The relative age effect in european professional soccer

Journal of Sports Sciences

ISSN: 0264-0414 (Print) 1466-447X (Online) Journal homepage: http://www.tandfonline.com/loi/rjsp20

The relative age effect in European professional soccer: Did ten years of research make any difference?

Werner F. Helsen , Joseph Baker , Stijn Michiels , Joerg Schorer , Jan Van winckel & A. Mark Williams To cite this article: Werner F. Helsen , Joseph Baker , Stijn Michiels , Joerg Schorer , Jan Van winckel & A. Mark Williams (2012) The relative age effect in European professional soccer: Did ten years of research make any difference?, Journal of Sports Sciences, 30:15, 1665-1671, DOI: 10.1080/02640414.2012.721929 To link to this article: http://dx.doi.org/10.1080/02640414.2012.721929

Published online: 24 Sep 2012.

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Date: 28 July 2016, At: 21:21

Journal of Sports Sciences, November 2012; 30(15): 1665–1671

The relative age effect in European professional soccer: Did ten years of research make any difference?

WERNER F. HELSEN1, JOSEPH BAKER2, STIJN MICHIELS1, JOERG SCHORER3, JAN VAN WINCKEL1 & A. MARK WILLIAMS4 1

Department of Biomedical Kinesiology, Katholieke Universiteit Leuven, Belgium, 2Kinesiology and Health Science, York University, Toronto, Ontario, Canada, 3Institute for Sport Science, Westfa¨lische Wilhelms-University Mu¨nster, Mu¨nster, Germany, and 4Centre for Sports Medicine and Human Performance, School of Sport and Education, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

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(Accepted 14 August 2012)

Abstract The relative age effect (RAE) refers to an asymmetry in the birth-date distribution favouring players born early in the selection year and discriminating against participants born later in the year. While the RAE effect was initially reported in sport more than two decades ago, there have been few attempts to examine whether player selection strategies have changed over time in light of our improved understanding of the phenomenon. We compared the birth-date distributions of professional soccer players in ten European countries over a 10-year period involving the 2000–2001 and 2010–2011 competitive seasons, respectively. Chi-square goodness-of-fit tests were used to compare differences between the observed and expected birth-date distributions across selection years. Generally, results indicated no change in the RAE over the past 10 years in professional soccer, emphasizing the robust nature of this phenomenon. We propose a change in the structure of youth involvement in soccer to reduce the impact of the RAE on talent identification and selection.

Keywords: performance, talent identification, player selection, seasonal variation

Introduction Participation in sports is the primary means by which children maintain health and fitness as well as maximise growth and development. In many sports, participation is organised based on chronological age (typically in one-year age categories) with the goal of providing every child an equal chance to succeed (Musch & Grondin, 2001). However, there can be significant growth and maturational differences amongst members of the same one-year cohort.

For example, if a sport uses 1 January as its ‘cut-off’ date for grouping youth, a child born in January may have as long as a one year advantage or disadvantage (e.g. for female gymnasts) compared with a child born in December of the same calendar year. The difference in age between children born in the same year is referred to as ‘relative age’ (RA) (Barnsley & Thompson, 1988; Barnsley, Thompson, & Legault, 1992) and their performance and participation consequences (regardless of whether they are

relatively younger or older) are known as ‘relative age effects’ (RAE) (Barnsley et al., 1992). For example, researchers have revealed skewed birthdate distributions in elite levels of performance favouring individuals born early in the selection year (Musch & Grondin, 2001; Vaeyens, Philippaerts, & Malina, 2005), presumably because their growth and development is superior to children born late in the selection year (Helsen, Van Winckel, & Williams, 2005; Rummenich & Rogol, 1995).

