Relative Age Effects in Korean Football: Analysis of Age-Specific International Teams

Tae-Seok Jeong; Sang-Yeol Bang; Sehwan Park; Young-Soo Lee; Yong-Rae Kim; Young-Seok Kim

doi:10.5763/kjsm.2019.37.3.94

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Jeong, Bang, Park, Lee, Kim, and Kim: Relative Age Effects in Korean Football: Analysis of Age-Specific International Teams

Clinical Article

Korean J Sports Med 2019;37(3):94-100.

Published online: 20 January 2019

DOI: https://doi.org/10.5763/kjsm.2019.37.3.94

Relative Age Effects in Korean Football: Analysis of Age-Specific International Teams

Tae-Seok Jeong¹, Sang-Yeol Bang¹, Sehwan Park¹, Young-Soo Lee², Yong-Rae Kim², Young-Seok Kim^3,

¹SPIK Sports Medicine Clinic and Performance Center, Seoul, Korea

²Department of Sports Science, Sejong University, Seoul, Korea

³Korea Sport Industry Development Institute, Pohang University of Science and Technology, Pohang, Korea

Correspondence: Young-Seok Kim Korea Sport Industry Development Institute, Pohang University of Science and Technology, 77 Cheongam-ro, Nam-gu, Pohang 37673, Korea Tel: +82-54-279-8843, Fax: +82-54-279-8852, E-mail: tessj@hanmail.net

^∗ This research project was supported by the Sports Promotion Fund of Seoul Olympic Sports Promotion Foundation from Ministry of Culture, Sports and Tourism.

Received 5 July 2019 Revised 12 August 2019 Accepted 13 August 2019

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose

This study aimed to identify relative age effects of South Korea national male football teams that participated in 38 international competitions in age-specific categories from 2000 to 2018; U-16 (n=176), U-17 (n=82), U-19 (n=198), U-20 (n=147), and U-23 (n=166).

Methods

Available information on birth-dates, heights, and body weights of South Korean elite male football players was collected from the official websites. Chi-square test was conducted and odds ratios were calculated with 95% confidence interval in order to examine differences of quarter distribution between expected and observed subgroups.

Results

The birth distributions observed in each team were significantly different than those expected in general population of the same age (U-16: χ²=59.364, p＜0.05; U-17: χ²=36.829, p＜0.05; U-19: χ²=51.697, p＜0.05; U-20: χ²=39.531, p＜ 0.05) except U-23 (χ²=17.759, p=0.087). The magnitude of birth distribution was 3.2 times higher in the first quarter compared to that in the fourth quarter and was decreased in accordance with age. In accordance with age, the distribution of “competition age group” was significantly decreased in each team (U-16, 91%; U-17, 89%; U-19, 76%; U-20, 63%; U-23, 42%; p＜0.05) but that of “under-competition age group” was increased (U-16, 9%; U-17, 11%; U-19, 24%; U-20, 37%; U-23, 58%; p＜ 0.05). There is also significant difference in distribution between both “competition” and “under-competition age group” at the same tournament category (p＜0.05).

Conclusion

Conclusively, these findings indicate that Korean players who are in the early stage of development have higher “relative age effects” than those in the late stage of development. This may implicate that it is necessary to develop strategies for relatively late-mature players who have potentials in terms of skills and intelligence of football.

Keywords: Football, Relative age, Talent

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Fig. 1.

Quarterly distribution of birth-date by each age-specific subgroup. Q1: January to March, Q2: April to June, Q3: July to September, Q4: October to December.

Fig. 2.

Birth-month distribution of players by age-specific subgroups. Distribution of each subgroup was significantly different in accordance with month (p＜0.05).

Fig. 3.

Distribution of “competition age group” and “under-competition age group” significantly decreased (∗) and increased (^†) in accordance with age, respectively. In each age-specific subgroup, there were significant differences in the distribution between both groups (^‡).

Table 1.

