Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   Original article    40 
ABSTRACT 
The aim of the present study was two-fold; (1) to 
examine the relative age effect of football players 
representing their countries and reaching the podium 
in the FIFA U17 and U20 World Cups between 2009 
and 2019, and (2) to analyze the relative age effect 
according to players’ positions. This study was a 
retrospective cross-sectional design. A total of 756 
male football players were included in the study. 
Dates of birth of football players were grouped into 
periods of three months in a quartile year. All data is 
presented in frequency and percentage. Chi-square 
was applied to determine differences in the inter-
group distributions. The odds ratio, confidence 
interval (95%) and Cramer’s V were calculated. The 
findings emphasized the relative age effect in 
successful national teams participating last six U17 
and U20 World Cup. The relative age effect of U17 
was higher compared to U20 (χ² = 70.974; p < 0.001, 
χ² = 39.587; p < 0.001 respectively). As a result of 
the research, players born in the first quartile of the 
year have been represented on podium more than 
those born in the last quartile, significantly. The 
findings of this study confirm the presence of 
relative age effect among football players reaching 
the podium in the last six U17 and U20 World Cup. 
Coaches and sports scientists are suggested to take 
the relative age effect into reconsideration to reduce 
this bias and to improve the system leading to loss of 
talents as a consequence. 
Keywords: talent identification, birth distribution, 
player selection, annual age grouping 
Department of Coaching Education, Faculty of 
Sport Sciences, Akdeniz University, Antalya, 
Turkey 
 
 
 
IZVLEČEK 
Pričujoča študija ima dva cilja: (1) preučiti vpliv 
starosti nogometašev, ki predstavljajo svoje države 
in dosegajo stopničke v FIFI U17 in svetovnih 
prvenstvih do 20 let med letoma 2009 in 2019, ter 
(2) analizirati vpliv starosti glede na položaje 
igralcev. V študijo smo vključili 756 nogometašev. 
Datume rojstev nogometašev smo razvrstili na 
četrtine lets. Za določitev razlik v porazdelitvah med 
skupinami smo uporabili hi-kvadrat test ter 
izračunali  razmerje verjetnosti, interval zaupanja 
(95%) in Cramerjev koeficient. Ugotovili smo, da 
ima starost vpliv na uspešnost reprezentanc, ki so 
uvrstile zadnjih šestih svetovnih prvenstev do 17 let 
in do 20 let. Relativni starostni učinek U17 je bil 
večji v primerjavi z U20 (χ² = 70,974; p <0,001, χ² = 
39,587; p <0,001). Igralci, rojeni v prvem kvartilu 
leta so dosegali značilno boljše rezultate kot tisti, 
rojeni v zadnjem kvartilu leta. Ugotovitve pričujoče 
študije potrjujejo prisotnost relativnega starostnega 
učinka pri nogometaših, ki so dosegli stopničke na 
zadnjih šestih svetovnih prvenstvih U17 in U20. 
Predlagamo, da trenerji in športni znanstveniki 
ponovno razmislijo o učinku vpliva starosti, z 
namenom zmanjšanja to pristranosti in izboljšanja 
sistema, ki lahko posledično izgubi talente. 
Ključne besede: identifikacija talentov, porazdelitev 
rojstev, izbira igralcev, letna starostna skupina 
Corresponding author*: Ali Işın,  
Department of Coaching Education, Faculty of Sport 
Sciences, Akdeniz University, Antalya 07058, 
Turkey  
E-mail: isin_ali@hotmail.com
Ali Işın THE RELATIVE AGE EFFECT IN SUCCESSFUL 
NATIONAL FOOTBALL TEAMS 
 
