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The relative age effect (RAE; i.e., an asymmetry in the birth distribution) is a bias observed in sport competitions that may favour relatively older athletes in talent identification. Therefore, the aim of this study was to investigate the presence of RAE in elite soccer players competing in the Italian championships, even considering the discriminations of younger and older Serie A players (in relation to the median age of the sample), and different positional roles (i.e., goalkeeper, defender, midfielder, forward) for each observed category. A total of 2051 players competing into the 2017–2018 Italian under-15 (n = 265), under-16 (n = 362), under-17 (n = 403), Primavera (n = 421) and Serie A (n = 600) championships were analysed. The birth-date distributions, grouped in four quartiles (i.e., January-March, Q1; April-June, Q2; July-September, Q3; October-December, Q4), were compared to a uniform distribution using Chi-squared analysis. The week of birth was analysed using Poisson regression. The results showed a large over-representation of players born in Q1 in all soccer player categories. However, the effect size of this trend resulted smaller as age increased. Individuals born in Q1 have about two-folds more chances to become a Serie A player compared to those born in Q4. The Poisson regression analysis showed that RAE was greater for defenders than for forwards among all categories. Therefore, a strongly biased selection emerged among elite soccer players competing in Italian championships, highlighting how young individuals born in the first three months have many more chances to become elite players compared to the others.
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RESEARCH ARTICLE
The relative age effect is larger in Italian
soccer top-level youth categories and smaller
in Serie A
Paolo Riccardo Brustio
1
, Corrado Lupo
1
*, Alexandru Nicolae Ungureanu
1
,
Riccardo Frati
2
, Alberto Rainoldi
1
, Gennaro Boccia
1
1NeuroMuscularFunction | Research Group, School of Exercise and Sport Sciences, SUISM, Department of
Medical Sciences, University of Torino, Turin, Italy, 2School of Exercise & Sport Sciences, SUISM,
University of Torino, Turin, Italy
*corrado.lupo@unito.it
Abstract
The relative age effect (RAE; i.e., an asymmetry in the birth distribution) is a bias observed
in sport competitions that may favour relatively older athletes in talent identification. There-
fore, the aim of this study was to investigate the presence of RAE in elite soccer players
competing in the Italian championships, even considering the discriminations of younger
and older Serie A players (in relation to the median age of the sample), and different posi-
tional roles (i.e., goalkeeper, defender, midfielder, forward) for each observed category. A
total of 2051 players competing into the 2017–2018 Italian under-15 (n = 265), under-16 (n =
362), under-17 (n = 403), Primavera (n = 421) and Serie A (n = 600) championships were
analysed. The birth-date distributions, grouped in four quartiles (i.e., January-March, Q1;
April-June, Q2; July-September, Q3; October-December, Q4), were compared to a uniform
distribution using Chi-squared analysis. The week of birth was analysed using Poisson
regression. The results showed a large over-representation of players born in Q1 in all soc-
cer player categories. However, the effect size of this trend resulted smaller as age
increased. Individuals born in Q1 have about two-folds more chances to become a Serie A
player compared to those born in Q4. The Poisson regression analysis showed that RAE
was greater for defenders than for forwards among all categories. Therefore, a strongly
biased selection emerged among elite soccer players competing in Italian championships,
highlighting how young individuals born in the first three months have many more chances
to become elite players compared to the others.
Introduction
In Italy, as in most other countries, adolescents and young athletes are grouped according to
their year of birth. Such a categorization of athletes in age groups, based on their chronological
age (e.g., considering as cut-off date January 1
st
), is an usual choice to arrange young athletes
in sports competitions [1,2]. Even though this process is necessary in terms of sport
PLOS ONE | https://doi.org/10.1371/journal.pone.0196253 April 19, 2018 1 / 12
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OPEN ACCESS
Citation: Brustio PR, Lupo C, Ungureanu AN, Frati
R, Rainoldi A, Boccia G (2018) The relative age
effect is larger in Italian soccer top-level youth
categories and smaller in Serie A. PLoS ONE 13(4):
e0196253. https://doi.org/10.1371/journal.
pone.0196253
Editor: Luca Paolo Ardigò, Universita degli Studi di
Verona, ITALY
Received: December 7, 2017
Accepted: April 9, 2018
Published: April 19, 2018
Copyright: ©2018 Brustio et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
files.
Funding: All the funding regarding the realization of
this study were received internally to the authors’
organization (Dr. Lupo’s and Prof. Rainoldi’s
Departmental funding; Department of Medical
Sciences, University of Torino, Turin, Italy). There
was no additional external funding received for this
study.
management [3], there is a difference of almost one year between athletes born close to (e.g.
relatively older athletes) and far away (e.g. relatively younger athletes) the cut-off date and this
could determine crucial consequences in sport career.
The age difference between athletes grouped in the same category (i.e. athletes born in the
same calendar year) has an effect both in terms of physical and psychological maturation [1,
2]. Relatively older athletes are advantaged compared with relatively younger athletes in sport
performance [4], and consequently in the process of sport talent identification [2,3,5]. In fact,
the former subgroup of athletes is more likely to be selected by elite and national teams, and
thus they are more likely to become a professional athlete [1,2,6]. Specifically, the athletes
born close to the cut-off date are more likely to achieve success in sport activities [1]. There-
fore, this asymmetry in the birth distribution is referred as Relative Age Effect (RAE) [7,8],
and it has been initially observed in Canadian ice hockey [7], and other individual [912] and
team [2,1317] sports.
Similar to other sports, soccer is characterized by a significant over-representation of play-
ers born in the early part of the year among young athletes [2,18,19]. However, despite the
pervasive presence of RAE in youth soccer teams, controversial results were found in senior
categories. For example, Gonza
´lez-Vı
´llora and colleagues [13] found no evidence of RAE in
the senior (professional) soccer teams, whereas other studies clearly showed the existence of
this effect in the same category of athletes [20,21].
For Canadian ice hockey [7] and Eighties’ elite soccer players [22], RAE incidence seemed
to progressively decrease as the age category increased, highlighting stronger RAEs in youth
players with respect to senior ones. In particular, having been classified as a strength-based
sport, soccer teams benefit from optimal players’ physical characteristics such body size [23],
aerobic power, muscular strength, endurance, and speed, which are considered as the most
important factors to achieve success [1]. Therefore, in line with these soccer aspects, goalkeep-
ers and defenders (more decisive in the defensive actions) could benefit from optimal physical
characteristics, reporting higher RAEs with respect to midfielders and forwards. However, this
hypothesis has been not fully confirmed by previous studies, where only elite Italian midfield-
ers reported an over-representation of players born in the early part of the selection year [24],
whereas no particular RAE divergence emerged between different tactical roles of the elite
Spanish soccer [19].
In Italy, soccer is the most popular and played sport among young and adult males. Market-
ers, mass-media, and entrepreneurs invest a considerable amount of money in Italian soccer
sponsorship and ownership. The topic of the soccer players’ RAE in Italian youth categories
[2] and senior top professional league (Serie A) has been considered in previous studies [24,
25]. In particular, a study [2] showed an over-representation of players born in the first quar-
tile of the selection year (from January to March) in Italian youth soccer categories (U-15, U-
16, U-17, and U-18), whereas other two works [24,25] reported the same effect for Serie A
players, even highlighting effects in terms of gross wages [24] and tactical roles [25].
However, to the best of our knowledge, no study provided evidence of the RAE for Italian
soccer players of each youth and senior age category of Serie A clubs and among tactical roles.
