#Research brief

A longitudinal investigation into the relative age effect in an English professional club

Dr Adam Kelly, 16 Mar 2023


Dr Adam Kelly, co-author of the paper 'A longitudinal investigation into the relative age effect in an English professional club', presents the research project and its implications.

The nuanced age differences within the traditional age brackets we use to structure our youth systems can disadvantage younger players within a team. The relative age effect (RAE) is the term used to describe the difficulties younger players within a given age bracket may face.

There is already an established body of research drawing attention to the RAE. There is also a growing number of studies highlighting the benefits a young player can reap from playing competitively with older players, bringing an alternative angle to the RAE discussion. Adam's paper is situated right at the heart of this debate, providing insightful research on the RAE and the potential benefits of playing competitively with older players.

Key take-aways

  • Once a young player has been identified and brought to an academy, there are positive reverse effects that come with being the youngest player within an age group.

  • However, far fewer players feel the benefits of positive reverse effects than the number of players who find themselves at a disadvantage due to conventional relative age effects in talent identification.

  • Those working in the game should consider relative age effects when thinking about how they identify talented youth players.

Watch brief

Part 1: Relative age effects and the underdog hypothesis
Part 2: The longitudinal investigation

Read summary

Part 1: Relative age effects and the underdog hypothesis
Although younger players within an age bracket are disproportionately underrepresented in talent pathways for both male and female youth football, there is a growing awareness of the reverse effects this imbalance brings. Research shows that younger players who manage to get into an academy are significantly more likely to receive professional contracts than their older team-mates, and are more likely to transition from a youth football pathway to the senior professional game. These findings strengthen what is known as the "underdog hypothesis". There is a three-fold explanation for this phenomenon, as Adam reveals in his brief.

Part 2: The longitudinal investigation
The investigation has a dual purpose: to test RAEs over twelve seasons, and to examine the birth quartiles (BQs) of academy graduates awarded professional contracts at an English professional football club over eleven seasons. It is a longitudinal study in the sense that its timeframe spans over a decade. Some of the results are striking. For example, once a player is in an English academy, they are five times more likely to receive a professional contract if they are in the youngest BQ than if they are in the oldest BQ. 

Paper citation and link
Kelly, A., Wilson, M. R., Gough, L. A., Knapman, H., Morgan, P., Cole, M., Jackson, D. T., Williams, C. A., 2020, 'A longitudinal investigation into the relative age effect in an English professional football club: Exploring the 'underdog hypothesis'', Science and Medicine in Football, vol. 4, no. 2, pp. 111-118.

Read the full paper here.

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