VPLIV STAROSTI NOGOMETAŠEV PRI 
USPEŠNIH NOGOMETNIH REPREZENTANCAH 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    41 
INTRODUCTION 
In any sports branch, some children are older than their peers. This is a phenomenon commonly 
known as the relative age effect (RAE) (Musch & Hay, 1999). RAE is affected by physical, 
cognitive, and physiological differences. Therefore, athletes born at the end of the year are 
expected to be systematically disadvantaged throughout childhood (Fumarco & Rossi, 2018). 
As a result of this, the tendency to select the relatively oldest football players in each category 
is called RAE (Gil et al., 2014).   
From the first stages of life, children are divided into chronological age groups. This grouping 
aims to provide equal opportunities for children. Similarly, athletes are divided into different 
game categories according to their chronological age in order to ensure equality in the 
competition and the same opportunities for success in young people (Musch & Grondin, 2001). 
For example, in 1997, Fédération Internationale de Football Association (FIFA) set the 
beginning of the selection year for football players in international tournaments and 
competitions as January 1. While applying this selection criterion, the primary purpose was to 
ensure that children have a fair chance of competition and equal success for all (Helsen, Van 
Winckel, & Williams, 2005). However, the classification of these categories does not seem 
sufficient due to the 12-month difference between the youngest and oldest athletes. Because 
significant anthropometric and physiological changes occur in children during adolescence 
(Augste & Lames, 2011), the athlete born in January will have a one-year advantage compared 
to his peer born in December (Arrieta, Torres-Unda, Gil, & Irazusta, 2016). However, as 
Williams pointed out, by the age of 17, most football players are expected to be close to the 
level of physical and psychological maturity. Thus, it is thought that the psychological and 
physical differences between the old and young players are reduced (Williams, 2010).   
Barnsley et al. (1985) researched RAE in Canadian professional ice hockey players and reported 
that 40% of players were born in the first quartile of the year (Barnsley, Thompson, & Barnsley, 
1985). From then, RAE has become a popular subject in the field of sports science (Wattie, 
Schorer, & Baker, 2015) and has been researched in many sports branches (Cobley, Baker, 
Wattie, & McKenna, 2009; Smith, Weir, Till, Romann, & Cobley, 2018) Although there are 
contradictory findings related to the presence of RAE, many studies reported an unequal 
distribution of birthdates among athletes in many sport branches, and those born in the first 
quartile of the same age group were selected more than their peers born in the last quartile 
(Helsen et al., 2005; Işın & Melekoğlu, 2020; Williams, 2010). However, RAE was not 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    42 
suggested in sports that did not require physical attributes such as golf and shooting sports 
(Smith et al., 2018). 
Studies investigating RAE in football have focused on professional male football players and 
youth players (Barnsley, Thompson, & Legault, 1992; Helsen et al., 2005; Salinero, Pérez, 
Burillo, & Lesma, 2013; Yagüe, de la Rubia, Sánchez-Molina, Maroto-Izquierdo, & Molinero, 
2018). However, these studies researched professional leagues and international tournaments 
and competitions of national teams (World cup, European cup, etc.) (Yagüe et al., 2018). 
Although RAE is a widely studied topic, studies have mostly focused on the effects of RAE in 
a single tournament or competition as an investigation of participation trends. Among football 
players born in the same year, relatively older players have better physical attributes (Malina et 
al., 2000) which directly or indirectly affect their performances positively (Arrieta et al., 2016). 
Given this aspect, it can be suggested that RAE may be more prominent among successful 
teams/players. Thus, success is another essential issue to consider the effect of this phenomenon 
since professional careers of athletes are built upon those career achievements. Therefore, it is 
insufficient to focus on only one tournament and participation trends in that specific 
tournament. A longitudinal approach is needed to present the real setting in football regarding 
RAE with additional tenets of elite sport like success. For this reason, the aim of this study was 
two-fold: (1) to investigate the relative age effect among football players reached the podium 
(Champion, runner-up, and third place) in the FIFA U17 and U20 World Cups between 2009-
2019, and (2) to analyze RAE among football players according to their positions. In accordance 
with the aims of this study and the relevant literature, it was hypothesized  that; 
1 - Significantly bias distribution among award-winning football players will be present in favor 
of those born in the first quartile. 
2 - A strong RAE will be present particularly among midfielders and defenders. 
3 - The RAE will exist throughout the years. 
 
