. In sports selection teams, however, they often lead to a distorted distribution of birth dates. Using the example of a football team - cut-off date 1 January - this means that The date of birth of a conspicuous number of players falls at the beginning of the selection period.
Why do coaches often nominate older players? There are many reasons: a ten-year-old D-youth player born at the beginning of January is almost a year older than his team-mate born at the end of December. He therefore has ten per cent more life and development time as well as a greater wealth of experience. There is also a high probability that he is physically and cognitively more developed due to his earlier date of birth. Players born shortly after the cut-off date therefore have more time to acquire performance-defining characteristics, i.e. to grow, build up muscles and gain experience, before competing in sport.
These physical characteristics do not automatically lead to outstanding techniques. However, they do help older players to assert themselves or stand out against their younger team-mates and opponents. In selection procedures for district or national teams, for example, the technically advanced but not yet so well developed younger player is unable to show off his skills because his faster, bigger and stronger opponent does not give him the opportunity to do so.
Contrary to the original intention, deadlines do not create equal opportunities, but advantages for players with an early birthday. The whole thing continues: the older player is often praised and receives positive feedback due to his maturity-related performance advantage. Praise, successes, goals and trophies lead to a strong motivation to continue to improve and to train with commitment. If a relatively older player is nominated for a selection team against this background, the gap in the conditions under which the players train widens even further: selection players receive more training from often more qualified coaches under better conditions and can therefore better utilise their performance potential.
Now it would be expected that in adulthood - when all players have reached physical maturity - the age difference would no longer play a role. Accordingly, the same number of World Cup players should be born in each month and there should be no over-representation of the early months of the reference year. This means that around 61 of the 736 World Cup players should have been born in each month. In the more common scientific division into birth quarters, this means a number of 184 players per quarter. The actual birth date distribution of players in the five continental confederations (e.g. UEFA for Europe) suggests otherwise. While North and Central America show almost the expected equal distribution, South America shows an overrepresentation of players born in the first half of the selection year.
In the Asian confederation, it is clear to see that only a minority of players were born in the fourth quarter and are therefore among the relatively youngest. The UEFA teams are particularly susceptible to the relative age effect, with almost twice as many players born between January and March as between October and December. Despite its clarity, this result does not come as a great surprise, as the relative age effect has already been found in the vast majority of European national youth football teams. Of particular interest is the distribution of dates of birth in the African teams, where most of the players are relatively young.
Do the football systems there have certain mechanisms that do not favour the relatively older players? In the future, such mechanisms need to be researched - so that the German Football Association can ultimately also ensure that relatively younger players are not at a disadvantage because they were born later.
Christina Steingröver is a research assistant in the "Sport and Exercise" department at the Institute of Sport Science. The head of the department is Prof Dr Jörg Schorer.