Age-specific international competitions included in the study

Group	U-16 (n=176)	U-17 (n=82)	U-19 (n=198)	U-20 (n=147)	U-23 (n=166)∗
Tournament	8 AFC Championship (2002, 2004, 2006, 2008, 2012, 2014, 2016, 2018)	4 FIFA WC (2003, 2007, 2009, 2015)	9 AFC Championship 2002, 2004, 2006, 2008, 2010, 2012, 2014, 2016, 2018)	7 FIFA WC (2003, 2005, 2007, 2009, 2011, 2013, 2017)	5 AG (2002, 2006, 2010, 2014, 2018), 5 OG (2000, 2004, 2008, 2012, 2016)

AFC: Asian Football Confederation, FIFA: Federation Internationale de Football Association, WC: World Cup, AG: Asian Games, OG: Olympic Games.

^∗ In U-23 subgroup, players who were over-competition age (i.e., wild card) were excluded.

All data were sourced from www.kfa.or.kr, www.fifa.com, and www.the-afc.com.

Table 2.

Comparison of differences between the observed and expected birth-date distributions across the four quarters

Group	Number	Median birth month	χ²	p-value	Regression coefficient
Group	Number	Median birth month	χ²	p-value	β	p-value
U-16	176	April	59.364	0.000	−0.879	0.000
U-17	82	April	36.829	0.000	−0.762	0.000
U-19	198	April	51.697	0.000	−0.752	0.000
U-20	147	April	39.531	0.000	−0.751	0.000
U-23	166	June	17.759	0.087	−0.591	0.000
Entire cohort	769	April	156.841	0.000	−0.903	0.000

^χ2 : chi-square test.

Table 3.

The magnitude of quarterly distribution of players in each age-specific subgroup

Group	Number	Q1/Q4	Q2/Q4	Q3/Q4
U-16	176	4.0 (1.7−9.5)	2.5 (1.0−6.2)	1.5 (0.6−4.0)
U-17	82	3.8 (1.6−8.7)	2.8 (1.2−6.5)	0.8 (0.3−2.3)
U-19	198	3.5 (1.5−8.2)	2.2 (0.9−5.2)	1.7 (0.7−4.1)
U-20	147	3.7 (1.6−8.5)	2.1 (0.9−5.0)	1.7 (0.7−4.1)
U-23	166	2.1 (0.9−4.7)	1.5 (0.6−3.5)	1.7 (0.7−3.9)
Entire cohort	769	3.2 (1.4−7.3)	2.1 (0.9−4.9)	1.5 (0.6−3.8)

Values are presented as odds ratio (95% confidence interval).

Q1: January to March, Q2: April to June, Q3: July to September, Q4: October to December.

Table 4.

Mean height and body weight of players in accordance with birth-quarter

Group	Total	Q1	Q2	Q3	Q4
U-16
Height (m)	1.78±0.06	1.78±0.05	1.78±0.06	1.78±0.05	1.78±0.06
Body weight (kg)	68.4±6.1	68.6±5.5	68.5±7.2	67.4±5.5	68.8±6.3
U-17
Height (m)	1.79±0.06	1.78±0.06	1.79±0.06	1.80±0.05	1.81±0.06
Body weight (kg)	68.4±6.1	68.3±7.3	69.8±7.0	70.1±5.1	69.7±7.4
U-19
Height (m)	1.80±0.06∗	1.80±0.06	1.81±0.06	1.80±0.06	1.80±0.07
Body weight (kg)	71.8±6.6∗^,†	71.6±6.8	72.7±6.3	71.6±5.9	71.0±8.1
U-20
Height (m)	1.81±0.07∗	1.81±0.07	1.82±0.07	1.81±0.06	1.81±0.08
Body weight (kg)	72.7±6.9∗^,†	72.2±6.6	74.3±7.3	71.8±5.6	72.6±9.2
U-23
Height (m)	1.81±0.06∗	1.80±0.05	1.82±0.07	1.80±0.05	1.83±0.06
Body weight (kg)	73.7±6.3∗^,†	72.9±5.4	75.1±7.5	72.4±5.9	75.4±6.2

Values are presented as mean±standard deviation.

Q1: January to March, Q2: April to June, Q3: July to September, Q4: October to December.

^∗,† Significantly different from U-16 and U-17 subgroup, respectively (p＜0.05).

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