Materials : Coaching

The Relative Age Effect of Male and Female
Japanese National Soccer Players
Shigeki Matsuda* and Hiroaki Ishigaki***Faculty of Education, Shiga University
2-5-1, Hiratsu, Otsu, Shiga, 520-0862, Japanmatsuda@edu.shiga-u.ac.jp**Department of Education, The University of Tokyo[Received January 31, 2024; Accepted July 12, 2024]

The relative age effect (RAE) of Japanese national soccer players has not been examined to date.
The purpose of this study was to examine the RAE of male and female Japanese national soccer
players, targeting players who were called up to the Japanese national team from 2014 to 2020. The
subjects were 241 national soccer players (143 male and 98 female). Even if they were called up tonational team more than once, they were counted as one person. Among the Japanese male nationalsoccer players, Q1 (January to March) was 31.5%, Q2 (April to June) was 22.4%, Q3 (July to
September) was 20.3%, and Q4 (October to December) was 25.9%. As a result of the goodness-of-fit
test, no significant difference was observed in the proportions of Q1 to Q4. Q1/Q4 was 1.22, and S1/S2 was 1.17. Among female national soccer players, Q1, Q2, Q3, and Q4 were 20.4%, 28.6%, 27.6%,
and 23.5% respectively. No significant difference was observed in the proportions of Q1 to Q4. Q1/
Q4 was 0.87, and S1/S2 was 0.96. We concluded that there is no RAE for Japanese national soccer
players, whether men or women. Since the number of subjects is insufficient, it will be necessary toreturn to the analysis of the RAE of Japanese national soccer players in the future.
Keywords: birthday, football, Japan[Football Science Vol. 21, 13-20, 2024]

1. BackgroundChildren born in months far from the cutoff datehave been reported to be disadvantaged in academic
and sports activities (Cobley et al., 2009; Smith etal., 2018; Katsumata et al., 2018; Delorme et al.,2011; Till et al., 2010; Müller et al., 2015), and this iscalled the “relative age effect.” The relative age effectof soccer players has also been investigated manytimes, and the analyses have been conducted fromvarious aspects such as country, gender, position, andleague (Musch and Hay, 1999; Sedano et al., 2015;
Figueiredo et al., 2021; Yagüe et al., 2018; Brustio
et al., 2018). Among the previous studies regarding
the relative age effect of soccer players, the relative
age effect of national representative players has also
been investigated (Figueiredo et al., 2021; Götze andHoppe, 2020). For example, no relative age effectwas observed for either men or women in Portugal's
national A team (2016/2017 season to 2019/2020)(Figueiredo et al., 2021). In contrast, among women,
the percentage of soccer players who are close to theFootball Science Vol. 21, 13-20, 2024
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cutoff date is as low as 10.5%. In addition, in a study
that investigated Germany's representative soccer
players, the odds ratio was high for men than for
women, but no relative age effect was observed forboth men and women (Götze and Hoppe, 2020). Since
there are not many representative players from eachcountry, there may be a limitation of the research that
it is difficult to show statistical differences in eachstudy. In addition, the relative age effect of soccer
players who participated in the World Cup, in which
national representative players participate, has been
investigated (Pedersen et al., 2022). As a result, there
was no relative age effect until 2010, but a relative
age effect was observed in 2014 and 2018 World Cup
players for men. For women, no relative age effectwas observed consistently in the 2007–2019 World
Cup. Judging from these results, it may be that therelative age effect is beginning to become clear for
male national team players. In any case, it is thoughtthat the trend in the relative age effect of nationalteam players will also change, so the relative age
effect of national team players will continue to be an
13

Matsuda, S. et al.

