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The role of a relative age effect in the first winter Youth Olympic Games in 2012
  1. Christian Raschner,
  2. Lisa Müller,
  3. Carolin Hildebrandt
  1. Department of Sport Science, University of Innsbruck, Innsbruck, Austria
  1. Correspondence to Dr Christian Raschner, Department of Sport Science, University of Innsbruck, Fuerstenweg 185, A-6020 Innsbruck; Christian.Raschner{at}uibk.ac.at

Abstract

Background Owing to the separation into age groups at the first winter Youth Olympic Games (YOG), athletes differed in age by up to two years, leading to a potential relative age effect (RAE).

Objective The purpose of this study was to define the role of the RAE in the first winter YOG with regard to sex, type of sport and performance.

Methods The birth dates and anthropometric data of all 1021 athletes (557 male, 464 female, 14–19 years old) participating in 15 sports were analysed. A χ2 test was used to assess the difference between the observed and expected birth distributions. ANOVA (analysis of variance) and Kruskal−Wallis analyses were used to investigate differences in anthropometrics.

Results The birth date distribution of the overall sample was significantly different from an equal distribution, with an over-representation of athletes born shortly after the cut-off date (χ2=284.7, p<0.001). A significant RAE was found in both male (χ2=245.1, p<0.001) and female competitors (χ2=74.6, p<0.001). An analysis based on the type of sport showed an RAE in all categories (strength—χ2=229.9, p<0.001, endurance—χ2=60.4, p<0.001 and technique-related sports χ2=25.2, p=0.001). Relatively older competitors were also over-represented among medal winners (χ2=47.9, p<0.001). Relatively older male competitors were significantly taller (p=0.005) and heavier (p<0.001) than younger competitors. No differences were found in female competitors.

Conclusions The results suggest that relative age had a highly significant influence on participation in various sports regardless of sex. A possible strategy to reduce the RAE would be a fixed quota for each birth year within the two-year age group across events.

  • Adolescents
  • Elite performance

https://doi.org/10.1136/bjsports-2012-091535

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    Introduction

    In January 2012, the International Olympic Committee (IOC) held the first winter Youth Olympic Games (YOG) in Innsbruck, Austria, for 14-year-old to 19-year-old athletes. Overall, 1021 young athletes from 70 different countries participated in 15 sports and 63 disciplines. To guarantee fair competition and reflect age-related development, children in sports are classified according to their chronological ages, with 1 January often used as the cut-off date for each selection year.1–3 Because of this separation into age groups, athletes can differ in age by up to 1 year, leading to a relative age effect (RAE). A RAE exists when the birth month distribution of a selected sports group differs from the even distribution of the normal population such that there is an over-representation of athletes born in the first quarter after the cut-off date.4 As a consequence, these age differences of almost 1 year can invariably lead to cognitive, physical, emotional and motivational differences between athletes born shortly after the cut-off date and those born at the end of the year.5 ,6 The age of onset of pubertal development can vary greatly for boys and girls particularly in early to mid-adolescence.7 Influences on the timing of pubertal development include genetics and a broad range of environmental factors.8 Cognitive development also varies between individuals of this age group and the brain is not fully mature until early adulthood.9 As a consequence, normal variations in the timing and progression of puberty can influence youth sport performance,3 so more research in this field is recommended.

    Furthermore, the age difference between two individuals within the same age group can result in different experiences in training and competition.1 ,5 Apart from these differences, the relatively older athletes tend to be physically more developed, and anthropometric variances are particularly significant.1 ,6 ,10 ,11 Owing to these two advantages, an enhanced performance on the part of the relatively older athletes can follow, and these children are likely to be identified as talented if they perform better than others. This initial small performance advantage can lead to a large advantage that often cannot be compensated for by the relatively younger athletes; therefore, younger athletes often drop out of sports. In this context, Helsen et al1 have identified a ‘vicious circle’.

    Research regarding the RAE has clearly focused on team sports, such as soccer,1 ,6 ,11–15 ice hockey,10 ,16–19 baseball,17 handball,20 ,21 basketball,22 volleyball,23 ,24 rugby25 and football.26 Individual sports have been much less frequently analysed. However, data are available from analyses of tennis,27 ,28 swimming,29 track and field,29 shooting30 and alpine skiing.31 In general, the RAE phenomenon has been confirmed with only a few exceptions.