With respect to talent identification and selection in sport, differences in physical (Tanner & Whitehouse, 1976) and cognitive development (Bisanz, Morrison, & Dunn, 1995) may affect the likelihood of being identified as ‘talented’. Subsequently, children selected for talent development programmes appear to have better capacities and more intrinsic (observed competence) and extrinsic motivation (appreciation of coaches and parents). This increased motivation, together with the perceived competence, stimulates these children to practice

Correspondence: Werner F. Helsen, Department of Biomedical Kinesiology, Katholieke Universiteit Leuven, Tervuursevest 101, Heverlee (Leuven), 3001 Belgium. Email: werner.helsen@faber.kuleuven.be ISSN 0264-0414 print/ISSN 1466-447X online Ó 2012 Taylor & Francis http://dx.doi.org/10.1080/02640414.2012.721929

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more and further improve their skills (Helsen et al., 2005; Shearer, 1967). This latter process leads to a vicious circle where early-born children have an increasing and persistent advantage over late-born children both in school (Sharp, 1995) and in sport (Helsen et al., 2005).

Musch and Grondin (2001) proposed that RAEs only manifest themselves when a significant degree of competition is present. In addition, and similar to soccer, sports such as ice hockey (Grondin & Trudeau, 1991), American football (Glamser & Marciani, 1990), baseball (Thompson, Barnsley, & Stebelsky, 1991), basketball (Delorme, Chalabaev, & Raspaud, 2010; Schorer, Neumann, Cobley, Tietjens, & Baker, 2011), cricket (Edwards, 1994), and tennis (BaxterJones, 1995; Dudink, 1994) are breeding grounds for RAEs because weight, height and strength are important in these sports. Sports such as gymnastics or dance are less likely to show RAEs because movement competency is more important and having a large body size or mass may present a disadvantage to the athlete (Delorme, Boiche, & Raspaud, 2010).

In both professional and youth soccer, the RAE has been a research topic since the early 1990s.

Dudink (1994) noted very strong RAEs in professional soccer in the Netherlands and England (see also Verhulst, 1992). Similarly, Helsen et al. (2005) noted RAEs in international youth teams (i.e. under 15 to under 18 years of age) reflecting a disproportionate number of relatively older players. Likewise, Jime´nez and Pain (2008) found a RAE in first and second divisions in Spain as well as in youth soccer. A strong RAE was also found in non-European countries (Japan, Brazil and Australia) suggesting that the phenomenon is present in a variety of climatic and socio-cultural environments and is independent of different cut-off dates (Musch & Hay, 1999).

Researchers have also considered this effect over time. Cobley, Schorer and Baker (2008) found a skewed distribution across the history of the Bundesliga in Germany, both for players and coaches.

Historically, there were no decreases in the last decades for ice-hockey (Wattie et al., 2007) or soccer in Germany (Cobley et al., 2008). However, considering the increased effort put into research on this topic over the last two decades, this trend might have been reversed in some countries. As Helsen and others have proposed (Barnsley et al., 1992; Boucher & Halliwell, 1991; Helsen, Starkes, & Van Winckel, 2000; Helsen et al., 2005; Musch & Grondin, 2001), raising awareness of the negative impact of this phenomenon through coach education should be part of the solution. In Germany, for example, an article advocating action was recently published in a journal read by many coaches (Lames, Augste, Dreckmann, Go¨rsdorf, & Schimanski, 2008). In the same way, the soccer federation in

Belgium created U16-F and U17-F ‘future’ teams in addition to the regular U16 and U17 teams. These future teams mainly consist of ‘late maturers’.

With respect to the impact of time on the manifestation of the RAE, there are two viable hypotheses. The first one holds that the RAE would have decreased over the last decade based on the considerable increase in research in this area accompanied with the various solutions proposed to reduce its impact. The second hypothesis predicts that the RAE did not decrease at all over the course of the past ten years, and may even have increased slightly over this time. The main reason is that in the 2000–2001 competitive season players were exposed to a different cut-off date in school than in the sport club. Before 1997, the sport selection year started in August, while the education year started in January, whereas since 1997 the selection periods for both education and sport in every country start in January.

An exception is England, where both selection periods start in September. As a result, players in the 2010– 2011 competitive season were exposed to the same cut-off date for education and sport during their player development, which may have increased the effect.