important theme in the future.
In Japan, the relative age effect has been
investigated in professional male soccer players,
youth players, and professional female soccer
players (Nakata and Sakamoto, 2011; Sasano et al.,2020; Nakata and Sakamoto, 2012; Hirose, 2009;
Matsuda and Ishigaki, 2023A, 2023B). The relative
age effect of male professional soccer players has
been observed for some time (Nakata and Sakamoto,2011; Uchiyama, 1996), and a relative age effecthas also been observed in male professional soccer
players in recent years (Sasano et al., 2020; Matsuda
and Ishigaki, 2023B). However, in women, although
no relative age effect was observed in the top-level
female soccer players in Japan in 2010 (Nakata andSakamoto, 2012), a recent study did find a relative
age effect (Matsuda and Ishigaki, 2023A). Thus, therelative age effect of Japan's top-level soccer players
has been investigated, but the relative age effectof Japanese national soccer players has not beenclarified. As mentioned above, the relative age effectof national soccer players has been studied in othercountries, and to clarify the details of the relative
age effect of Japanese soccer players, it is necessary
to investigate the relative age effect of nationalsoccer players in Japan as well. A slightly older
study reported that the relative age effect of male
professional soccer players in Japan was clearer thanthat of German, Brazilian, and Australian professionalsoccer players (Musch and Hay, 1999). Therefore,
the tendency of the relative age effect of the Japanesenational soccer players may differ from that of othercountries. The elucidation of the relative age effectof Japanese national team players will provide useful
information for soccer coaches, parents of young
soccer players, and the players themselves, and will
also result in a comprehensive understanding of therelative age effect and the development of research inthis field.
In this study, based on the data of players who
were called up to the Japanese national team from2014 to 2020, we will clarify the relative age effectof male and female Japanese national soccer players.
In addition, to clarify the details of the relative age
effect, we will also examine the gender and positional
differences in the relative age effect.

14

2. Method
2.1. Subjects
The subjects were 241 Japanese national soccer
players (143 male and 98 female) who were called
up to international tournaments and official matchesfrom 2014 to 2020. Even if a player is called up tonational team more than once, they are counted as one
player. By position, there were 11 GK (Goalkeeper),
52 DF (Defender), 43 MF (Midfielder), and 37 FW(Forward) among the men and 10 GK, 32 DF, 36 MF,
and 21 FW among the women.

2.2. Data Collection
The date of birth of the subjects was obtained fromthe official website of the Japan Football Association(https://www.jfa.jp/). As these data are a matter ofpublic record, there was no need for informed consent
from subjects. The data-collection period was from
August 2021 to September 2021.

2.3. Statistical analysis
We calculated the number and percentage ofsubjects for each month based on their date of birth.
As in the previous study (Musch and Hay, 1999), we
calculated the Spearman rank correlation coefficientand determined the significance of establishing therelationship between the frequency of each birth
month and the number of participants born in eachmonth. Because the school year begins in April inJapan, April was taken as month 1 in this analysis.
Following previous studies (Nakata and Sakamoto,2011; Sasano et al., 2020), the date of birth of
the subjects was classified into 4 groups: the firstquarter (April–June; Q1), the second quarter(July–September; Q2), the third quarter (October–
December; Q3), and the 4th quarter (January–March;Q4), and we calculated the frequency and ratio in
each quarter. Additionally, we tested the goodnessof fit to examine the difference in the proportions of
Q1 to Q4. The expected value was calculated basedon the birth month distribution of Japanese people atbirth from a demographic survey conducted by the
Ministry of Health, Labour and Welfare of Japan.
Since the subjects' dates of birth ranged from 1978 to
2003, the birth months of children born between 1978
and 2003 were referenced. As a result, Q1 was 24.2%,
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RAE in Japanese National Soccer Players

Q2 was 24.8%, Q3 was 26.3%, and Q4 was 24.7%.
ω was calculated as the effect size. Effect sizes ω areconsidered to be small, moderate, and large, when ω
is 0.10, 0.30, and 0.50, respectively (Cohen, 1988).
Following previous research (Sasano et al., 2020), we
calculated Q1/Q4 to examine the difference between
the ratios of Q1 and Q4. In addition, S1/S2 was
calculated to examine the difference between the sumof the proportions of Q1 and Q2 (S1) and the sumof the proportions of Q3 and Q4 (S2). An χ2 test was
performed to examine gender differences and playing
positional differences in the proportions of Q1–Q4.
We used the Statistical Package for the Social
Sciences (SPSS, Version 27, IBM Corp.) and jsSTAR for statistical analysis, and we set the statisticalsignificance at 5%.