Thus, this study aimed to investigate: i) the RAE in soccer players of each age category (i.e.,
Under 15, U15; Under 16, U16; Under 17, U17; Under 20, Primavera; and senior top profes-
sional league, Serie A) of clubs competing in Serie A (i.e., the most prestigious senior Italian
soccer championship); ii) even considering the comparison between younger and older Serie A
players’ subgroups established in relation to the median age of the sample; and iii) analyzing if
RAE differences can emerge in relation to different positional roles (i.e., goalkeeper, defender,
midfielder, forward) in each age category. In particular, according to literature on RAE, it has
been hypothesized that: i) elite soccer players competing in Italy and born in the early part of
Relative age effect in Italian soccer
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Competing interests: The authors have declared
that no competing interests exist.
the selection year would be over-represented; ii) RAE would be present in both youth and
senior categories, confirming that this trend is not attenuated in the older athletes; and iii) that
the positional role would not influence the size of RAE.
Materials and methods
Participants
To assess the prevalence of RAEs in players competing in the Italian soccer championships, a
substantial data set has been collected from the web sites of Serie A clubs. The sample consists
of 2064 soccer players competing in the Italian 2017–2018 championships. In particular,
according to the official web site of the Italian Football Federation (http://www.
campionatigiovanili.it/), U15 (n = 265), U16 (n = 362), and U17 (n = 416) were considered as
youth categories, whereas players related to Primavera (n = 421) and Serie A (n = 600) were
included in the study as senior categories.
The study was conducted in accordance with the declaration of Helsinki. Because these
data are based on anonymous resources and publicly available information, no informed con-
sent was requested. However, this study was approved by the local ethics committee of the
University of Torino (Turin, Italy).
Procedure
Young and professional soccer players selected for this study were classified in relation to their
birth-date and positional roles. Successively, all athletes were categorized in four groups based
on their month of birth. Specifically, players born between January and March, April and June,
July and September, and October and December were classified into the quartile 1 (Q1), quar-
tile 2 (Q2), quartile 3 (Q3), and quartile 4 (Q4), respectively.
Even though the Italian nationality was the most represented in the sample (e.g., 45.4% in
Serie A;www.transfermarkt.it/serie-a), a substantial portion of players selected for the present
study were foreign. Thus, according with Delorme and Champely [26] we decide to compare
the distribution of players’ birthdates with a uniform distribution (i.e., Q1 = 25%; Q2 = 25%;
Q3 = 25%; Q4 = 25%). This approach is frequently adopted in the literature for the RAE assess-
ment of international samples.
Furthermore, it has been explored the possibility that the RAE might be more evident in
younger than older Serie A players. For this purpose, the birth-date distributions of two sub-
groups of Serie A players were compared, discriminating participants in relation to the median
age of the sample.
Statistical analysis
Chi-square (χ
2
) tests for U15, U16, U17, Primavera, and Serie A categories were carried out to
investigate the difference in birth-date distribution in the Q1, Q2, Q3, and Q4 quartiles com-
pared to a uniform distribution. In addition, the same statistical approach has been provided
in relation to each positional role (i.e., goalkeeper, defender, midfielder, forward), and for the
younger and older Series A players’ subgroups (after calculating their median age).
For all analyses, the effect size ωof the Chi-square tests was calculated according to Cobley
and colleagues [1] and Brazo-Sayavera and colleagues [9]. In addition, odds ratios (ORs) and
95% confidence intervals (95% CI) were calculated for the first and the last quartile (i.e., Q1
and Q4), as well as for the first and the second semester of the year (i.e., Q1 + Q2 and Q3
+ Q4).
Relative age effect in Italian soccer
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Despite the use of Chi-square tests to assess the RAE has been widely adopted [9,11,13,
15], such method has been criticized because it is considered to have a low statistical power
and to be vulnerable to non-RAE signature [27], making as necessary the application of the
Poisson regression for analyzing low count data [28]. The formula of the Poisson Regression
y = e
(b0 + b1x)
allows to explain the frequency count of an event (y) by an explanatory variable
x. As consequence, the week of born (W
B
) of each player was assessed as follows: players born
between 1
st
and 7
th
January were categorized in W
B
1, players born between 8
th
and 14
th
Janu-
ary were categorized in W
B
2 and so on.
The time of birth (t
B
) was computed according to the formula t
B
= (W
B
0.5) / 52. In par-
ticular, t
B
measures how far from the beginning of the year a player was born, and it is ran-
ged between 0 and 1. Successively, using a Poisson regression to count data, it has been
calculated how the frequency of birth in a given week (y) was explained by the t
B
(x). Addi-
tionally, according to Doyle and Bottomley [28], the Index of Discrimination (ID) was cal-
culated as e
-b1
. The ID provides the relative odds of being selected for a player born on day 1
versus day 365 of the competition year [28]. Likelihood ratio R
2
was computed according to
Cohen and colleagues [29].
Statistical analyses were conducted using Statistical Package for Social Sciences, version
24.0 (SPSS Inc, Chicago, IL, USA) and GraphPad Prism (San Diego, California, USA). For all
tests, the level of significance was fixed at α0.05.
Results
The observed quarterly birth rate distribution of the participants for U15, U16, U17, Prima-
vera, and Serie A is separately displayed in Fig 1.
Fig 1. Birth date distribution of soccer players competing in the Italian championship. Quarterly birth date distribution of soccer players competing in the
Italian U15, U16, U17, Primavera, and Serie A. The uniform distribution was of 25% for each quartile. Quartile 1 (Q1), 2 (Q2), 3(Q3), 4 (Q4).
https://doi.org/10.1371/journal.pone.0196253.g001
Relative age effect in Italian soccer
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Table 1 shows the pertinent statistical analysis in relation to the overall sample and different
positional roles (i.e., goalkeeper, defender, midfielder, forward).
The observed distributions for U15, U16, U17, Primavera, and Serie A were significantly
different from the uniform distribution (all Pvalues <0.0001). Specifically, an over-represen-
tation of soccer players born in Q1 (overall mean 43.3%) and Q2 (overall mean 27.4%) was
observed. Differently, an under-representation of players born in Q3 (overall mean 18.6%)
and Q4 (overall mean 10.7%) was reported. Interestingly, the effect size of the RAE (as well as
the ORs) resulted lower for higher progressive age categories, with the exception of Primavera,
which reported a little higher value with respect to the U17 one.
Overall, the positional role did not influence the effect size of the RAE, with the exception
of U15. Indeed, when considering the ωand ORs, the U15 goalkeepers and defenders showed
larger RAE than midifielders and forwards (Table 1). All other age categories did not show
marked difference among tactical roles (Table 1).
The calculation of the median age of the Italian Serie A soccer players defined <and 25
years old players as younger and older, respectively. For the RAE distribution of younger and
older Serie A players, differences emerged with respect to the uniform distribution for both
subgroups (Table 2). Nevertheless, no difference was reported in comparing the RAE of youn-
ger and older subgrougs (χ
2
= 2.1, P= 0.532, Q1/Q4 OR 1.2, CI0.7–2.0, OR (Q1+Q2)/(Q3
+Q4) 1.0, CI 0.7–1.4.
Table 1. Unadjusted odds ratios (ORs, 95% CI) for soccer players examining relative age effect.