    The RAE is especially significant in strength-related and power-related sports or in sports with high demands on body size and power and that entail direct competition with a single opponent.4 In contrast, the most compositional sports, such as rhythmic gymnastics or gymnastics, are either not affected by an RAE or show a reversed RAE, with an over-representation of relatively younger athletes.4 ,22 ,32

    Apart from these findings, a higher RAE is more likely to be found in culturally popular and important sports. If the number of people competing for just one place in a squad is high and if, as a consequence, the selection pressure is also high because the available infrastructure is grossly exceeded, then relatively older athletes are more likely to be identified as talented, and therefore they will be selected.2 ,5 ,18 ,32 For example, in Canada, a high RAE was found in the most competitive sport, ice hockey,18 whereas in volleyball, a less popular sport in that country, a significant RAE was not found.5 Most of the studies concerning the RAE have investigated male athletes, and the findings for female athletes have been less frequent and inconsistent. Often, the relative age differences are much less pronounced among girls, and as a consequence, an RAE often does not occur in female contexts. The above-mentioned aspects have often been investigated for single disciplines. However, data on major single junior events are lacking. At the YOG 2012, only one or two athletes per country were allowed to start in each discipline, leading to a high selection pressure within the national nomination process. In most sports, competitors from 2 birth years were allowed to participate. As a consequence, we assumed that a high RAE could exist due to the selection pressure in the national talent promotion systems. The aim of the present study was to define the role of relative age in the first YOG 2012 with regard to sex and performance. Furthermore, we analysed different types of sports by comparing the occurrence of an RAE in strength-related and power-related, endurance-related and technique-related sports. We hypothesised that the RAE would have a clear impact on the selection procedures, favouring relatively older athletes.

    Methods

    Procedures

    To assess the prevalence of an RAE in the first YOG, a list with the birthdates, disciplines and anthropometric data of all of the participants was provided by the IOC. In general, 1 January was used as the cut-off date for the selection year in the single sports of the YOG. The age groups’ eligibility for participation in a sport was defined by the relevant international federations. The birth months and years of the athletes’ eligibility were used to establish eight groups of birth quartiles, starting with 1 January (table 1). To establish the RAE in various types of sports, the different sports were divided into three groups based on the current literature (table 2). The categories of strength-related and endurance-related sports were determined based on whether power or endurance was performance predictive. The determination of technique-related sports was based on judging points. Data from 1021 young athletes (557 male and 464 female) from 70 different countries were analysed. Table 3 presents the anthropometric data (means and SDs) for male and female athletes divided by type of sport and according to the two eligible age groups.

    View this table:
    Table 1

    Age group division

    View this table:
    Table 2

    Type of sport

    View this table:
    Table 3

    Anthropometric data of participants according to sport and age group

    The study was approved by the institutional review board and by the IOC.

    Statistics

    A χ2 test was used to assess the difference between the observed and the expected birth distribution for all participants. According to previous research, we assumed an equal distribution among the quartiles.10 ,16 ,21 Additionally, data on the birth quarter distribution of the general populations of Austria, Germany and Switzerland for the same birth years as the participants of the YOG (1993–1997) have shown an equal distribution of birthdates (see online supplementary figure S6). The χ2 tests were also used to assess gender and type of sport-specific differences of the RAE regarding the distance of the birth-month to the month containing the cut-off date (January). A one-way analysis of variance (ANOVA) was used to test for differences in the weights of male athletes. Based on non-parametric data, the Kruskal-Wallis one-way ANOVA was used to compare the other anthropometric parameters among the athletes. ORs were calculated for birth quartile distribution according to sex, type of sport and medal winners. The level of significance was set at p<0.05. All of the calculations were performed using PASW Statistics V.18.0.

    Results

    In total, 1021 athletes competed in 15 sports. Ice hockey and alpine skiing had the highest participation rates. The majority of both male (n=434, 78%) and female (n=317, 68%) athletes were born in the first year of eligibility (without considering ice hockey). The distribution of participants according to their sex and eligible age group are presented in table 4. The χ2 statistics for the overall sample showed a significant difference from an equal distribution (χ2=284.7, p<0.001), with an over-representation of athletes born in Q1(1) and an under-representation of athletes born in Q4(2). The data also show a significant RAE in both the male athletes (χ2=245.1, p<0.001) and female athletes (χ2=74.6, p<0.001; figure 1), with a significant stronger RAE in male athletes (χ2=24.8, p=0.01).

    View this table:
    Table 4

    Eligibility of participants according to sport and sex

    Figure 1
    Figure 1

    Quartile distribution of all YOG participants according to sex.

    For the overall sample and according to gender the descriptive OR and the corresponding χ2 for each quarter can be found in table 5. When comparing the individual quartiles, it becomes evident that the size effect increased with the quartile for the total sample and in both the male and female athletes.