3. Results
No significant correlation was observed between

the birth months of the Japanese national male soccer
players and the frequency of each month (Table 1),
and Figure 1 shows this result. Among Japanese malesoccer players (overall), 31.5% in Q1, 22.4% in Q2,
20.3% in Q3, and 25.9% in Q4 (Figure 2). As a resultof the goodness-of-fit test, no significant difference
was observed in the ratios of Q1 to Q4 (Figure 2,
Table 2). Q1/Q4 was 1.22 and S1/S2 was 1.17 (Table
2). As a result of testing the goodness of fit for eachposition, no significant difference was observed forany position (Table 2).
No significant correlation was observed between
the birth month of the Japanese national female
soccer players and the frequency of each month(Table 1), and Figure 1 shows this result. Female
national soccer players (overall) were 20.4% in
Q1, 28.6% in Q2, 27.6% in Q3, and 23.5% in Q4(Figure 3). As a result of the goodness-of-fit test, nosignificant difference was observed in the ratios of Q1
to Q4 (Table 2). Q1/Q4 was 0.87 and S1/S2 was 0.96

Table 1 Distributions of players’ birth months and the results of correlation analysis

April

May

June

July

August September October November December January February March

Sum

13

17

16

13

12

7

10

11

8

12

12

12

143 -0.56 0.06

% 9.1

11.9

11.2

9.1

8.4

4.9

7.0

7.7

5.6

8.4

8.4

8.4

100.0

6

10

4

13

5

10

10

8

9

12

2

9

98

% 6.1

10.2

4.1

13.3

5.1

10.2

10.2

8.2

9.2

12.2

2.0

9.2

100.0

June

July

AugustSeptember

OctoberNovember December

January

February

Male

FemaleMale nFemale nrp-0.01 0.97

(%)
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0

April

May

March

Figure 1 R atio of players’ birth months in each month
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15

Matsuda, S. et al.

（%）χ2 = 5.511
p = 0.138

35
31.5
30

25.9
25

22.4
20.3

20
15
10
5
0

Q1
(Apr. - Jun.)

Q2(Jul. - Sep.)

Q3(Oct. - Dec.)

Q4(Jan. - Mar.)

Figure 2 R atio of players’ birth months in each quarter (Q1–Q4) in Japanese male nationalsoccer players(Table 2). As a result of testing the goodness of fit foreach position, no significant difference was observed
for any position (Table 2).
Regarding the ratio of Q1–Q4, we tested thepositional and gender differences, but no significant
differences were observed (sex difference: χ2 = 4.992,
p = 0.172, positional difference: male χ2 = 8.132, p =0.521, female χ2 = 10.000, p = 0.350).

4. Discussion
Overall, no relative age effect was observed in
the Japanese national soccer players for either men
or women. In comparison, no relative age effectwas observed for either men or women in Portugal's
national team players (2016/2017 season–2019/2020
national team players) (Figueiredo et al., 2021). In
this study (Figueiredo et al., 2021), players' birthdays
were divided into four periods (Q1: January to March,
Q2: April to June, Q3: July to September, and Q4:
October to December). For women, the number ofplayers who are close to the cutoff date (i.e. Q1) is
low at 10.5% in this previous study (Figueiredo etal., 2021). In addition, in a study that investigatedGermany's national team (players registered for theWorld Cup and Champions League since 2015),
no relative age effect was observed for either men
16

or women (although the odds ratio was higher formen than for women) (Götze and Hoppe, 2020).
The number of subjects in both studies was small;therefore, a simple interpretation is not possible, but
our results were found to be consistent with theseprevious studies. However, in the Spanish women's
national team (2010–2013), a relative age effect wasobserved, and the percentage of players near thecutoff date (Q1) was high at 34.5%. However, since
this previous study included not only seniors but also
U17, U19, and U21 players, it cannot be said that it is
the result of the representative players (Sedano et al.,2015). A previous study (Pedersen et al., 2022) thatanalyzed players who participated in the 2006–2018
World Cup did not show a relative age effect until
2014 in men, but a relative age effect was found in2014 and 2018. For women, no relative age effectwas observed between 2007 and 2019. Pedersen etal. (2022) assessed several players who participatedin the World Cup. In Pedersen et al.'s (2022) study,
the number of participants was approximately 730
men and 330–550 women in each World Cup, and thelarge number of participants increased the possibilityof detecting statistical differences. However, thenumber of participants in the present study was small,with 143 men and 98 women. Previous studies that
included few participants did not show a clear relative
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RAE in Japanese National Soccer Players

Table 2 Distribution of players in Q1–Q4, the result of χ2 test, Q1/Q4, and S1/S2