METHODS 
Experimental Approach to the Problem 
This study examined the birthdates of the football players of the countries that were successful 
in the FIFA U17 and U20 World Cups from 2009 to 2019. Another aim was to analysis RAE 
of the football players according to their positions. As mentioned (Williams, 2010), the birth 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    43 
rate was assumed to be equal in all months (per month; %8.33, per quartile; %25.0). Birth dates 
of football players are grouped as a four-quartile year (Q); football players born in January, 
February and March included in the 1st quartile (Q1), football players born in April, May and 
June in the 2nd quartile (Q2), football players born in July, August and September in the 3rd 
quartile (Q3) and football players born in October, November, and December in the 4th quartile 
(Q4). Birth dates, name-surname, playing positions, and country information of the players 
from the official website of FIFA (www.fifa.com) were obtained. Football players were 
evaluated in four categories by their playing positions as reported in the squad list: goalkeeper 
(GK), defender (DF), midfielder (MF), and forward (FW). This study was retrospective cross-
sectional design and carried out according to the Declaration of Helsinki. This study was 
approved by the clinical research ethics committee (2020 / KAEK-230). 
Participants  
A total of 24 countries participated in each tournament, and each country reported 21 players 
(three of whom must be goalkeepers) in the squad list. The present study consisted of a total of 
756 male football player from the successful countries (champion, runner-up and third place) 
in the FIFA U17 and U20 World Cups between 2009-2019 were included in this study.  
Statistical analysis  
Since the cut-off date for football players is accepted as January 1 (González-Víllora, Pastor-
Vicedo, & Cordente, 2015), January was accepted as the first month and December as the last 
month for all statistical analysis. All data used in the study are presented in frequency and 
percentage (%). SPSS 23.0 and Windows Office Excel were used for statistics. The statistical 
significance value was accepted as p < 0.05, p < 0.01 and p < 0.001.  
For the observed and theoretically expected differences among the distribution of birth dates, 
chi-square (χ2) tests were used. Cramer's V was used to determine the effect size. According to 
Cramer (2016), the effect sizes are divided into 3 as small effect (V = 0.06-0.17), medium effect 
(V = 0.18 - 0.29) and large effect (V = 0.30). The Odds ratio and confidence interval (%95) 
were calculated to determine the comparisons of Q1 vs. Q4, Q2 vs. Q4, and Q3 vs. Q4.  
 
  

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    44 
RESULTS 
In this study, birth month distributions of 756 male football players were analyzed. There was 
an obvious relative age effect in each year both in U17 and U20 World Cup (χ² = 70.974; p < 
0.001, χ² = 39.587; p < 0.001, respectively). For all player groups, the number of football players 
born in Q1 (40.6%) was higher than the number of football players born in Q4 (16.9%) 
(OR=2.40; 95% CI 1.80-3.20). The effect size observed of the RAE in U17 World Cup noted 
large in the case of 2011, 2017, and 2019 medium in the case of 2009 and 2015 and small in 
the case of 2013. The effect size of observed of the RAE in U20 World Cup noted large in the 
case of 2019, medium in the case of 2011, 2015 and 2017 and small in the case of 2009 and 
2013. A significant difference was found among Q1 vs. Q4 and Q2 vs. Q4 for the entire cohort 
of players (χ² = 107.799; p < 0.001). It was determined that football players born in Q1 in the 
U17 and U20 World Cup s have nearly 2.50 times more chances to be selected compared to 
those born in Q4. Football players born in Q1 in the last U17 vs. U20 World Cup s were selected 
more than those born in Q4 (Table 1.).  
According to the playing positions of football players, football players under 17 showed a 
significant difference in the birth-date distribution for DF, MF, and FW (χ² = 38.552; p < 0.001, 
χ² = 26.200; p < 0.001,  χ² = 9.636; p < 0.05., respectively); whereas football players under 20 
showed a significant difference for MF and FW (χ² = 23.474; p < 0.001, χ² = 10.900; p < 0.05., 
respectively) (Table 2.). 
Figure 1. The percent of age distribution (by month) of successful national teams' football 
players at last six U17 and U20 FIFA World Cup. 
 
0
5
10
15
20
25
Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec
U17 U20 Entire cohort

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    45 
Table 1. The birth month distribution of the football players, chi-square (χ²), Cramer's V and 
Odds ratio comparisons (95% confidence interval). 
 