Under 15 Under 16 Under 17 Primavera Serie A
Overall χ
2
60.5 74.4 43.9 53.5 27.7
Pvalue <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
ω0.47 0.45 0.33 0.36 0.22
OR Q1/Q4 9.8 (5.1–19.1) 7.5 (4.5–12.6) 4.0(2.6–6.1) 4.3 (2.8–6.6) 2.3 (1.6–3.2)
OR (Q1+Q2)/(Q3+Q4) 3.6 (2.4–5.2) 3.3 (2.4–4.5) 2.4 (1.8–3.3) 2.5 (1.8–3.3) 1.7 (1.4–2.1)
Goalkeeper χ
2
10.64 8.7 11.6 7.42 8.4
Pvalue 0.0138 0.034 0.0091 0.0596 0.0392
ω0.68 0.50 0.51 0.31 0.35
OR Q1/Q4 31 (1.5–634.9) 9.5 (1.7–53.4) 21 (2.4–18436) 4.4 (1.2–15.6) 4.0 (1.5–11.0)
OR (Q1+Q2)/(Q3+Q4) 4.8 (1.2–18.2) 3.4 (1.2–9.4) 2.4 (1–5.7) 1.6 (0.7–3.8) 2.2 (1.1–4.3)
Defender χ
2
24.0 23.2 18.6 17.3 7.3
Pvalue <0.0001 <0.0001 0.0003 0.0006 0.006
ω0.59 0.47 0.38 0.37 0.19
OR Q1/Q4 19.5 (4.0–94) 10.2 (3.5–29.7) 5.1 (2.3–11.5) 4.5 (2.0–10) 2.0 (1.2–3.7)
OR (Q1+Q2)/(Q3+Q4) 5.9 (2.6–13.4) 3.2 (1.7–5.7) 2.8 (1.6–4.7) 2.8 (1.6–4.7) 1.7 (1.2–2.5)
Midfielder χ
2
17.2 25.7 13.0 18.7 8.7
Pvalue 0.0006 <0.0001 0.0047 0.0003 0.0332
ω0.49 0.49 0.31 0.35 0.21
OR Q1/Q4 12 (3.1–46.2) 7.7 (3.0–20) 2.4 (1.2–4.9) 4.5 (2.2–9.2) 2.2 (1.3–3.9)
OR (Q1+Q2)/(Q3+Q4) 3.2 (1.6–6.6) 4.2 (2.3–7.7) 2.5 (1.5–4.1) 2.3 (1.4–3.6) 1.7 (1.2–2.6)
Forward χ
2
6.6 13.9 12.1 14.6 5.5
Pvalue 0.0868 0.0031 0.0071 0.022 0.1404
ω0.36 0.39 0.35 0.38 0.20
OR Q1/Q4 3.6 (1.0–12.6) 5.4 (2.1–13.9) 4.2 (1.8–9.9) 3.9 (1.7–9.1) 2.1 (1.1–4.2)
OR (Q1+Q2)/(Q3+Q4) 2.7 (1.2–6.2) 2.2 (1.2–4.1) 2.2 (1.2–3.8) 2.9 (1.6–5.5) 1.7 (1.0–2.7)
Quartile 1 (Q1), 2 (Q2), 3 (Q3), 4 (Q4).
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Relative age effect in Italian soccer
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Table 3 shows the mean and standard deviation of W
B
and t
B
, as well as the results of Pois-
son regression for each category. The scatterplot of relative birth frequency by week is reported
in Fig 2. The findings from this analysis were in general similar to those coming from the Chi-
squared analysis. Indeed, in general, the frequency of t
B
was higher at the beginning of the year
compared to the end of the year. Furthermore, ID showed that the players born right at the
start of the year were 8.93 times more likely to be included in Under 15 than those born at the
end of the years, 11.88 times more likely to be included in Under 16, 9.47 times more likely to
be included in Under 17, 9.47 times more likely to be included in Primavera, and only 3.12
times more likely to be included in Serie A.
The position role had affected the amount of RAE in all categories. In fact, the Poisson
regressions were not significant (P 0.09, R
2
0.30) in goalkeepers from under 15 to Prima-
vera. However, in goalkeepers the results were likely affected by the small sample sizes. Indeed,
t
B
indexes were low (0.30) for all categories, suggesting the times of birth were markedly
skewed towards the first part of the year. Beyond this, IDs were overall higher in defenders
(ranged 4.37–6.28) than in forwards (ranged 1.98–3.91). The IDs of midfielders showed more
scattered results (ranged 2.43–7.58).
Discussion
The aim of this study was to examine the incidence of RAE in elite Italian soccer clubs, both
for young and senior soccer players. For this purpose, the birth-date distribution of players
competing in Serie A clubs has been investigated considering both senior and youth categories.
A large over-representation of athletes born close to the cut-off date (i.e., the beginning of the
calendar year) strongly emerged in youth teams. Coherently, this trend is maintained in senior
elite teams of Serie A, though to a less extent, accepting the first hypothesis.
A very large RAE was found in all considered youth categories (i.e., U15, U16, U17) and
Primavera (Figs 1and 2). In fact, these results revealed a biased distribution [19] in Italian soc-
cer leagues with an over-representation of athletes born in the first part of the calendar year.
Similar results were previously found in youth soccer categories in European context [2,13,
15,1821]. RAE in team sports is influenced by different factors, including physical, psycho-
logical, and environmental aspects, or by their combination [1,6,8,30]. In particular, in inva-
sion sports, such as soccer, the physical maturation of individuals influences the muscular
strength, endurance, and speed, which are important factors for a successful performance [1,
8]. Thus, relatively older young soccer players are favoured due to their advanced anthropo-
metric development (e.g., body mass, stature) and a superior soccer-specific strength and
endurance compared with their younger counterparts [31,32]. These findings underline that
the differences in maturity status within age groups negatively affects talent identification due
to the greater chance for relative older athletes to be selected. In this sense, more opportunities
to play, practise, and train are provided to young athletes with a more advanced physical matu-
rity. Consequently, they might have more chances to become elite senior athletes.
Table 2. Relative age effect (RAE) differences between younger and older soccer players playing in Serie A.
Serie A Younger (<25 yrs) Older (25 yrs)
χ
2
16.2 12.7
Pvalue 0.0011 0.0054
ω0.23 0.20
OR Q1/Q4 2.6 (1.6–4.2) 2.1 (1.3–3.3)
OR (Q1+Q2)/(Q3+Q4) 1.8 (1.3–2.5) 1.8 (1.3–2.5)
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Relative age effect in Italian soccer
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A marked RAE is still present in elite senior players of Serie A teams (Figs 1and 2). This is
evidenced by both the Chi-squared (Table 1) and Poisson regression analysis (Table 2). The
Poisson regression has been recently proposed as a powerful statistical mean to assess the RAE
[28]. Thanks to this analysis it has been possible to calculate that the players born close to the
beginning of the year are 3.1 times more likely to play in Serie A than the players born close to
the end of the year, as highlighted by the corresponding ID value in Table 2. This means that
the biased selection of talented players in youth categories has an effect even in senior teams,
thus highlighting that athletes born close to the beginning of the calendar year are more likely
to achieve success in adult sport compared to the relatively younger ones [1]. Therefore, this
Table 3. Relative age effect (RAE) according to the Poisson regression in each category and positional role.
