Relative Age Effect presence at Top 10 Football Soccer UEFA Clubs Youth Academies

Resumen

1 Aim and Research Questions:To what extent is European professional soccer affected by the Relative Age Effect (RAE)?The relative age effect (RAE) consists of the lower presence in any given area, of those bornin the last months closer to the cut-off date, from which a new age category is classified. In thescope of sports and, specifically soccer, the unequal representation of athletes according totheir age and birth month is a matter of concern. This research aims to analyze the birth datesdistribution and RAE by position in the top 10 clubs in the UEFA ranking at the end of the2020/2021 season.1.1 Theoretical Background and Literature Review:The effect of relative age occurs in different areas (e.g. sports, music), being sport, one inwhich it manifests itself most clearly. The first studies on this effect in sport were carried outby Barnsley et al. (1985), who found that 40% of youth ice hockey players in Canada wereborn in the first quarter of the year. In the case of soccer, much research has been developedsince then to try to understand the phenomenon on a deeper level., fFor example, scientificliterature has shown the presence of RAE at in different leagues, clubs, and national teams(Helsen et al., 2005; Pérez-González et al., 2020). This is something affecting not just youthcategories but also can be often found at the senior level, since those who were born at in thefirst quarters of the year were influenced positively in their talent development pathwayfacilitating their reach to the elite senior level. Furthermore, previous studies have looked notjust into the RAE of players collectively but the correlation between RAE and other interestingvariables such as player- specific position or player market value.2. Research Design, Methodology and Data Analysis:The analysis includes all players of the Aacademy of 10 first squads in UEFAs Ranking (atMarch 2021), in 2020 /2021 sSeason. We collect all the information available in open accessfrom academy players (from Under-8 to Under-23) from the respective club's official websites,plus the specialized platform Transfermarkt (2021).The Relative Age Effect (RAE) was detected through Poisson regression (Doyle & Bottomley,2019). At this specific formula y = e (b0 + b1x) explains the frequency count of an event (y)by an explanatory variable x. The data used for Poisson regression were the week of birth(WB) whereby the first week in January was designated WB 1, and time period of birth (tB)describing how far from the beginning of the year a player was born. This last index rangingbetween 0 and 1 was calculated as tB = (WB −0.5)/52. In the Poisson regression, the event (y)was the frequency of birth in a given week and the explanatory variable (x) was tB. The Iindexof discrimination (ID) was also calculated according to Doyle and Bottomley (2019) as e-b1.This index measures the relative odds of a player born on day 1 versus day 365 of thecompetition year being selected. The likelihood ratio D2 was determined according to Cohenet al. (1996). All statistical tests, including descriptive analysis, were performed using thesoftware package R (version 4.0.2). Significance was set at p < 0.05.3.Results,Conclusions, and ImplicationThe study presents the incidence of the Relative Age Effect (RAE) in the Academy teams ofthe top 10 clubs in the UEFA ranking at the end of the 2020/20-21 season. The total samplewas n=1,209 players aged between 8 and 23 years. To verify the presence of RAE, data on thebirths of players was applied in a Poisson regression. The existence of RAE was verified forthe total sample (p<0.001). Segmenting the sample, it was verified that RAE existed in allpositions -goalkeeper, defender, midfielder, and forwards (p<0.001). On the other hand,segmented by clubs: Real Madrid, Bayer Munich, Barcelona, Atlético de Madrid, and Sevillapresented RAE (p<0.001), Juventus (p<0.004), Liverpool (p<0.006), Manchester City(p<0.0025), Manchester United (p<0.011), while Paris Saint Germain was the only club thatdid not present a statistically significant incidence of RAE.If the world of football soccer seeks a more inclusive player participation without a selectionbias affecting youth categories, football soccer governance (i.e. national federations,international institutions, and clubs) should create new regulations that contemplates differentways to avoid the Relative Age Effect from happening. To reach that purpose, future researchshould be developed involving all different stakeholders as well (e.g., coaches, players'associations, etc.).