Talent ID

Remove the relative age effect by changing players’ shirt numbers

The relative age effect is widespread across many sports. It refers to the consistent findings whereby junior sport teams (typically representative teams) are populated by players born earlier in the year, or soon after the cut-off date for a particular sport. In other words, coaches and selectors more often than not select older players to play in the best teams.

Why does this matter?

Well, imagine this scenario. A girl born in January is 11 months older than a competitor. Consequently, she is bigger and stronger, and dominates her age group. She gets a scholarship into an academy and is provided with the best coaching services available. Unbeknown to everyone, her competitor, the girl 11 months her junior, actually possesses the same level of skill. But due to the fact she is younger, she is less developed physically, and cannot dominate her age group during the younger years. As a result, she is overlooked for a scholarship.

Removing the relative age effect should therefore be a priority for sports authorities.

A novel strategy to remove the relative age effect

David Mann and Pleun van Ginneken tested three methods to reduce the relative age effect in junior soccer. Talent scouts were divided into three groups that varied in the information that they were provided about the soccer players who they watched:

  1. Provided with NO information about the players age
  2. Provided with the players’ age
  3. Provided with knowledge that the players shirt number corresponded to their relative age (i.e., number 1 = oldest player)


  • The relative age effect was present regardless of whether the talent scout was told the player’s age (i.e., Groups 1 and 2 above).
  • The relative age effect was eliminated when talent scouts were made aware that the players’ shirt number corresponded with their relative age (i.e., Group 3 above).

Concluding message

Manipulating player’s shirt numbers so that oldest players wear the lowest numbers is an effective strategy to make coaches and talent scouts aware of players’ age. Indeed, simply telling a scout the age of a player was not enough to remove the relative age effect.


Mann, D. L., & van Ginneken, P. J. (2016). Age-ordered shirt numbering reduces the selection bias associated with the relative age effect. Journal of sports sciences, 1-7.


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