Under 15 Under 16 Under 17 P rimavera Serie A
Overall W
B
16±14 16±13 19 ±14 19 ±14 22 ±15
t
B
0.30 ±0.27 0.30 ±0.25 0.35 ±0.26 0.36 ±0.27 0.41 ±0.28
b
0
2.573 2.954 2.989 2.87 2.961
b
1
-2.189 -2.475 -2.248 -1.840 -1.137
ID 8.93 11.88 9.47 6.30 3.12
R
2
0.67 0.76 0.66 0.64 0.53
Pvalue <0.0001 <0.0001 <0.0001 <0.0001 <0.0001
Goalkeeper W
B
13 ±10 16 ±13 17 ±12 19 ±14 19 ±3
t
B
0.23 ±0.20 0.29 ±0.24 0.32 ±0.24 0.35 ±0.26 0.35 ±0.27
b
0
0.548 0.676 0.788 0.987 1.092
b
1
-0.969 -0.679 -0.867 -0.912 -1.086
ID 2.64 1.97 2.38 2.49 2.96
R
2
0.30 0.11 0.12 0.28 0.22
Pvalue 0.366 0.327 0.085 0.090 0.023
Defender W
B
14 ±11 16 ±13 18 ±13 19 ±14 22 ±15
t
B
0.26 ±0.22 0.30 ±0.24 0.34 ±0.26 0.36 ±0.26 0.42 ±0.28
b
0
1.431 1.617 1.621 1.588 1.771
b
1
-1.75 -1.837 -1.476 -1.481 -0.948
ID 5.76 6.28 4.37 4.40 2.58
R
2
0.54 0.43 0.38 0.43 0.22
Pvalue 0.002 <0.0001 <0.0001 <0.0001 <0.0001
Midfielder W
B
17 ±13 16 ±12 20 ±15 19 ±14 22 ±15
t
B
0.32 ±0.25 0.29 ±0.24 0.38 ±0.28 0.36 ±0.27 0.41 ±0.28
b
0
1.247 1.70 1.620 1.757 1.780
b
1
-1.378 -2.026 -1.231 -1.405 -0.886
ID 3.97 7.58 3.43 4.07 2.43
R
2
0.40 0.52 0.37 0.42 0.23
Pvalue 0.004 <0.0001 <0.0001 <0.0001 0.001
Forward W
B
20 ±13 18 ±14 19 ±14 19 ±14 22 ±15
t
B
0.37 ±0.24 0.33 ±0.27 0.35 ±0.26 0.35 ±0.27 0.41 ±0.28
b
0
0.754 1.271 1.445 1.374 1.419
b
1
-0.681 -1.188 -1.363 -1.169 -0.892
ID 1.98 3.28 3.91 3.22 2.44
R
2
0.11 0.17 0.30 0.21 0.20
Pvalue 0.218 0.008 <0.0001 0.004 0.004
Notes: W
B
, week in which players born; t
B
, time of birth; ID, Index of Discrimination.
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Relative age effect in Italian soccer
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trend appears as controversial with respect to what has been described in a recent review on
RAE in youth and elite soccer [33], which highlighted that no significant RAE was found in
elite soccer teams due to the fact that physical advantages do not exist in older players.
In addition, the absence of differences for the prevalence of RAE of younger (<25 years)
and older (25 years) Serie A players strengthened how such trend is not attenuated in older
athletes, confirming what has been reported in the second hypothesis. In other words, the ini-
tial selection of Serie A players, which is biased by the RAE, results in a long-time effect, and
the individuals born in the second part of the calendar year show fewer chances to become
Serie A players even in later part of their career. Moreover, the extent of RAE in senior teams
was much smaller than in youth categories. It is likely that for the athletes born late in the year,
the chance to be identified and selected as elite increases as the age increases. Indeed, the small
difference in age and, as a consequence, in maturation status, has a smaller effect in physical
performance of adult players. Finally, it must be considered that the massive presence of for-
eign players in senior teams could potentially determine a relevant influence on the RAE of the
Serie A soccer players. In fact, the extent of RAE differs across countries because of physical
and socio-cultural factors [6,34].
The players born in Q1 are 10-folds more represented than those born in Q4 in U15 cate-
gory (as reported by the Q1/Q4 ORs in Table 1). This ratio progressively decreases as age
increases, but remains very large across all youth categories, confirming the same trends
already reported for Canadian ice hockey [7] and Eighties’ elite soccer players [22]. Indeed, in
Primavera the players born in Q1 are 4-folds more represented than those born in the Q4. The
same trend, i.e. RAE decreases as age increases, was evidenced by the Poisson regression analy-
sis (as reported by the IDs in Table 2). The larger RAE, observed in the pubertal phase, sup-
ports the maturation-selection hypothesis [1,9]. This means that the biased selection of young
talented players is much more evident in the early adolescence where any little inter-individual
age difference can determine a substantial difference in terms of body maturation.
Fig 2. Scatterplot of RAE frequency by week. Scatterplot of RAE frequency by week of year for U15, U16, U17, Primavera, and Serie A. The red line represents the best
fit of the Poisson regression.
https://doi.org/10.1371/journal.pone.0196253.g002
Relative age effect in Italian soccer
PLOS ONE | https://doi.org/10.1371/journal.pone.0196253 April 19, 2018 8 / 12
The findings regarding the positional role are more difficult to interpret, mostly because the
small sample sizes available for some roles (e.g. goalkeepers) made the analysis less statistically
powerful. Nevertheless, for the U15 league, the RAE in goalkeepers and defenders was larger
than that in midfielders and forwards (Tables 1and 2), thus suggesting that the more pro-
nounced body maturation of early-born players has more positive effect for athletes that play
closer to the opponents’ soccer goal. Regarding the other categories (i.e. U16, U17, Primavera,
and Serie A), the results would be slightly different if considering Poisson regression or Chi-
squared analysis. Indeed, IDs coming from the Poisson regression analysis are consistently
higher for defenders than for forwards (Table 2). This means that, in line with a previous study
on elite Italian soccer players [25], the soccer players’ body size could be associated to RAE
and coaches’ selection, regardless of references to real performance [23]. Conversely, the Chi-
squared analysis did not show a clear trend in differentiating the position roles among age cat-
egories (Table 1). A systematic comparison between the two statistical approaches is beyond
the scope of this study though. However, since the Poisson regression has been suggested to
have more statistical power than Chi-squared analysis, we can conclude that the size of RAE
was greater in defenders than in forwards in all categories.
The results of this study showed how RAE is a relevant factor in reaching success in Italian
soccer competitions. This process leads to a vicious circle where early-born children have an
increased and persistent advantage over late-born children in sports [2]. Consequently, the
selection bias associated with the RAE should be taken into account for talent identification
(e.g., knowledge of birthdates of the players or ordered of shirt numbers according to player’s
age) [35].
Some limitations of this study should be underlined. First, we collected players’ information
at the beginning of the season (i.e., at the end of August 2017), which may be not fully repre-
sentative of the entire competitive period (i.e. August 20
th
, 2017 –May 20
th
, 2018). In fact, sev-
eral players in Serie A, moved to different clubs during a specific winter period dedicated to
these exchanges, determining heterogeneous team rosters along the same season. Second, the
present data refer to only one season, making difficult to understand if the RAE is getting
worse over time. Therefore, further studies should provide wider scenarios able to show data
from different Italian soccer categories along several seasons. Moreover, the present study
focused only on male athletes, highlighting the need to investigate the possible gender differ-
ence in the Italian context, in line with previous studies [9,36]. Then, to assess the players’
RAE, it has been only considered the birthdate, avoiding any reference to the individual per-
formance (e.g., number of the match involvement or total minutes played during a season)
[17] or salary engagements [24], highlighting how this additional information might be useful
to better describe RAE.
