Variations in the relative age effect with age and sex, and over time—Elite-level data from international soccer world cups

Abstract

The relative age effect (RAE) is a statistical bias observed across sport contexts and consists of a systematic skewness in birth date distribution within an annual-age cohort. In soccer, January 1st is the common cut-off date when categorizing players in competitions according to their chronological age, which potentially disadvantages those within the cohort who were born later in the year. Thus, relatively older soccer players in their cohort can be favored in talent identification, selection, and development. The aim of the current study was to investigate the variations in RAE in male and female international youth world-cup tournaments (U17 and U20) in the period from 1997–2019 and in international senior world-cup-tournaments from 2006–2019. A total of 20,401 soccer players participating in 47 different tournaments were analyzed. The birthdate distributions were categorized into four quartiles (January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4) and compared to a uniform distribution using Chi-square analysis with Cramer’s V (Vc) as a measure of effect size. Based on the existing data concerning RAE in elite junior and senior soccer, it was hypothesized that: (I) the RAE is present in youth soccer world cup tournaments but is stronger in male players than in female players; (II) the younger the soccer players, the stronger the RAE; and (III) the RAE in world cup soccer tournaments has strengthened over time. All these hypotheses were supported by the data; novel findings included that the effect has now entered women’s soccer, and in men’s soccer it persists into senior world cup tournaments. Thus, a strong RAE bias occurs in selection among elite soccer players competing in international world cup tournaments.

Youth-to-senior transition in women’s and girls’ football: Towards a better understanding of relative age effects and gender-specific considerations

“…Nevertheless, the difference in sample selection (i.e., the first one considering the Italian national teams and the second one considering the Italian national teams) may partially explain these results. On the other hand, data corroborated previous results underlined as RAE disappears from youth to senior level [ 20 , 24 ].…”

“…While the RAE is well documented in male football, whereby a consistent and pervasive RAE exists, especially in the youth age groups [ 14 , 18 , 19 ], its presence remains inconclusive in females [ 17 , 21 ]. More specifically, the RAE seems mixed depending on contextual factors such as sociocultural context (i.e., depth of competition, attraction level and country-specific differences) [ 22 ], age groups [ 20 ], competition levels [ 23 ], playing positions [ 20 ], and historical moment [ 24 ]. For example, there was a significant difference in quartile distributions across elite German national teams [ 25 ] (i.e., Q1~31% vs. Q4~21%).…”

“…Similarly, high-level senior French players did not present the RAE [ 26 ] whereas players born near the selection date in Italy were about 1.62 times more likely to reach the high-level tiers [ 27 ]. Likewise, when considering Women’s Football World Cup rosters (years between 2008–2019), the RAE effect sizes have been identified only in the U17 and U20 tournaments but not in senior tournaments [ 20 , 24 ]. In particular, for the Under 17 and 20 age groups, a RAE was observed (i.e., Q1~33% vs. Q4~20%), especially when considering midfielders (i.e., Q1~37% vs Q4~17%) [ 20 ].…”

A Study of Relative Age Effect in Professional Leagues (The Sample of Turkish Super League, 1st League, 2nd League and 3rd League)

“…A statistically significant difference was found between the groups of quarters. In another study (Pedersen et al, 2022) on male football players who participated in the under-17 World Cup between 1997-2019, the number of football players born in the first quarter of the same year was higher than the number of football players born in other quarters.…”

Trends in Relative Age Effects of Top-Level Female Soccer Players: A Japanese Study

“…The relative age effect (RAE) refers to differences in athlete selection that are related to subtle age differences between athletes, such that differences in time of year of the athletes’ births differ within a given age year group (Helsen et al, 2012; Musch & Grondin, 2001; Pedersen, et al, 2022). For example, in Japan, April is the cutoff month for division play because schools begin in April.…”