Our main aim in this paper was to examine the birthdate distributions in prominent soccer competitions across Europe over two seasons a decade apart (i.e.

2000–2001 and 2010–2011) to examine whether the magnitude of the effect has changed over time.

Methods Participants The birth-date distributions from all professional players in the 2000–2001 and 2010–2011 competitive seasons were examined. Table I provides an Table I. Overview of the number and percentage home country players and foreigners in the 2000-2001 and 2010-2011 competitive seasons.

Country

Players

Total (N)

England Portugal Germany Belgium Netherlands Spain France Italy Denmark Sweden Total

% Home country

% Foreigners

2000

2010

2000

2010

2000

596 432 511 442 450 486 473 496 319 470 4675

565 428 535 407 446 490 535 558 285 412 4661

53.7 56.0 57.3 61.1 65.1 65.6 71.9 64.9 86.5 94.0 66.5

40.7 44.2 52.7 49.4 59.2 64.3 60.0 57.3 73.3 74.0 56.6

47.3 44.0 42.7 38.9 34.9 34.4 28.1 35.1 13.5 6.0 33.5

2010 59.3 55.8 47.3 50.6 40.8 35.7 40.0 42.7 26.7 26.0 43.4

Relative age in professional soccer overview of the number of players in the specific countries examined. Engebretsen et al. (2010) noted that births in some countries are not registered until school starts, leading to uncertainty about the validity of these data. Therefore, only home country players were used to test for significant differences.

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Procedure First, birth-date data from players competing in both the 2000–2001 and 2010–2011 competitive seasons were collected from the official sites of the clubs.

These data were checked with resources from the governing bodies. Subsequently, the number of players born per month and per quarter-year was acquired. In line with previous work (Helsen, Starkes, & Van Winckel, 1998; Helsen et al., 2005), August was coded as ‘month 1’ and July as ‘month 12’ for the 2000–2001 season because, until 1997, the start of the selection year was 1 August, except for England. Following the guidelines of the Fe´de´ration Internationale de Football Association (FIFA), the national associations have used 1 January as the start of the selection year since 1997.

As such, the change in cut-off date was considered to have no impact as the players from the 2000–2001 season were all subjected to the same cut-off date throughout their participation in the various youth categories. For the 2010–2011 season, however, January was coded as ‘month 1’ and December as ‘month 12’, except for England where the start of the selection year was still 1 September.

Data analysis For the comparison of quartiles, Chi-square goodness-of-fit tests were used to compare differences between the observed and expected birth-date distributions across the quarters of the selection year. This procedure was first undertaken for both distributions of 2000–2001 and 2010–2011 separately. Additionally, we compared the distribution of the 2000–2001 season with the distribution of the 2010–2011 season using Chi-square tests. We report the effect size (w) and, if applicable, the test power (1–b; Fald, Erdfelder, Lang, Buchner, 2007). For each of these tests, the level of significance was set at P 5 0.05.

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2010–2011 competitive season, while the percentage of foreigners increased from 33.5% to 43.4%, respectively (see Table I).

When we considered each country separately, only four countries showed less than the approximate 10% increase in foreign players: Germany; the Netherlands; Spain; and Italy. The highest increase was noted for Sweden with 20% of foreign-born players compared with 6% in 2000–2001.

Relative age effects Figure 1 presents the total quartile distribution from 2000–2001 to 2010–2011, and reflects the skewed distribution with the greater number of players coming from the beginning of the selection year and a decrease in the number of players born later in the selection year. As expected, there were significant relative age effects for the season 2000–2001, w(3, n ¼ 3111) ¼ 61.07, P 5 0.01, w ¼ 0.14, as well as for the season 2010–2011, w(3, n ¼ 2636) ¼ 85.34, P 5 0.01, w ¼ 0.18. When the relative percentage of home country players is considered, this effect appears stronger in the 2010–2011 season compared with the 2000–2001 season. Comparative analysis of both distributions revealed a significant increase in this effect from season 2000–2001 to 2010–2011, w(3, n ¼ 5747) ¼ 19.67, P 5 0.05, w ¼ 0.06.