 
Quartile of birth   Odds ratio (CI 95%) 
 
Q 1  
(n; %) 
Q 2 
(n; %) 
Q 3 
 (n; %) 
Q 4 
 (n; %) 
χ² V Q 1-Q 4 Q 2-Q 4 Q 3-Q 4 
U17 
2009 
(n:63) 
27 
(42.9) 
9 
(14.3) 
9 
(14.3) 
18 
(28.6) 
14.143
b
  0.27 
1.50 
(0.60-3.76) 
0.50  
(0.17-1.45) 
0.50  
(0.17-1.45) 
2011 
(n:63) 
30 
(47.6) 
17 
(27.0) 
10 
(15.9) 
6 
(9.5) 
21.127
c
 0.33 
5.00 
(1.63-15.34) 
2.83  
(0.88-9.07) 
1.67 
(0.49-5.70) 
2013 
(n:63) 
23 
(36.5) 
15 
(23.8) 
14 
(22.2) 
11 
(17.5) 
5.000 0.16 
2.09 
(0.77-5.70) 
1.36  
(0.48-3.88) 
1.27  
(0.44-3.65) 
2015 
(n:63) 
23 
(36.5) 
19 
(30.2) 
5 
(7.9) 
16 
(25.4) 
11.349
a
 0.25 
1.44 
(0.56-3.70) 
1.19  
(0.45-3.12) 
0.31  
(0.09-1.06) 
2017 
(n:63) 
31 
(49.2) 
12 
(19.0) 
13 
(20.6) 
7 
(11.1) 
21.000
c
 0.33 
4.43 
(1.51-13.01) 
1.71  
(0.53-5.49) 
1.86  
(0.59-5.89) 
2019 
(n:63) 
29 
(46.0) 
17 
(27.0) 
12 
(19.0) 
5 
(7.9) 
19.476
c
 0.32 
5.80 
(1.79-18.84) 
3.40  
(1.01-11.49) 
2.40  
(0.68-8.42) 
All 
(n:378) 
163 
(43.1) 
89 
(23.5) 
63 
(16.7) 
63 
(16.7) 
70.974
c
 0.25 
2.59 
(1.72-3.89) 
1.41  
(0.92-2.17) 
1.00  
(0.64-1.57) 
U20 
2009 
(n:63) 
21 
(33.3) 
15 
(23.3) 
10 
(15.9) 
17 
(27.0) 
3.984 0.15 
1.24  
(0.48-3.18) 
0.88  
(0.33-2.36) 
0.59  
(0.21-1.68) 
2011 
(n:63) 
18 
(28.6) 
22 
(34.9) 
16 
(25.4) 
7 
(11.1) 
7,667 0.21 
2.57  
(0.84-7.87) 
3.14  
(1.05-9.45) 
2.29  
(0.74-7.08) 
2013 
(n:63) 
23 
(36.5) 
12 
(19.0) 
13 
(20.6) 
15 
(23.8) 
4.746 0.16 
1.53  
(0.59-3.98) 
0.80  
(0.29-2.24) 
0.87  
(0.31-2.40) 
2015 
(n:63) 
28 
(44.4) 
16 
(25.4) 
12 
(19.0) 
7 
(11.1) 
15.286
b
 0.28 
4.00  
(1.35-11.82) 
2.29  
(0.74-7.08) 
1.71  
(0.53-5.33) 
2017 
(n:63) 
24 
(38.1) 
15 
(23.8) 
11 
(17.5) 
13 
(20.6) 
6.270 0.18 
1.85  
(0.70-4.88) 
1.15  
(0.42-3.20) 
0.85  
(0.29-2.45) 
2019 
(n:63) 
30 
(47.6) 
15 
(23.8) 
12 
(19.0) 
6 
(9.5) 
19.857
c
 0.32 
5.00  
(1.63-15.34) 
2.50  
(0.77-8.11) 
2.00  
(0.60-6.66) 
All 
(n:378) 
144 
(38.1) 
95 
(25.1) 
74 
(19.6) 
65 
(17.2) 
39.587
c
 0.19 
2.22  
(1.47-3.33) 
1.46  
(0.96-2.24) 
1.14  
(0.73-1.77) 
 Entire 
cohort 
(n:756) 
307 
(40.6) 
184 
(24.3) 
137 
(18.1) 
128 
(16.9) 
107.799
c
 0.22 
2.40  
(1.80-3.20) 
1.44  
(1.06-1.95) 
1.07  
(0.78-1.47) 
Q1: January-March, Q2: April-June, Q3: July-September, Q4: October-December, V: effect size; small effect: V = 0.06 - 0.17, medium effect: V = 0.18 - 0.29, large effect: 
V ≥ 0.30, χ²: chi square, Significant difference 
a 
(p < 0.05),
 b 
(p < 0.01),
 c 
(p < 0.001) 
 