Q1
Q2
Q3
Q4
(Apr. - Jun.) (Jul. - Sep.) (Oct. - Dec.) (Jan. - Mar.)
Male

FW

Sum

χ2

p

ω

0.675

0.879

0.14

1.22

1.06

4.065

0.255

0.31

2.00

1.39

1.557

0.669

0.17

1.07

1.17

7.097

0.069

0.80

0.50

0.83

5.511

0.138

0.20

1.22

1.17

2.663

0.447

0.36

0.75

1.10

2.524

0.471

0.26

0.80

1.25

3.373

0.338

0.32

0.70

0.52

4.188

0.242

0.65

-

1.50

1.263

0.738

0.11

0.87

0.96

n

11

8

9

9

37

(%)

29.7

21.6

24.3

24.3

100.0

n

16

9

10

8

43

(%)

37.2

20.9

23.3

18.6

100.0

n

15

13

10

14

52

(%)

28.8

25.0

19.2

26.9

100.0

n

3

2

0

6

11

(%)

27.3

18.2

0.0

54.5

100.0

Total n

45

32

29

37

143

(%)

31.5

22.4

20.3

25.9

100.0

n

3

8

6

4

21

(%)

14.3

38.1

28.6

19.0

100.0

n

8

12

6

10

36

(%)

22.2

33.3

16.7

27.8

100.0

n

7

4

11

10

32

(%)

21.9

12.5

34.4

31.3

100.0

n

2

4

4

0

10

(%)

20.0

40.0

40.0

0.0

100.0

Total n

20

28

27

23

98

(%)

20.4

28.6

27.6

23.5

100.0

MF
DF
GK

Female FW
MFDFGKage effect (Figueiredo et al., 2021; Götze and Hoppe,
2020). For example, Figueiredo et al. (2021) analyzed
the relative age effect in Portugal among 61 men
and 57 women. Similarly, Götze and Hoppe (2020)
evaluated this effect among 46 men and womenin Germany’s national team. Studies focusing on
national players from a single country, such as thisstudy, tend to have fewer participants; therefore, theresults of this study differ from those of Pedersen etal.’s (2022) research on players who participated in
the World Cup.
A relative age effect for Japanese professional
male soccer players was found in 1993 season
data (Uchiyama, 1996) and also in a recent study
analyzing the 2018 season (Sasano et al., 2020).
The value of Q1/Q4 has also been investigated in a
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Q1vsQ4 S1vsS2

previous study and it was 2.2 in the 1993 data and2.1 in 2018 (Sasano et al., 2020). Since the Q1/Q4
ratio of this result was 1.22, it can be inferred thatthe tendency of the birth month distribution of therepresentative players is somewhat different from thatof the male professional soccer players as a whole.
A representative player is an excellent player chosenfrom the pool of professional soccer players. As forthe percentage of professional soccer players, thenumber of players whose birth month is far from thecutoff date (Q4) is small, but many excellent players
are thought to be among them. A study analyzing
English professional football club players found that
few academy players had birthdays far from the cutoff
date, but the probability of becoming a professionalsoccer player is reported to be higher for players
17Matsuda, S. et al.

（%）χ2 = 1.263
p = 0.738

35
30

28.6

27.6

25
20

23.5
20.4

15
10
5
0

Q1
(Apr. - Jun.)

Q2(Jul. - Sep.)

Q3(Oct. - Dec.)

Q4(Jan. - Mar.)

Figure 3 R atio of players’ birth months in each quarter (Q1–Q4) in Japanese female
national soccer players

whose birth months are farther from the cutoff (Kelly
et al., 2020). In other words, there are thought to be
excellent athletes among those whose birth monthis far from the cutoff date, so it is thought that thetendency of the relative age effect will be smaller inthe case of representative soccer players. However,looking at the results for the Japanese male nationalsoccer players, the rank correlation coefficient was−0.56 (Table 1). Looking at Table 2, Q1/Q4 was 1.22
and S1/S2 was 1.17, so there may be a slight trend
toward relative age effects. Due to the small numberof subjects, no statistical difference may have been
observed. Previous studies (Figueiredo et al., 2021;
Götze and Hoppe, 2020) had the same problem andthis is a limitation of this research because the numberof national soccer players is very small compared tothe pool of professional soccer players. As mentioned
above, since the relative age effect is observed in themale soccer players who participated in the World
Cup (Pedersen et al., 2022), there may be a slight
trend of the relative age effect in the Japanese malenational team players. A study comparing the relative
age effect of two seasons (the 2000/01 season and the
2010/11 season) about 10 years apart of professionalsoccer players in Europe found that the relative
age effect tended to increase slightly (Helsen et al.,2012). As mentioned above, no relative age effect18