Table II shows the birth-quartile distributions of the home country professional players in the 2000– 2001 and 2010–2011 competitive seasons from the same ten European countries.

For the 2000–2001 competitive season, most of the birth-date distributions are asymmetric, as revealed by the results of the statistical analysis, except for Portugal and Spain. In a few countries, the RAE results approached conventional levels of significance (the Netherlands and Sweden). The most significant effect was found in France. Out of a

Results Composition of professional leagues While the number of players in the ten leagues investigated did not differ, on average, the percentage of home country players decreased from 66.5% in the 2000–2001 competitive season to 56.6% in the

Figure 1. Comparison between the relative birth-date distribution of professional players in the 2000–2001 and 2010–2011 competitive seasons.

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0.21 0.28 0.11 0.28 0.26 0.17 0.25 0.27 0.20 0.21 0.28 0.20 50.05 n.s.

50.05 50.05 50.05 50.05 50.05 50.05 50.05 50.05 50.05

total of 340 players, there were 117 professional players born in the first quarter and only 61 players in the last quarter. Overall, it is clear that there is an overrepresentation of players born in the first quarter of the selection year and an underrepresentation of players born in the last quarter of the selection year.

Comparable results were found for the 2010–2011 competitive season. Asymmetric birth-date distributions were found in all countries, except in Portugal.

The greatest asymmetry was observed in Sweden where, out of a total of 305 players, 118 players were born in the first quarter and only 46 players in the last quarter. Overall, there is an overrepresentation of players born in the first quarter of the selection year and an underrepresentation of players born late in the selection year.

In a last step, we compared the birth-quartile distributions of the 2000–2001 and the 2010–2011 seasons. As can be seen in Table III, significant differences between these distributions with an increasing RAE were revealed for Belgium, Denmark, England, Germany, Spain and Sweden. Only non-significant changes in the distributions were found for France, Italy, Portugal and the Netherlands.

0.13

29.6 24.9 36.5 29.9 27.3 32.7 34.0 29.1 32.1 38.7 31.9 0.20 0.13 0.17 0.19 0.12 0.08 0.26 0.21 0.20 0.05 0.14

0.35 0.19

Discussion

*Start of the selection year: September

England* Portugal Germany Belgium Netherland Spain France Italy Denmark Sweden Total

314 242 293 270 293 319 340 322 276 442 3111

33.1 24.4 31.4 30.7 28.3 25.9 34.5 29.5 25.4 28.7 29.3

22.9 28.1 25.9 20.7 27.0 24.8 25.0 28.0 33.3 27.1 26.5

23.3 28.1 22.5 21.1 24.9 27.3 22.6 26.4 25.0 23.8 24.5

20.7 19.4 20.1 27.4 19.8 22.0 18.1 16.1 16.3 20.4 19.8

13.6 4.0 8.3 10.2 4.0 1.9 22.6 13.9 11.0 1.2 58.9

50.05 n.s.

50.05 50.05 n.s. n.s.

50.05 50.05 50.05 n.s.

50.05

0.36

230 189 282 201 264 315 321 320 209 305 2636

32.2 27.5 19.9 32.8 30.3 27.0 25.2 30.6 27.3 22.9 26.1

21.7 27.5 26.2 17.4 25.0 24.1 25.2 22.5 23.9 23.3 23.6

16.5 20.1 17.4 19.9 17.4 16.2 15.6 17.8 16.7 15.1 18.4

18.6 2.3 23.3 13.4 8.0 20.4 23.5 13.5 9.1 24.6 101.9

w p X2 Q4 Q3 Q2 Q1 N w N

Q1

Q2

Q3

Q4

X2

p

1–b

2010/11 2000/01

Table II. Overview of the birth quartile distribution of home country players in ten European countries in the 2000–2001 and 2010–2011 competitive seasons.

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1–b

W.F. Helsen et al.