For all these reasons, similar analyses in different countries should be promoted. In fact,
controversial effects could be unexpectedly observed in relation to different factors such as the
players’ earnings [18], and salaries [37]. As consequence, any discordance of results could
encourage future investigations on potential training and selection aspects that affect RAE
mechanisms.
In terms of methodology, youth players who participated in two championships were con-
sidered twice (as different individuals), despite they represented the 4.3% of all selected youth
soccer players. Moreover, the data analyses were applied considering the reference to the Ital-
ian population, despite the relevant presence of non-Italian players, who probably experienced
different age-category cut-offs along a different talent process. Finally, restricted U15 (216
over 265 players; 81.5% of all players selected for this subcategory), U16 (241 over 265 players;
93.4%), and Primavera (599 over 600 players; 99.9%) samples were considered for the analysis
on RAE in relation to tactical roles, due to lack of information.
Relative age effect in Italian soccer
PLOS ONE | https://doi.org/10.1371/journal.pone.0196253 April 19, 2018 9 / 12
In conclusion, it has to highlight that this is only the second paper which applied the Pois-
son regression [28], and how future studies on this topic will be able to consolidate this statisti-
cal procedure as more statistically power than Chi-squared analysis to elaborate RAE effects
on the concept of Index of Discrimination.
Conclusions
The birth-date distribution of young soccer players clearly showed a large over-representation
of athletes born in the first semester of the year (i.e., Q1 and Q2). This trend is maintained, to
a less extent, in senior elite teams of Serie A. Therefore, in Italian soccer context, the relatively
older individuals have more chances to be selected by elite teams, both in young and senior
categories. In fact, this selection bias, known as RAE, limits the possibility to potentially select
talented athletes born late in the year of consideration. In addition, this selection bias could be
influenced by the positional role, being greater in defenders than in forwards.
In conclusion, especially during the first years of soccer practice, coaches and physical train-
ers of soccer clubs should be aware that the players, born at the ending months of a year, even
though are characterized by a not so successful performance (as consequence of lower values
in body parameters, such as stature and body mass, as well as reduced physical and technical
capabilities), could demonstrate high improvements for these aspects even in a close future.
Therefore, the avoiding of this bias selection could effectively promote the grown of an entire
national soccer system.
Supporting information
S1 Table. Data from participants in this study.
(PDF)
Author Contributions
Conceptualization: Paolo Riccardo Brustio, Gennaro Boccia.
Data curation: Paolo Riccardo Brustio, Alexandru Nicolae Ungureanu, Riccardo Frati, Gen-
naro Boccia.
Formal analysis: Gennaro Boccia.
Funding acquisition: Corrado Lupo, Alberto Rainoldi.
Investigation: Paolo Riccardo Brustio, Gennaro Boccia.
Supervision: Corrado Lupo, Alberto Rainoldi, Gennaro Boccia.
Writing – original draft: Paolo Riccardo Brustio.
Writing – review & editing: Paolo Riccardo Brustio, Corrado Lupo, Alexandru Nicolae
Ungureanu, Riccardo Frati, Alberto Rainoldi, Gennaro Boccia.
References
1. Cobley S, Baker J, Wattie N, McKenna J. Annual age-grouping and athlete development: a meta-analyt-
ical review of relative age effects in sport. Sports Med. 2009; 39(3):235–56. https://doi.org/10.2165/
00007256-200939030-00005 PubMed Central PMCID: PMC19290678. PMID: 19290678
2. Helsen WF, Van Winckel J, Williams AM. The relative age effect in youth soccer across Europe. J
Sports Sci. 2005; 23(6):629–36. https://doi.org/10.1080/02640410400021310 PubMed Central PMCID:
PMC16195011. PMID: 16195011
Relative age effect in Italian soccer
PLOS ONE | https://doi.org/10.1371/journal.pone.0196253 April 19, 2018 10 / 12
3. Rubajczyk K, Swierzko K, Rokita A. Doubly Disadvantaged? The Relative Age Effect in Poland’s Bas-
ketball Players. Journal of sports science & medicine. 2017; 16(2):280–5. PMID: 28630582; PubMed
Central PMCID: PMC5465991.
4. Cobley S, McKenna J, Baker J, Wattie N. How pervasive are relative age effectsin secondary school
education? J Educ Psychol. 2009; 101(2):520. https://doi.org/10.1037/a0013845
5. Votteler A, Honer O. The relative age effect in the German Football TID Programme: biases in motor
performance diagnostics and effects on single motor abilities and skills in groups of selected players.
Eur J Sport Sci. 2014; 14(5):433–42. https://doi.org/10.1080/17461391.2013.837510 PMID: 24047192;
PubMed Central PMCID: PMC24047192.
6. Wattie N, Schorer J, Baker J. The relative age effect in sport: A developmental systems model. Sports
Med. 2015; 45(1):83–94. https://doi.org/10.1007/s40279-014-0248-9 PMID: 25169442
7. Barnsley RH, Thompson AH, Barnsley PE. Birthdate and performance: The relative age effect. Can J
Hist Sport Phys Educ. 1985; 51:23–8.
8. Musch J, Grondin S. Unequal Competition as an Impediment to Personal Development: A Review of
the Relative Age Effect in Sport. Dev Rev. 2001; 21(2):147–67. https://doi.org/10.1006/drev.2000.0516
9. Brazo-Sayavera J, Martinez-Valencia MA, Muller L, Andronikos G, Martindale RJJ. Identifying talented
track and field athletes: The impact of relative age effect on selection to the Spanish National Athletics
Federation training camps. J Sports Sci. 2017; 35(22):2172–8. https://doi.org/10.1080/02640414.2016.
1260151 PMID: 27879175.
10. Costa AM, Marques MC, Louro H, Ferreira SS, Marinho DA. The relative age effect among elite youth
competitive swimmers. Eur J Sport Sci. 2013; 13(5):437–44. https://doi.org/10.1080/17461391.2012.
742571 PubMed Central PMCID: PMC24050459. PMID: 24050459
11. Muller L, Hildebrandt C, Schnitzer M, Raschner C. The Role of a Relative Age Effect in the 12th Winter
European Youth Olympic Festival in 2015. Percept Mot Skills. 2016; 122(2):701–18. https://doi.org/10.
1177/0031512516640390 PMID: 27166343.
12. Fukuda DH, Kelly JD, Albuquerque MR, Stout JR, Hoffman JR. Relative age effects despite weight cat-
egories in elite junior male wrestlers. Sport Sci Health. 2017; 13(1):99–106. https://doi.org/10.1007/
s11332-017-0351-z
13. Gonzalez-Villora S, Pastor-Vicedo JC, Cordente D. Relative Age Effect in UEFA Championship Soccer
Players. Journal of human kinetics. 2015; 47:237–48. https://doi.org/10.1515/hukin-2015-0079 PMID:
26557207; PubMed Central PMCID: PMC4633259.
14. Vincent J, Glamser FD. Gender differences in the relative age effect among US olympic development
program youth soccer players. J Sports Sci. 2006; 24(4):405–13. https://doi.org/10.1080/
02640410500244655 PMID: 16492604.
15. Delorme N, Boiche J, Raspaud M. The relative age effect in elite sport: the French case. Res Q Exerc
Sport. 2009; 80(2):336–44. https://doi.org/10.1080/02701367.2009.10599568 PMID: 19650399.