    View this table:
    Table 5

    Descriptive OR across all birth quarters according to sex

    An analysis of the birth quartile distribution based on the type of sport (figure 2) showed an RAE in all categories, but the RAE was most pronounced in strength-related sports (χ2=229.9, p<0.001), followed by endurance-related sports (χ2=60.4, p<0.001) and finally technique-related sports (χ2=25.2, p=0.001). No significant differences between types of sports concerning the distance of the birth-month to the month January were demonstrated. A closer examination of the different competitive events revealed the highest RAE in alpine skiing (χ2=60.4, p<0.001). In endurance-related sports, the highest differences in quartile distribution were found for cross-country skiing (χ2=22.3, p=0.002), followed by speed skating (χ2=28.4, p<0.001). Within the technique-related events, the highest RAE was found in snowboarding (χ2=23.6, p<0.001).

    Figure 2
    Figure 2

    Quartile distribution of all YOG participants according to the type of sport.

    Table 6 presents the descriptive OR and corresponding χ2 for each birth quarter according to the type of sport. In strength-related sports, the relatively older athletes were approximately 11.5 times more likely to participate in the YOG. For endurance-related and technique-related sports, the risk of an RAE was less likely across the birth quarters.

    View this table:
    Table 6

    Descriptive OR across all birth quarters according to the type of sport

    Table 7 reflects the quartile distribution between the two eligible age groups. Months of birth were categorised as Q1=January–March, Q2=April–June, Q3=July–September and Q4=October–December. Independent of the eligible year, a strong RAE was found for the total sample and strength-related sport. In endurance-related sport only athletes from the relatively older age group showed an RAE.

    View this table:
    Table 7

    Quartile distributions according to eligible year

    A total of 136 medals (excluding team events) were awarded among the 1021 athletes. As shown in figure 3, relatively older medal winners were over-represented compared to athletes born at the end of the second eligible year. Statistical analyses revealed a significant total RAE (χ2=47.9, p<0.001). Furthermore, differentiating between sexes revealed differences between male (χ2=32.9, p<0.001) and female (χ2=17.3, p=0.016) medal winners. A detailed look at the relative age distribution across the quarters showed a steady decline of the likelihood of winning a medal (Q(1):Q4(2) χ2=24.3, p=0.002).

    Figure 3
    Figure 3

    Quartile distribution of all medal winners according to sex.

    Table 3 presents the anthropometric parameters of all of the participants. As shown in figures 4 and 5, male athletes born at the beginning of the first year were significantly taller (p=0.005) and heavier (p<0.001) than athletes born at the end of the second year. No differences were found in female athletes in either height (p=0.528) or weight (p=0.112).

    Figure 4
    Figure 4

    Body weights of male and female athletes according to birth quarters.

    Figure 5
    Figure 5

    Body heights of male and female athletes according to birth quarters.

    Discussion

    The first winter YOG constituted an important showground for young athletes to present their talents and, as a consequence, to be selected for future professional careers. To our knowledge, this was the first study to examine the role of an RAE in a highly competitive and selective cohort of young athletes in winter sports. With the exceptions of ice hockey16 ,18 ,19 and alpine skiing31 surprisingly little research has been undertaken so far. Therefore, we aimed to define the role of relative age in the first YOG 2012 with regard to sex, type of sport and performance. In general, our results suggest that relative age had a highly significant influence on participation in the YOG. The observed birth-quarter distribution significantly differed from the expected even distribution, with an over-representation of athletes born in the first quarter and a clear under-representation of athletes born in the last quarter. More precisely, the risk of an RAE already existed between athletes born in Q1(1) and athletes born in Q2(1); however, the highest RAE risk was found between the relatively older athletes and those born in Q4(2). Research has shown that the greatest RAE is found in popular sports with high competition.5 ,18 ,32 ,33 Our cohort was characterised such that only one or two athletes per nation and sex were allowed to participate in each sport, leading to high selection pressure within the national nomination processes. The qualification system guarantees the participation of the best athletes in their age categories at the national level. Previous research has shown that the RAE seems to be a problem that arises at national level in youth athletes and proceeds at international events.11 ,31 Based on the current participation rate at London 2012 it can be assumed that successful young athletes use the YOG as springboard to the Olympic Games. However, only a small percentage of successful young athletes attain international sporting excellence.34

    Participation eligibility for each sport included two birth-years and the qualification process did not differentiate between the two years. In future, an equal distribution between athletes born in the first and second years should be considered.