Table 2. The birth month distribution of the football players' playing positions, chi-square (χ²), 
Cramer's V and Odds ratio comparisons (95% confidence interval). 
 
 
Quartile of birth   Odds ratio (CI 95%) 
 
Q 1  
(n; %) 
Q 2 
(n; %) 
Q 3 
 (n; %) 
Q 4 
 (n; %) 
χ² V Q 1-Q 4 Q 2-Q 4 Q 3-Q 4 
U17 
GK 
(n:54) 
21 
(38.9) 
13 
(24.1) 
8 
(14.8) 
12 
(22.2) 
6.593 0.20 
1.75 
(0.62-4.93) 
1.08  
(0.36-3.22) 
0.67  
(0.21-2.15) 
DF 
(n:116) 
57 
(49.1) 
26 
(22.4) 
14 
(12.1) 
19 
(16.4) 
38.552
c
 0.33 
3.00 
(1.44-6.23) 
1.37  
(0.62-3.00) 
0.74 
(0.31-1.74) 
MF 
(n:120) 
52 
(43.3) 
27 
(22.5) 
28 
(23.3) 
13 
(10.8) 
26.200
c
 0.27 
4.00 
(1.81-8.82) 
2.08 
(0.90-4.78) 
2.15  
(0.94-4.94) 
FW 
(n:88) 
33 
(37.5) 
23 
(26.1) 
13 
(14.8) 
19 
(21.6) 
9.636
a
 0.19 
1.74 
(0.77-3.93) 
1.21 
(0.52-2.83) 
0.68  
(0.27-1.72) 
U20 
GK 
(n:54) 
22 
(40.7) 
13 
(24.1) 
9 
(16.7) 
10 
(18.5) 
7.778 0.22 
2.20 
(0.76-6.36) 
1.30  
(0.43-3.97) 
0.90  
(0.28-2.91) 
DF 
(n:114) 
40 
(30.8) 
36 
(27.7) 
33 
(25.4) 
21 
(16.2) 
6.185 0.13 
1.90 
(0.91-3.99) 
1.71 
(0.81-3.46) 
1.57 
(0.74-3.34) 
MF 
(n:130) 
50 
(43.9) 
27 
(23.7) 
20 
(17.5) 
17 
(14.9) 
23.474
c
 0.25 
2.94 
(1.41-6.13) 
1.59  
(0.73-3.50) 
1.18  
(0.52-2.64) 
FW 
(n:80) 
32 
(40.0) 
19 
(23.8) 
12 
(15.0) 
17 
(21.3) 
10.900
a
 0.21 
1.88 
(0.80-4.42) 
1.12  
(0.45-2.75) 
0.71  
(0.27-1.85) 
Q1: January-March, Q2: April-June, Q3: July-September, Q4: October-December, V: effect size; small effect: V = 0.06 - 0.17, medium effect: V = 0.18 - 0.29, large 
effect: V ≥ 0.30, χ²: chi square, GK: goalkeeper, DF: defender, MF: midfielder, FW: forward, Significant difference 
a 
(p < 0.05),
 b 
(p < 0.01),
 c 
(p < 0.001) 
 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    46 
DISCUSSION 
The aim of this study to analyze if RAE exists in the FIFA U17 and U20 World Cup 
competitions. In accordance with this purpose, the birth dates of the football players of the 
countries that were successful in the FIFA U17 and U20 World Cups from 2009 to 2019 were 
examined.  
Most of the studies focused on RAE in football have determined that players born in the first 
months of the year are more successful in this sport (Augste & Lames, 2011). For this reason, 
clubs in more prestigious or higher leagues have selected the football player considering the 
RAE (González-Víllora et al., 2015). The most important reason for this is that there is a 12-
month difference between the player born in January and born in December within the same 
calendar year. Because relatively younger players in age cohort will have a positive advantage 
with regard to physical, physiological and psychological development compared to the 
relatively smaller (i.e., born at the end of selection year) peer (Vaeyens, Philippaerts, & Malina, 
2005). In this context, it is seen that maturity is one of the most determining factors in the 
selection process of football players (Práxedes, Moreno, García-González, Pizarro, & Del 
Villar, 2017). 
The present study stated an unequal birth month distribution among football players. The birth 
month's distribution was higher in favor of football players born in the first months of the year, 
for all competitions. In other words, the number of those born in Q1 is more than the number of 
those born in Q4. For all football players in under 17 and 20, 40.6 % were born in Q 1, while 
only 16.9% were born in Q4. Similarly, Williams (2010) was determined that 40% of the 
countries participating in the U17 World Cup between 1997-2007 were composed of football 
players born in Q1, and only 16% were selected from those born in Q4 (Williams, 2010). 
Simmons and Paull (2001) emphasized that none of the 59 players in the Swedish football team 
under 17 were born in the last two months of the selection year. Unlike these results, 39 (66%) 
players were born in Q1 (Simmons & Paull, 2001). Helsen et al. (2005) reported that for almost 
all countries participating in the Youth European Cup, those born in the Q1 were more than 
those born in Q4. These results may be an indication that coaches tend to select football players 
born in Q1. Since only successful national teams are evaluated in this study, it is not possible to 
comment for the last six U17 and U20 World Cup s. However, as stated in previous studies 
(Helsen et al., 2005; Williams, 2010), the rate of relative age effect is high in youth tournaments. 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    47 
It may explain the relative age effect of successful teams, as there are similar results in the last 
six tournaments. 
The relationship between RAE and success has been investigated in limited number of research. 
Ford and Williams (2011) investigated relationship between RAE and success in male 
professional team sports (football, baseball, ice hockey, and Australian football), and reported 
no distribution bias for relatively older or younger players. However, Ferriz-Valero et al. (2020) 
presented a strong RAE among medal owners in Valencian Triathlon League between 2012 and 