16. Jones BD, Lawrence GP, Hardy L. New evidence of relative age effects in "super-elite" sportsmen: a
case for the survival and evolution of the fittest. J Sports Sci. 2017:1–7. https://doi.org/10.1080/
02640414.2017.1332420 PMID: 28627293.
17. Vaeyens R, Philippaerts RM, Malina RM. The relative age effect in soccer: a match-related perspective.
J Sports Sci. 2005; 23(7):747–56. https://doi.org/10.1080/02640410400022052 PMID: 16195025.
18. Ashworth J, Heyndels B. Selection bias and peer effects in team sports: The effect of age grouping on
earnings of German soccer players. J Sports Econom. 2007; 8(4):355–77. https://doi.org/10.1177/
1527002506287695
19. Gutierrez Diaz Del Campo D, Pastor Vicedo JC, Gonzalez Villora S, Contreras Jordan OR. The relative
age effect in youth soccer players from Spain. Journal of sports science & medicine. 2010; 9(2):190–8.
https://doi.org/10.1111/j.1600-0838.2009.00961.x PMID: 24149685; PubMed Central PMCID:
PMC3761747.
20. Helsen WF, Starkes JL, Van Winckel J. The influence of relative age on success and dropout in male
soccer players. American journal of human biology: the official journal of the Human Biology Council.
1998; 10(6):791–8. https://doi.org/10.1002/(SICI)1520-6300(1998)10:6<791::AID-AJHB10>3.0.CO;2–
1PMID: 28561412.
21. Mujika I, Vaeyens R, Matthys SP, Santisteban J, Goiriena J, Philippaerts R. The relative age effect in a
professional football club setting. J Sports Sci. 2009; 27(11):1153–8. https://doi.org/10.1080/
02640410903220328 PMID: 19714545.
22. Barnsley RH, Thompson AH, Legault P. Family Planning: Football Style. The Relative Age Effect in
Football. Int Rev Sociol Sport. 1992; 27(1):77–87. https://doi.org/10.1177/101269029202700105
Relative age effect in Italian soccer
PLOS ONE | https://doi.org/10.1371/journal.pone.0196253 April 19, 2018 11 / 12
23. Furley P, Memmert D. Coaches’ implicit associations between size and giftedness: implications for the
relative age effect. J Sports Sci. 2016; 34(5):459–66. https://doi.org/10.1080/02640414.2015.1061198
PMID: 26096053.
24. Fumarco L, G. R. Relative age effect on labor market outcomes for high skilled workers–evidence from
soccer. Working Papers in Management—University of London, Birkbeck, BWPMA 1501. 2015.
http://www.bbk.ac.uk/management/docs/workingpapers/WP9.pdf.
25. Salinero JJ, Pe
´rez B, Burillo P, ML L. Relative age effect in european professional football: Analysis by
position. J Hum Sport Exerc. 2013; 8(4):966–73. https://doi.org/10.4100/jhse.2013.84.07
26. Delorme N, Champely S. Relative Age Effect and chi-squared statistics. Int Rev Sociol Sport. 2013; 50
(6):740–6. https://doi.org/10.1177/1012690213493104
27. Loffing F. Commentary: "How Much is that Player in the Window? The One with the Early Birthday?"
Relative Age Influences the Value of the Best Soccer Players, but Not the Best Businesspeople. Front
Psychol. 2016; 7:620. https://doi.org/10.3389/fpsyg.2016.00620 PMID: 27199851; PubMed Central
PMCID: PMCPMC4849242.
28. Doyle JR, Bottomley PA. Relative age effect in elite soccer: More early-born players, but no better val-
ued, and no paragon clubs or countries. PloS One. 2018; 13(2):e0192209. https://doi.org/10.1371/
journal.pone.0192209 PMID: 29420576
29. Cohen J, Cohen P, West SG, Aiken LS. Applied multiple regression/correlation analysis for the behav-
ioral sciences: Routledge; 2013.
30. Reed KE, Parry DA, Sandercock GR. Maturational and social factors contributing to relative age effects
in school sports: Data from the London Youth Games. Scand J Med Sci Sports. 2016. https://doi.org/
10.1111/sms.12815 PMID: 28000283.
31. le Gall F, Carling C, Williams M, Reilly T. Anthropometric and fitness characteristics of international, pro-
fessional and amateur male graduate soccer players from an elite youth academy. Journal of science
and medicine in sport. 2010; 13(1):90–5. https://doi.org/10.1016/j.jsams.2008.07.004 PMID: 18835220;
PubMed Central PMCID: PMC18835220.
32. Carling C, le Gall F, Reilly T, Williams AM. Do anthropometric and fitness characteristics vary according
to birth date distribution in elite youth academy soccer players? Scand J Med Sci Sports. 2009; 19(1):3–
9. https://doi.org/10.1111/j.1600-0838.2008.00867.x PMID: 19000100.
33. Sierra-Dı
´az MJ, Gonza
´lez-Vı
´llora S, Pastor-Vicedo JC, Serra-Olivares J. Soccer and Relative Age
Effect: A Walk among Elite Players and Young Players. Sports. 2017; 5(1):5.
34. Hancock DJ, Adler AL, Cote J. A proposed theoretical model to explain relative age effects in sport. Eur
J Sport Sci. 2013; 13(6):630–7. https://doi.org/10.1080/17461391.2013.775352 PMID: 24251740;
PubMed Central PMCID: PMC24251740.
35. Mann DL, van Ginneken PJ. Age-ordered shirt numbering reduces the selection bias associated with
the relative age effect. J Sports Sci. 2017; 35(8):784–90. https://doi.org/10.1080/02640414.2016.
1189588 PMID: 27238077.
36. Boccia G, Rainoldi A, Brustio PR. Relative age effect in males, but not females, undergraduate students
of sport science. Sport Sci Health. 2017; 13(2):349–53. https://doi.org/10.1007/s11332-017-0364-7
37. Fumarco L, Rossi G. The relative age effect on labour market outcomes–evidence from Italian football.
Eur Sport Manag Q. 2018. https://doi.org/10.1080/16184742.2018.1424225
Relative age effect in Italian soccer
PLOS ONE | https://doi.org/10.1371/journal.pone.0196253 April 19, 2018 12 / 12

Supplementary resource (1)

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The Relative Age Effect (RAE) has been the subject of many studies, but few have focused on professional athletes in individual sports. The aim of this study was to verify the existence of the RAE among elite senior female tennis players (top 100 players) in the WTA Rankings ( n = 1000) in the years 2007–2016. The analysis was performed among top 100, resp. top 10 female tennis players, among players in 4 age subgroups and among left-handed (LH) and right-handed (RH) players. The existence of the RAE was assessed with the use of chi-square test (goodness of fit). More than half of top 100 players were born in first semester: both in individual years (53.0–63.0%) and in the whole observed period (58.4%). Significant RAE (ES medium) was observed in top 100 female players only in 2012 and 2016; significant RAE (ES small) was detected in the period of 2007–2016. Among the top 10 players, significant RAE (ES medium) was demonstrated during the whole period. No significant RAE (ES medium) was detected in the 17–18y subgroups, significant in 19–24y and 25–30y (ES small) as well as in 31–36y (ES medium). Although significant RAE was observed in the subgroups of LH and RH female players, ES was large only in the LH. The results contribute to the expansion of the knowledge about the reduction of the RAE existence in adulthood among coaches, athletes and tennis officials.