    The importance of sex in the occurrence of an RAE has been discussed previously.12 ,32 Our results demonstrated a highly significant sex difference in the RAE with a stronger effect for male athletes. Nevertheless, for both male and female athletes, the relatively older athletes were favourably selected for participation. The results of the present study differ from other findings in which a less frequent RAE for female athletes was found.12 ,18 Helsen et al1 and Lames et al4 hypothesised that this finding occurred because the talent selection process often takes place once girls are already beyond the age of puberty and, therefore, the developmental stage with the most maturational differences between individuals has already passed. Previous research has shown that sex-related outcomes seem to result from interactions between the individual characteristics of sports, such as sport type and level.33 It has been suggested that the female variants of specific sports are not as strength-related and power-related as the male variants, and as a consequence, the maturation-related developmental lead is not as decisive. In this context, Helsen et al1 argued, that the technical components are more important among female soccer players than among male players. In our study, the large overall sample size allowed us to establish the role of sex-related RAE differences across a wide range of sport disciplines. These disciplines included team and individual sports with strength-related, endurance-related and technique-related components, minimising the individual characteristics of each sport. However, most of the female athletes participated in strength-related sports (alpine skiing and ice hockey), and the results coincided with those of Müller et al.31 Those authors showed a highly significant RAE for female participants in the Federation International de Ski (FIS) Junior World Ski Championships in alpine skiing. They also argued that the female variant of this discipline is strength-related and power-related. The similarities between their study and the present study (comparable age groups and qualification criteria) support the occurrence of an RAE in strength-related female sports.

    The sports context seems to be a major predictor of the occurrence of an RAE. To our knowledge, studies of endurance-related or technique-related sports have been less common. To compare different types of sports, we distinguished between strength-related (alpine skiing, freestyle skiing—skicross, ice hockey, short-track, bobsleigh, luge, skeleton), endurance-related (biathlon, cross-country skiing, nordic combined, speed skating) and technique-related sports (curling, freestyle skiing—halfpipe, snowboard, ski jumping, figure skating). This classification may lack specificity; however, the classification was established according to the performance predictive factors determined by previous research.35–39 Our findings support the conclusion that strength-related and power-related sports are influential factors in the occurrence of an RAE. In strength-related sports, the relatively older athletes were approximately 11.5 times more likely to take part in the YOG, whereas in technique-related sports, older athletes were approximately two times more likely to participate.

    Winning can be associated with considerable rewards, individual fame and national prestige.3 Not only did participation seem to influence RAE, but performance also did. In the present cohort, there was a clear over-representation of relatively older medal winners, and only 24.3% of the athletes born in the second year won a medal. Barnsley et al40 and Delorme et al41 reported higher dropout rates in relatively younger and less successful athletes. To equalise the year differences, the awarding of separate medals in each discipline for the first and second eligibility years should be discussed. However, awarding medals to the second eligible year will not prevent dropouts because dropouts due to RAE occur at higher levels as well.15 YOG participants are their country's top athletes and YOG participation may encourage them to have fun and train hard in future.

    Growth, maturity status, functional capacities and sports-specific skills have been suggested as playing important roles in performance among young athletes.42 It has been speculated that advantages in anthropometric (ie, weight and height) and physical (ie, strength, power and endurance) characteristics could impact those athletes born shortly after the cut-off date. The results from Raschner et al43 in alpine skiing (slalom) showed a highly significant correlation between performance and anthropometric components only in male athletes. This study showed that male athletes born in the first year of eligibility were significantly taller and heavier than the athletes born at the end of the second year, whereas in female athletes, anthropometric differences showed no tendency towards an RAE. Growth spurts in girls occur approximately two years earlier than in males;7 thus, it can be assumed that most of the 14-year-old to 19-year-old girls had already reached their peak heights and weights. The earlier maturation of girls, combined with the higher variance in the maturity status of boys, seems to be a possible explanation for the stronger RAE in male athletes.44 As already mentioned, the highest RAE was found in strength-related sports, with the highest participant rates in ice hockey and alpine skiing. Sherar et al10 reported that 14-year-old and 15-year-old ice hockey players selected for the final team were taller and heavier than the unselected players. Knowing that older athletes are heavier and taller, it can be assumed that body size, strength and power convey advantages to these athletes. In boys, peak growth is highly variable among individuals, and boys reach their peak heights and weights between 17 and 19 years of age.45 For the YOG 2012, the eligible age groups across disciplines ranged from 14 to 19 years. However, relatively younger athletes, aged 16 years, were eligible to compete in alpine skiing and ice hockey, which might have resulted in a greater variability in anthropometrics. Future classifications for eligible age groups should consider older birth cohorts for strength-related sports. When considering the links between the RAE and anthropometric components, our results were based only on chronological age. Previous research has underscored the importance of considering biological and skeletal age when discussing the RAE.5 ,10 ,46 This aspect is difficult to implement in the qualification process of the YOG; it must be undertaken early in the talent selection and development process on a national level. When discussing performance-related aspects it needs to be mentioned that the YOG brings together the world's best young athletes with equal emphasis on sport, culture and education. The athletes participate in high-level competitions striving to be the best they can. Simultaneously they act as ambassadors in their communities and encourage young people to participate in sport independent of performance levels. Within the framework of the YOG the IOC and its partners (National Olympic Committees and International Federations) also deal with drop out phenomena in youth sport and work on prevention strategies in which the RAE must be considered. The YOG 2012 attached great importance to the Culture and Education programme which focused on five themes: Olympism and Olympic values, skills development, well-being and healthy lifestyle, social responsibility and expression through digital media. The IOC together with the YOG organisers recognised the importance of social network phenomenon for the young generation in promoting the Olympic spirit.