2016 in favor of early born athletes. Similarly, Bilgiç and Devrilmez (2021) noted a strong RAE 
among European badminton players reaching the podium in U15, U17 and U19 continental 
championships in favor of those born in Q1. Those aforementioned results might seem 
incompatible with each other, the nature and characteristics demands of sports regarding team 
and individual are better to be taken into consideration. Although Ford and Williams (2011) 
reported contrary results, our findings confirm the presence of RAE in a team sport which calls 
for further research in the field. 
There are several possible theories about observing the RAE in youth football players. First, 
relatively older players in age cohorts are expected to be better physical performances and more 
physically mature than their younger counterparts. Studies in Canadian hockey players as well 
as Portuguese and Mexican football players show that skeletal maturity may play a significant 
role in the selection process of football players (Malina, Meleski, & Shoup, 1982; Malina et al., 
2000).  Gill et al. (2014) stated a significant relationship between the anthropometric and 
physical performances of young football players and their chronological ages. Those born in 
the first quartile were taller than their peers born in the other quartile. Moreover, those born in 
Q1 performed better in the physical tests (velocity and agility) (Gil et al., 2014). Carling et al. 
(2009)  reported that football players born in Q1 performed better than their peers born in the 
following quartiles, but there was no significant difference in any of their fitness levels In the 
light of these results, these differences in physical performance in favor of those born in the 
first quartile of the year increase their chances of being selected. It will cause the coaches, who 
want to benefit from these differences positively, to tend to select football players born in Q1. 
Another theory is that the players born at the beginning of the selection year are seen to be more 
talented by coaches. This allows them to be transferred to elite teams and, as a result, to receive 
higher quality coaching (Helsen, Starkes, & Van Winckel, 1998; Jiménez & Pain, 2008). Helsen 
et al. (1998) reported that football players who were born at the end of the year from the age of 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    48 
12 tent to drop-out of football more. Nevertheless, Jimenez & Pain (2008). have thought that 
the RAE will lead to negative processes in the selection of athletes. They reported that compared 
to his peers born earlier in the same selection year, the chances of being selected, although they 
were more talented as athletes, being born in the last quartile of the year were low, resulting in 
potential talented players dropping-out of sports.  
Another aim of this study was to research the RAE of football players according to their 
positions. This present study observed RAE for all positions except GK for U17. RAE found in 
MF and FW for U20. Salinero et al. (2013) researched RAE by positions in England, Spain, 
Italy, France and Germany professional football. MF was the one most affected by RAE. 
Among the top five leagues, RAE was not observed only in the Premier league' midfielders. 
The second position most influenced by RAE in European leagues was DF and existed in 
England, Italy, and Spain. RAE in FW only appeared in England. Hurley et al. (2019) found 
that among the international athletes, RAE was observed in DF and MF, whereas USA athletes 
showed RAE for MF and GK. Del Campo et al. (2010) stated that playing position did not have 
any effect on RAE.  Based on all these results, the relationship between playing positions and 
RAE could not be found clearly. This may be because teams select players for their game plans 
and strategy, because it can be expected that this effect will be higher in goalkeepers and 
defenders where physical characteristics predominate, and this effect will be less in midfielders 
where technique is at the forefront.  However, as a result of this study, the existence of RAE in 
the selection of midfielders in both age groups supports the idea that teams selected players 
according to their game strategies. 
Limitations of the study 
There are certain limitations of this study. Firstly, all the data analyzed in the research were 
obtained from the official website of FIFA. Although it is considered the most reliable source, 
certain limitations regarding data should be considered accordingly. Anthropometric and 
performance-related data were not analyzed and related within the concept of RAE due to 
limited data source. Further studies are needed to consider those variables to reach a broader 
conceptualization and understanding of RAE from different tenets of sport performance.  
Furthermore, only football players reaching the podium in the last six FIFA U17 and U20 World 
Cups between 2009-2019 were included in this study. Thus, further research is better to consider 
a broader period of time for both youth and adult categories.  
 