was observed by for male players who participatedin the World Cup until 2014, but a relative age effectwas observed in 2014 and 2018 (Pedersen et al.,2022). Similarly, although no relative age effect wasobserved among female players in the World Cupfrom 2007 to 2019, a relative age effect was observed
for the U-20s in 2018 for the first time since 2002
(Pedersen et al., 2022). These findings indicate anotable shift in the relative age effect trend in recent
years. Hence, since the relative age effect of Japanesenational team players may change over time, it will
be important to accumulate data in the future. In
addition, by position, although there is no significant
difference, MF is 2.00 for Q1/Q4 and 1.39 for S1/
S2, which are higher than other positions. A study
that examined the positional difference in the relative
age effect also reported a tendency more likely to be
seen in goalkeepers and defenders who are required
to be tall and physically strong (Sedano et al., 2015).
The results of this study seem to be different from thetrend of the previous study (Sedano et al., 2015). Dueto the small number of subjects, a clear interpretation
is difficult, but this result may be unique to theJapanese national team. A detailed analysis of eachposition will be necessary in the future.
Among top-level Japanese female soccer players,
the 2010 data did not show a relative age effectFootball Science Vol. 21, 13-20, 2024
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RAE in Japanese National Soccer Players(Nakata and Sakamoto, 2012), but a recent study(from the 2016 season to the 2020 season) did find arelative age effect (Matsuda and Ishigaki, 2023). In
this study, since no relative age effect was observedin female Japanese national soccer players, it wasclarified that the appearance of the relative age effectis different between professional soccer players andnational soccer players in female as well as in male
Japanese soccer players. Because the correlation
coefficient is −0.01, Q1/Q4 is 0.87, and S1/S2 is 0.96
in female Japanese national soccer players, the effectof relative age is thought to be negligible, unlike male
Japanese national soccer players. Because Japanesewomen's soccer won the FIFA Women's World Cup in
2011, the 2012 Olympic Games, and the 2015 FIFA
World Cup runner-up title, the competitiveness ofJapanese female soccer has increased and developed
remarkably. As mentioned above, the relative age
effect of female professional soccer players in Japan
has recently been observed, which is different fromthe past. The relative age effect of female nationalsoccer players may also change in the future due tointensifying competition from younger generations. It
will be necessary to consider this further in the future.

5. Conclusion
As a result of analyzing the relative age effect ofJapanese national soccer players who were called up
to the national team from 2014 to 2020, no relative
age effect was observed for either male or female
Japanese national soccer players. No gender orpositional differences were observed in the ratio of
Q1 to Q4. Since the number of subjects in this study
is not sufficient, it will be necessary to continue theanalysis of the relative age effect of Japanese nationalsoccer players in the future.
Declaration of conflicting interests

There is no conflict of interest.

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Name:
Shigeki Matsuda
Affiliation:
Faculty of Education, Shiga University

Address:
2-5-1 Hiratsu, Otsu, Shiga, 520-0862 Japan
Brief Biography:
2006-2010 Graduate School of Natural Science & Technology,
Kanazawa University
2007-2013 Lecturer, Gifu Shotoku Gakuen University
2013-2014 Associated Professor, Gif u Shotok u Ga k uen
University
2014-2019 Associated Professor, Shiga University
2019- Professor, Shiga University
Main Publications:• M atsuda, S., Nagasawa, Y., Ishihara, T., Demura, T., andKomura, K. (2015). Is it possible to improve collegiate soccer
players’ jump ability? ―A comparison of soccer and volleyball
players’ jump height, arm swing, and body crouch in verticaland header jumps, Football Science, 12: 1-10.
• Matsuda, S., and Ishigaki, H. (2023). Trends in relative age
effects of top-level female soccer players: A Japanese study,
Percept. Mot. Skills, 130(3): 984-998.
• M atsuda, S., and Ishigaki, H. (2023). The recent trend of
relative age effect in Japanese male professional soccer players,
Football Science, 20: 53-61.
• M atsuda, S., Yasui, S., and Naito, Y. (2024). Effects ofplyometric training on heading jump performance and motion
in collegiate soccer players, Cogent Soc. Sci., 10 (1).
Membership in Learned Societies:• Japan Society of Physical Education, Health and Sport Sciences• J apanese Society of Test and Measurement in Health andPhysical Education• Japanese Society of Science and Football• Japan Society of Human Growth and Development

20

Football Science Vol. 21, 13-20, 2024
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