In line with previous studies examining the RAE in soccer in Germany (Cobley et al., 2008) and in Spain (Jime´nez & Pain, 2008), the birth-date distributions of professional soccer players in ten European countries were examined. We compared the birth date distributions among professional players in the 2000–2001 and 2010–2011 competitive seasons. In the 2000–2001 competitive season, all countries, with the exceptions of Portugal and Spain, showed a significant relative age effect. In the 2010–2011 season, only Portugal did not show a RAE. There has been no decrease in the prevalence of the RAE during the last decade. The birth-date distribution of the 2010–2011 competitive season shows that 31.9% of the players were born in the first quarter of the selection year and 18.4% were born in the last quarter of the selection year, compared with 29.3% and 19.8% respectively in the 2000–2001 season. These data suggest that despite solutions being proposed in the literature there has been little impact on the effect. Conversely, Spain showed no RAE in the 2000–2001 competitive season, whereas a significant effect was noted in the 2010–2011 competitive season (c.f. Jime´nez & Pain, 2008).

Previously, researchers have suggested that the existence of, and possibly increase in, prevalence of the RAE in soccer is driven by three mechanisms (Helsen et al., 1998). First, children receive more playing time as a result of a developmental advantage

Relative age in professional soccer

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Table III. Difference in birth quartile distribution between 2000–2001 and 2010–2011 seasons.

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England Portugal Germany Belgium Netherlands Spain France Italy Denmark Sweden Total

Q1

Q2

Q3

Q4

X2

p

w

3.5 70.5 75.1 0.8 1.0 76.8 0.5 0.4 76.7 710.0 72.6

79.3 0.6 6.0 712.1 73.3 72.2 70.2 72.6 6.0 4.2 0.4

1.6 0.6 73.7 3.7 70.1 3.2 72.6 3.9 1.1 0.5 0.9

4.2 70.7 2.7 7.5 2.4 5.8 2.5 71.7 70.4 5.3 1.4

27.8 0.3 18.5 46.4 4.1 24.6 4.0 6.4 14.1 41.2 20.4

5.05 n.s.

5.05 5.05 n.s.

5.05 n.s. n.s.

5.05 5.05 5.05

0.23 0.02 0.18 0.31 0.08 0.20 0.08 0.10 0.17 0.23 0.05

rather than their level of proficiency. A related issue is that youth soccer players are organised into twoyear age categories, which may place greater significance on the importance of developmental differences between children. Players born in the first quarter of the selection period are chronologically older than their later born teammates, which may lead to a difference in strength, height, weight and coordination (Barnsley et al., 1992), characteristics that are highly variable before and during puberty. Second, Ward and Williams (2003) proposed that early born children have better technical skills and more tactical insight due to more experience as a result of earlier exposure to practice and competition (see also Helsen et al., 1998; Ward, Hodges, Williams, & Starkes, 2004). Finally, players are exposed much earlier to competition in soccer than in many other domains (Helsen et al., 2005), which promotes the identification and selection of talent at early stages of development. Musch and Grondin (2001) proposed that intense competition is a fundamental element underpinning the RAE in sports.

We hypothesized that the RAE would have decreased over the last decade based of increased awareness fostered by the considerable increase in published research on this topic, accompanied with the various solutions proposed to reduce its impact.

However, the prevalence of the RAE does not seem to have decreased over the course of the past ten years; on the contrary, there is some evidence that it may have increased slightly over this time. Although the precise reason for the lack of change is difficult to discern, one specific change that occurred may have had some influence. In the 2000–2001 competitive season, players were exposed to a different cut-off date in education. Before 1997, the sport selection year started in August while the education year started in January. Since 1997, the selection periods for both education and sport in most countries start in January. As a result, players in the 2010–2011 competitive season were exposed to the same cut-off date for education and sport during their player

1–b

0.06

0.37 0.35 0.55

development. This may have had a greater impact on the RAE than has been considered until now.