... The lack of RAE observed in senior male players as they transition from youth to senior level is consistent with previous observations of soccer nations such as Germany [7]. When considering the selection bias at the youth level (e.g., U17, U19), this reduction in RAE prevalence at senior levels challenges the efficacy of this (un)conscious bias and raises awareness of this process relative to long-term development and success [7,36,37]. ...
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The relative age effect (RAE) is characterised by an overrepresentation of athletes born earlier in the selection year. Whilst an RAE is consistently evident in male soccer, examinations in female players remain limited. The aim of the present study was to examine the influence of sex, as well as age, success, and playing status in European soccer players. The sample consisted of a total of 6546 soccer players from 55 soccer nations that competed in recent European Championship qualification campaigns. Results indicated an evident RAE in male [p = 0.017] but not female [p = 0.765] players. Male players were over-represented by players born in the first quartile for the U17 [p < 0.001] and U19 [p = 0.001] levels, however, this over-representation did not transfer to senior levels. No RAE was observed at any level for female players. Inside each age group, a slight selection bias towards those born in the first quartile for successful squads was observed but did not significantly differentiate between qualification status for either male or female players. Results from this study highlight the disparity in RAE prevalence between male and female players and raise further questions regarding the value of selecting relatively older players to metrics of success, transition, and selection for senior international soccer.
... A player is more likely to be talented if they retain desirable anthropometry rather than skill from an early age. Considering that the influence of RAE tends to decrease with age but does not disappear [5,6], the likelihood of high-ability athletes dropping out in the future is very high. Over time, the less mature athletes drop out of the sport because they are not as successful, motivated, or fulfilled by the experience in their younger years of competition [7]. ...
... Mean values for relative age across the Irish pathway differed from the expected values for relative age by only a small degree. When examining the playing population in the Irish pathway by birth quartile, the proportion of youth players born in the last two quartiles of the year is higher than those previously observed elsewhere, 5,6,24,[41][42][43] although the majority of Irish players were born in Q1 and Q2. Accordingly, one might argue that variance in maturation presents a greater challenge for selectors than the variance in relative age within this particular sample. ...
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This study investigated the associations between biological maturation status (classified using the Khamis-Roche method for the percentage of predicted adult height at the time of observation) and relative age (expressed as a decimal value relative to the difference between birth date and competition cutoff date) and the extent to which their relative selection biases existed across competitive age groups in an analysis of players within the Football Association of Ireland's (FAI) national talent pathway. The players assessed were either from the U13 FAI National Academy (n = 125), the Ireland U15 national team (n = 18), or the Ireland U16 national team (n = 16). A moderate to very large selection bias in favour of early maturing players was observed across all age groups, increasing in magnitude with successive age groups (p < 0.05). A total of 46-72% of players selected into the national talent pathway were early maturing; 0% of U15 and U16 players were late maturing. A relative age effect existed across all competitive cohorts (p < 0.05), although not increasing with chronological age and smaller in magnitude than maturation biases. A small positive correlation between relative age and absolute maturity status at U13 was observed, and an inverse correlation between relative age and relative maturity status at U15 (p < 0.01) was observed. There were no other significant correlations between relative or absolute maturity status and relative age. We encourage Football Associations to critically reflect upon their criteria for national talent squad selection; the current system diminishes the chances of selection for late maturing players.
... During puberty, the RAE is often found to be strongest in this period related to the large variation in physique and anthropometry due to age [10]. After puberty, RAE are often found to subside [11], however, secondary effects may maintain the persistence during senior carrier [12]. Early maturation and success may increase training motivation and thus the sport-specific skills and experience [11,13]. ...
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Introduction Earlier studies have demonstrated that the oldest in a competition class are more likely to succeed than the youngest, a phenomenon called relative age effect (RAE). Track and field give us an opportunity to investigate the advantage of being born early in the year based upon actual performance, since objective criteria are the performance indicators. Hence, the aim of the present study was to investigate the occurrence of RAE in Norwegian track and field athletes in events where physical capacity is important for success. Methods All individual season best results from the register of The Norwegian Athletics Federation (n = 28 999) obtained in all competition classes from the age of 10 years to senior in both sexes on 60m and 600m from 2011 to 2020 were downloaded. One-way ANOVA and LSD post hoc analyses were used to analyze performance differences according to birth quartiles between athletes. Further, odds ratios (OR) were used to calculate the odds of being among the top-100 for athletes for those born in the first quartile of the year compared to the last. Results The RAE was present in several of the competition classes in sprint compared to middle-distance running, and in more male than female competition classes. Overall, the OR of being among the top-100 in one of the competition classes on 60m sprint when born in first quartile compared to last quartile was 2.88 [2.30–3.62] for males and 1.54 [1.26–1.89] for females. Conclusion Being born early in the year in events with high demand for specific physical capacities is an advantage in both sexes in most of the youngest competition classes. In males, the advantage of being born early in the year lasted longer in sprint than in middle-distance running, indicating that puberty affects performance in sprint and middle-distance running differently.
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The paper analyses two datasets of elite soccer players (top 1000 professionals and UEFA Under-19 Youth League). In both, we find a Relative Age Effect (RAE) for frequency, but not for value. That is, while there are more players born at the start of the competition year, their transfer values are no higher, nor are they given more game time. We use Poisson regression to derive a transparent index of the discrimination present in RAE. Also, because Poisson is valid for small frequency counts, it supports analysis at the disaggregated levels of country and club. From this, we conclude there are no paragon clubs or countries immune to RAE; that is clubs and countries do not differ systematically in the RAE they experience; also, that Poisson regression is a powerful and flexible method of analysing RAE data.
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Research question: This study investigates whether the relative age effect (RAE) persists in the long term and affects Italian-born footballers’ performance and wages. Research methods: A unique dataset on 1700 individual players’ remuneration and performance was collected and analysed through the chi-square goodness-of-fit, the Spearman’s rank correlation and an econometric model. Results and findings: This study contributes to the literature by providing clear results on long-term RAE. We find evidence of the RAE in terms of representativeness, which means that, in an age group, players born relatively early are over-represented, while those born relatively late are under-represented, even accounting for national birth trends. Moreover, although they perform similarly, the gross wages of players born relatively late are statistically significantly lower than those of players born relatively early. Implications: This situation needs to be considered by various football stakeholders and tackled accordingly to minimize the loss of potential youth football talent. Further research is needed to identify the determinants of RAE in the long term. The working paper version is available here: www.bbk.ac.uk/management/docs/workingpapers/WP9.pdf
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The relative age effect (RAE) describes an overrepresentation of players born early (Q1) in a selection year and is highly prevalent within youth sport pathways. However, a dearth of research has investigated the RAE at the “super-elite” level. The present research assessed the presence of RAE in super-elite performers. Study 1 investigated RAEs in the world’s best international Test cricketers (N = 262) over a 20-year period according to a robust and stringent “super-elite” criteria. Results revealed the RAE (Q1) when all disciplines were combined. Upon closer examination, this effect was also observed for the batting and spin bowling disciplines, whereas no RAE was found for the pace bowling discipline. Study 2 investigated RAEs in super-elite rugby union players (N = 691) over a 20 year period. Results revealed the RAE for backs (Q1) and a reversal of the traditional RAE (Q4) for forwards, and when all rugby union positions were combined. These findings provide new evidence of RAEs at the super-elite level and present both inter and intra sports differences. Potential explanations for these findings are explored, owing to the survival and evolution of the fittest concepts, and the implications for future research and applied practice are presented.
