Skip to main content

Research Repository

Advanced Search

Leveling the Playing Field: A New Proposed Method to Address Relative Age- and Maturity-Related Bias in Soccer

Helsen, Werner; Thomis, Martine; Starkes, Janet; Vrijens, Sander; Ooms, Gerrit; MacMaster, Calum; Towlson, Chris


Werner Helsen

Martine Thomis

Janet Starkes

Sander Vrijens

Gerrit Ooms

Calum MacMaster


Despite various solutions proposed to solve the relative age effect (RAE), it is still a major problem confounding talent identification and selection processes. In the first phase, we sampled 302 under 7–21 academy soccer players from two Belgian professional soccer clubs to explore the potential of a new approach to solve the inequalities resulting from relative age- and maturity-related bias. This approach allocates players into four discrete quartile groups based on the midway point of their chronological and estimated developmental (ED) birth dates (calculated using the growth curves for stature of Belgian youth). With the use of chi square analyses, a RAE was found (p < 0.01) for the overall sample (Q1 = 41.4% vs. Q4 = 14.9%) that completely disappeared after reallocation (Q1 = 26.5%; Q2 = 21.9%; Q3 = 27.5%; Q4 = 24.2%). According to the new allocation method, the stature difference was reduced, on average, by 11.6 cm (from 24.0 ± 9.9 to 12.4 ± 3.4 cm, d = 1.57). Body mass difference between the two methods was 1.9 kg (20.1 ± 11.3–18.2 ± 13.1 kg, respectively, d = 0.15). The new method created a maximum chronological age difference of 1.9 vs. 0.8 years for the current method. With the use of this method, 47% of the players would be reallocated. Twenty-three percent would be moved up one age category, and 21% would be moved down. In the second phase, we also examined 80 UK academy soccer players to explore if reallocating players reduces the within-playing group variation of somatic and physical fitness characteristics. The percentage coefficient of variation (%CV) was reduced (0.2–10.1%) in 15 out of 20 metrics across U11–U16 age categories, with the U13 age category demonstrating the largest reductions (0.9–10.1%) in CV. The U12 and U13 age categories and associated reallocation groupings showed trivial to small (ES = 0.0–0.5) between-method differences and trivial to moderate (ES = 0.0–1.1) differences within the U14–U16 age categories. A reduction in RAE may lead to fewer dropouts and thus a larger player pool, which benefits, in turn, talent identification, selection, and development.


Helsen, W. F., Starkes, J. L., Helsen, W., Thomis, M., Starkes, J., Vrijens, S., …Towlson, C. (2021). Leveling the Playing Field: A New Proposed Method to Address Relative Age- and Maturity-Related Bias in Soccer. Frontiers in Sport and Active Living, 3(24),

Journal Article Type Article
Acceptance Date Jan 22, 2021
Online Publication Date Mar 4, 2021
Publication Date Mar 4, 2021
Deposit Date Mar 4, 2021
Publicly Available Date Mar 4, 2021
Journal Frontiers in Sports and Active Living
Electronic ISSN 2624-9367
Publisher Frontiers Media
Peer Reviewed Peer Reviewed
Volume 3
Issue 24
Article Number 635379
Keywords Relative age effect; Maturity status; Chronological birth date; Developmental birth date; Growth curve; Allocation date; Talent identification
Public URL
Publisher URL


Published article (<nobr>2.2 Mb</nobr>)

Publisher Licence URL

Copyright Statement
Copyright © 2021 Helsen, Thomis, Starkes, Vrijens, Ooms, MacMaster and Towlson. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

You might also like

Downloadable Citations