Given that our analyses show no reduction in the effect over the past 10 years, more proactive measures are required by researchers and sport administrators. A number of publications (Barnsley et al. 1992; Helsen et al., 1998, 2005; Helsen, Hodges, Van Winckel, & Starkes, 2000; Musch & Grondin, 2001) have proposed a range of options to eliminate the RAE (see Cobley, Wattie, Baker, & McKenna, 2009). In their review, Musch and Grondin (2001) differentiate between classification systems based on biological age, chronological age, multiple squads based on multiple standards, and warning practitioners. In many sports, classification systems based on biological age are difficult to organise, and consequently alternative solutions based on chronological age should be considered.

For instance, every year the cut-off date could be shifted to give each child the opportunity to be the oldest in their age category (Barnsley et al., 1992; Boucher & Halliwell, 1991; Helsen, Starkes, & Van Winckel, 2000, Helsen et al., 2005; Musch & Grondin, 2001). In individual sports, for example, cut-off dates can be determined differently for each competition. In swimming there is no fixed cut-off date. According to Ryan (1989), this can prevent RAEs if the accumulation of key competitions are not all scheduled in specific months each year.

Unfortunately, this age-grouping system in swimming is not applicable in team sports. When the age categories are limited to 9 (Boucher & Halliwell, 1991), 15 or 21 months (Grondin, Deshaies & Nault, 1984), the cut-off date will automatically change with the consequence that every child has the advantage of being the oldest in a cohort.

Rotating the cut-off date is a relatively simple, structural solution that could be easily used by the governing bodies. As it has not yet been presented in soccer, we illustrate below how a change from the current grouping system to a system with a 21-month

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Table IV. Overview of a grouping system with 21 months for soccer, season X. The numbers between brackets indicate the age of the players.

Thanks to the rotating cut-off date, each birth quarter is now being advantaged. The different colours indicate different birth cohorts. The names of the age categories are named the same as in table 7.

Categories:Quarters: 1. Most advantaged players 2.

3.

4.

5.

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6.

7. Most disadvantaged players

U10 April (10) May (10) June (10) July (10) August (10) September (10) October (10) November (10) December (10) January (9) February (9) March (9) April (9) May (9) June (9) July (9) August (9) September (9) October (9) November (9) December (9)

U12 July (12) August (12) September (12) October (12) November (12) December (12) January (11) February (11) March (11) April (11) May (11) June (11) July (11) August (11) September (11) October (11) November (11) December (11) January (10) February (10) March (10)

rotating cut-off date might affect players within the U10, U12, U14 and U16 age categories (Table IV).

Table IV shows the impact of a rotating cut-off date compared with the current system where children born in the same year are grouped together throughout development. In the proposed grouping system, children born in the same calendar year are not necessarily grouped together. This new system results in several important changes. First, the cut-off date changes in each category and has the consequence of each child being the oldest one in his age category for a specific time period. Second, each category only has seven quarters with the consequence of fewer children in each age category. Third, the oldest U16 is 15 years old, whereas in the old system the oldest U16 was 16 years old. This change means that children will move on to the next category one year earlier than in the old system.

Finally, moving on to the next category does not happen with the same birth cohort. As a consequence of this change, two players who play together in one season, do not play together in the next season; however, they may still be in the same class in school.

Since 1997, the cut-off date at school has been the same as in the sports clubs in many countries.

Specifically, this means that the same children are among the oldest both in school and club and, therefore, systematically advantaged while the ones born at the end of the year are systematically disadvantaged whenever they go to school or participate in a sports club. While this was certainly not intentional when FIFA moved the cut-off date from August to January, the impact is clear. In future

U14 October (14) November (14) December (14) January (13) February (13) March (13) April (13) May (13) June (13) July (13) August (13) September (13) October (13) November (13) December (13) January (12) February (12) March (12) April (12) May (12) June (12)

U16 January (15) February (15) March (15) April (15) May (15) June (15) July (15) August (15) September (15) October (15) November (15) December (15) January (14) February (14) March (14) April (14) May (14) June (14) July (14) August (14) September (14)

studies, researchers should examine to what extent the use of rotating cut-off dates may structurally solve the persistent inequalities that are associated with the RAE in talent detection and selection in high-performance sport.

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