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The aim of this study was to identify the relative age effect (RAE) in young Polish male (n = 3849) and female (n = 3419) basketball players aged 14 to 22 years competing in the elite games of the Polish Youth championships. The distribution of birth dates, body height, players' match statistics, and the results of teams participating in championships were identified. The RAE was observed in male and female group, regardless of players age. Nevertheless, the greatest disproportion in the distribution of dates of birth was found in U16 group of boys (V = 0.25, p < 0.0001). Significant differences in body height were identified in U14 and U16 groups of boys (p < 0.0001) and U14 group of girls (p < 0.01). The RAE was the most detrimental in the group of boys from teams ranked 9th or lower (p < 0.0001). The groups of male and female basketball players from the top 3 teams had the highest average body height (p < 0.001). In U14 boys, significantly higher match results and performance index ratings (PIR) were observed for players born in the first half of a calendar year. The research results show the impact of the RAE on the success of youth basketball teams in Poland. The month of birth, body height and sex may determine sporting achievements in youth basketball. Coaches should consider the chronological age and pubertal growth acceleration (APHV-age at peak height velocity) of players to optimize the process of identifying gifted basketball players, especially among boys of 14 years of age. Key words: Basketball,
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Purpose: Relative Age Effect (RAE) is a bias usually observed in youth athletes and in academia, where participation is higher among those born early in the year. We aimed to determine RAE in undergraduate students of Sport Science. Methods: The birth dates of a sample of undergraduate students (N=11280) at University of Torino (Italy) were collected. Students belonged to Sport Science (N=5229) and other faculties (N=6051; Law, Arts, and Economics). All students were divided into four groups depending on their birth date, and the distribution of the birth dates was compared with the general population by means of chi-square test. Results: The observed distribution was different from expected for male undergradute students of Sport Science (P=0.009), where most students were born in the first months of the year. Diffently, in female students of Sport Science and students belonging to other faculties, the birth dates were more normally distributed (P>0.05). Conclusion: In conclusion, we observed a skewed distribution of the birth dates in male, but not in female, undergraduate students of Sport Science. Probably, the physical advantages of the young males born at year beginning may have oriented the choice of Sport Science degree, an academic field where physical capacities provide some advantages.
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AimsTo evaluate relative age effects (RAEs) in wrestlers at the junior world championships. Methods Data for wrestling athletes representing 77 different countries that participated in the junior (under 21 years of age) world championships between 2006 and 2014 were collected from a publically available source. RAEs were examined among 807 female freestyle, 1205 male freestyle, and 1202 male Greco-Roman wrestlers. Athletes were sub-categorized by weight class, as medalists, and according to the number of years active in wrestling. The observed frequency of athletes per birth quarter was compared to an even quarterly distribution using χ2 tests. ResultsNo RAEs were shown for female freestyle wrestlers. For male freestyle wrestlers, RAEs were found for the overall group, the medalists, all but the extra lightweights (under 50/55 kg), and both the least (<5 years active) and moderately (5–7 years active) experienced. For male Greco-Roman wrestlers, RAEs were shown for the overall group, the middle (under 74/84 kg) and heavy weights (under 96/120 kg), and only the moderately experienced (5–7 years active). Conclusions Despite weight categorization, junior male wrestlers are susceptible to RAEs; however, effects in the lightest and most experienced athletes may be diminished. Differences across weight categories appear to convey different trends between the male freestyle and Greco-Roman athletes. Thus, sporting organizations, training staff, and others interested in the welfare of athletes should consider the potential impact of RAEs in wrestling.
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Grouping people according to chronological age is popular in fields such as education and sport. Athletes who are born in the first months of the year usually have cognitive and physical development differences in contrast to those born in the last months of the same year. That is why competitive teams tend to select older players more often than youngsters. Age differences between athletes born in the same year as well as an over-representation of older players are known as the Relative Age Effect. This effect is extensively described in young and elite team sports such as basketball, volleyball or, ice-hockey, as well as in soccer. The purpose of this study is to examine the state-of-the-art of the Relative Age Effect in youth and elite soccer players. This review summarizes recent research articles on the Relative Age Effect related to competitive soccer from 2010 to 2016. The systematic literature search was conducted in four databases: SPORTDiscus, Medline, EBSCO host and Google Scholar. Although causes and final solutions have not been clearly achieved yet, it is necessary to continue investigating this phenomenon in order to provide a starting point for future research.
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This study examined the impact of relative age effect (RAE) on selection to the Spanish National Athletics Federation (RFEA) training camps (TC) between 2006 and 2013. Overall, 1,334 selected athletes at U15 years (cadet) and U17 years (juvenile) were compared against 27,711 licensed but unselected athletes for the same age groups. The results highlighted the influential role of the RAE on selection to national level track and field training camp opportunities. Interestingly, this effect was mediated by age and gender, where effects were stronger for both males and younger athletes (U15), with no evidence of RAE for older (U17) female athletes. These results support the “maturation-selection” hypothesis as a mechanism for RAE. Particularly given the long-term goals of RFEA (e.g., production of successful senior elite athletes), these results highlight the need to consider the impact of current selection processes on effective provision of opportunities to those athletes with most potential to succeed in the long term. A number of possible context-relevant solutions are discussed, including education and awareness raising, using holistic selection criteria and correction adjustments techniques. http://www.tandfonline.com/eprint/5NCM3ZR5vxjw6ju5VPse/full
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When placed into age groups for junior sporting competition, the relative differences in age between children leads to a bias in who is evaluated as being talented. While the impact of this relative age effect (RAE) is clear, until now there has been no evidence to show how to reduce it. The aim of this study was to determine whether the selection bias associated with the RAE could be reduced. Talent scouts from an elite football club watched junior games and ranked players on the basis of their potential. Scouts were allocated to one of three groups provided with contrasting information about the age of the players: (1) no age information, (2) players' birthdates or (3) knowledge that the numbers on the playing shirts corresponded to the relative age of the players. Results revealed a significant selection bias for the scouts in the no-age information group, and that bias remained when scouts knew the players' dates-of-birth. Strikingly though, the selection bias was eliminated when scouts watched the games knowing the shirt numbers corresponded to the relative ages of the players. The selection bias associated with the RAE can be reduced if information about age is presented appropriately.
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Few studies have investigated whether relative age effects (RAEs) exist in school sport. None have sought to test the competing maturational and social-agent hypotheses proposed to explain the RAE. We aimed to determine the presence of RAEs in multiple school sports and examine the contribution of maturational and social factors in commonplace school sports. We analyzed birth dates of n=10645 competitors (11-18 years) in the 2013 London Youth Games annual inter-school multisport competition and calculated odds ratio (OR) for students competing based on their yearly birth quarter (Q1-Q4). Multivariate logistic regression was used to determine the relative contribution of constituent year (Grade) and relative age in netball and football which used multiyear age groupings. In girls, RAEs were present in the team sports including hockey, netball, rugby union, cricket and volleyball but not football. In boys, RAEs were stronger in common team sports (football, basketball cricket) as well as athletics and rowing. In netball and football teams with players from two constituent years, birth quarter better-predicted selection than did constituent year. Relatively older players (Q1) from lower constituent years were overrepresented compared with players from Q3 and Q4 of the upper constituent years. RAEs are present in the many sports commonplace in English schools. Selection of relatively older players ahead of chronologically older students born later in the selection year suggests social agents contribute to RAEs in school sports.