    The YOG follow the traditional cycle of four years (Summer Games in 2010, 2014, etc and Winter Games in 2012, 2016, etc). Based on the athlete age limits athletes born in specific years of the YOG cycle are at an advantage. On the other hand, other international sports events between the YOG cycle such as the European Olympic Festivals and Junior World Championships offer young elite athletes opportunities to compete against their young international peers.

    The authors would like to state that their results should be interpreted with caution due to some limitations. The IOC regularised the number of female and male athletes to 1021 participants. We included all of the athletes in our analysis, but due to the athletes competing in 15 different sports, the sample size was occasionally small, bearing a negative impact on the statistical power of our results. In a recent study regarding the RAE, Wattie et al47 noted that there is no guarantee that phenomena observed at one point in historical time will remain at another point in time. This fact could hold true for our results regarding the RAE in the first YOG in Innsbruck. We used normative data based on the general population of Austria, Germany and Switzerland for the same birth years as the participants of the YOG. Given the multiethnic nature of the YOG participants, it could be possible that the normative data are not representative and therefore a possible limitation of this study, but finding normative data matching this unique group was not possible.

    Conclusion

    Overall, our results suggest that the selection of athletes and maturation are predictive of a large RAE among YOG participants, and they underline the importance of interventions to reduce the RAE, which should target the early maturation phase.21 Potential strategies and solutions towards resolving the RAE have been discussed extensively in the literature.2 ,5 Research has shown that changing the cut-off dates altered the subsequent participation and success profiles.5 ,48 For the next YOG 2016 in Lillehammer, one possible strategy for reducing the high RAE could be a fixed quota for each birth year within the two-year age group or to change the competition age span for all disciplines to one year. Another promising first step was made by the FIS by introducing a one year delay in starting the junior class due to the expansion of the scholarship and kids classes for the 2012–2013 season. The young athletes will gain one additional year to grow and mature before they have to compete against older athletes in FIS races. Particularly in strength-related sports, the athletes’ eligibility should be extended to the last two eligible years to minimise differences based on maturational status. Baxter-Jones44 has, in general, questioned the onset of youth competition, which has obtained new relevance due to the adoption of the YOG. To minimise the pressure of individual performance success, new team competition events have been established in many disciplines, such as alpine skiing and figure skating mixed team events. A further emphasis on team events should be placed by developing competitions with new formats.

    What this study adds

    • Selection of athletes and the maturation are predictive for the high magnitude of the relative age effect (RAE) in the first Youth Winter Olympic Games.

    • Contrary to previous findings our results demonstrate no sex differences in the RAE.

    • The high occurrence of the RAE in strength-related sports underlines the role of sport context.

    • The over-representation of relatively older medal winners confirms the relationship between performance and relative age.

    Acknowledgments

    The authors acknowledge the valuable contribution of the Organising Committee of the first winter YOG and the IOC Medical Commission for their support.

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    Footnotes

    • Contributors CR: guarantor for the study, idea for study, substantial contributions and analysis of data, wrote the article and final approval of the version to be published. LM: literature search, substantial contributions and analysis of data, made statistics and wrote the article. CH: literature search, substantial contributions and analysis of data, made statistics and wrote the article.

    • Funding Support for the study was received from the IOC.

    • Competing interests None.

    • Ethics approval The study was approved by the Institutional Review Board.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement All data were provided by the IOC and the IOC is responsible for further scientific projects regarding these data.

    • ▸ References to this paper are available online at http://bjsm.bmjgroup.com