Kinesiologia Slovenica, 27, 2, 40-51 (2021), ISSN 1318-2269   The relative age effect in football    49 
CONCLUSION 
The present study revealed a strong relative age effect in the last six World Cups. In both the 
U17 and U20 World Cups, the number of football players born in Q1 was higher than the 
number of football players born in Q4. It can be thought that coaches would have chosen this 
direction in order to benefit from the physical superiority of those born earlier in the same 
selection year. Considering that those born in Q1 U17 have more chances to be selected, the 
same effect is expected to continue in the U20. This is because unselected players tended to 
drop-out football. Therefore, the fact that more athletes are active in the first quartile leads to 
the selection of more athletes than the first quartile. This will result in successful clubs having 
more players in the first quartile. However, in this study, the relative age effect of U20 World 
Cup decreased compared to U19 World Cup. The reason for this may be that physical 
differences decrease with maturation. Because coaches now focus on skills rather than physical 
attributes. 
Practical Implications 
 Coaches and sports scientists should be aware of the relative age effect and attempt to 
reduce this effect. 
 Talent is as important as physical attributes. Considering that physical differences 
decrease with maturation, coaches should pay attention to the period of time instead of 
a point in time while considering talent. 
 In younger age groups where physical differences are clearer, tournaments can be 
designed to cover two different age groups (1st group: January-June; 2nd group: July-
December). In this case, both the advantages of more advanced physical attributed are 
eliminated, and the development of talented athletes can be followed. 
 Finally, talent selection is very important at the U17 level. Players who are not selected 
in this age group usually drop out football. In this case, it leads to double advantages to 
athletes in the first quartile as being selected for the U20 national teams too. 
 
Declaration of Conflicting Interests 
The author(s) declared no potential conflicts of interest with respect to the research, authorship, 
and/or publication of this article. 
 

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