Relative age effects and the youth-to-senior transition in Italian soccer: the underdog hypothesis versus knock-on effects of relative age

Born to win? Investigating the relative age effects in the big five European women's football leagues

Introduction

This study examines the presence of the Relative Age Effects (RAEs) among players in the top five European women's football leagues during the 2023/24 season.

Methods

A total of 1,634 professional players from the Women's Super League (England), Liga F (Spain), Frauen-Bundesliga (Germany), Serie A Femminile (Italy), and Division 1 Féminine (France) were analyzed. Birth date distributions were assessed to determine the prevalence of RAEs both collectively and within each league.

Results

Poisson regression analyses revealed significant overall RAEs, with a higher proportion of players born in the first semester of the year. Individually, significant RAEs were found in England, Spain, Italy, and France, while Germany did not exhibit statistically significant effects. When analyzed by playing position, significant RAEs were observed among goalkeepers and midfielders, but not among defenders and forwards.

Discussion

These findings highlight the ongoing influence of RAEs in elite women's football and underscore the need for strategies to mitigate its impact on talent identification and player development.

The Royal Netherlands Football Association (KNVB) relative age solutions project-part one: a call to action

Introduction

Despite its widespread prevalence in youth soccer, there seems to be no widely implemented intervention to moderate or overcome Relative Age Effects (RAEs). The purpose of this study was a call to action for stakeholders to propose relative age solutions to the Royal Netherlands Football Association (KNVB).

Methods

The call to action consisted of a standardised, open-access questionnaire that contained questions focussed on: (a) the mechanisms of the proposal, (b) hypothesised effects, and (c) reference to empirical findings.

Results

Following the initial screening of 185 submissions, a total of 143 eligible proposals were included. Each proposal was categorised by two project members based on a taxonomy to classify different approaches designed to reduce RAEs by: (a) altering the behaviour of observers, (b) implementing rules when selecting teams, or (c) adjusting competition structures. From this, 13 lower-order independent solutions were categorised.

Discussion

Interestingly, whilst no new suggestions outside the existing literature were proposed in any of the submissions, only two have been empirically tested in soccer. Overall, the results present a useful first step in identifying possible relative age solutions. Due to the number of proposed solutions and their anecdotal nature, the next step for the KNVB was to utilise the knowledge of experts in the field via an adapted e-Delphi study to identify the most effective and feasible solutions to implement in practice (Part Two).

Relative age effects in European soccer: their association with contextual factors, impact on youth national teams' performance, and presence at the senior level

Introduction

Soccer systems promote early identification and specialisation practices to satisfy short- and long-term goals-both from sporting performance and financial gains perspectives. In this context, players are (de)selected based on observed performance level and on their ability to conform to given organisational demands, leading to the proliferation of selection biases, such as relative age effects (RAEs), which research has shown to influence both developmental experiences and senior career achievements. Accordingly, this study aims to: (a) investigate the magnitude of RAEs among youth national teams competing in the UEFA U17 European Soccer Championship, and their associations with teams' final ranking, (b) examine whether RAEs magnitude could be linked to cultural and contextual factors, and (c) further explore RAEs at senior level.

Methods

Birth quarter (BQ) distribution of youth national teams (n = 80) that competed in one of the five editions (2018, 2019, 2022, 2023, and 2024) of the UEFA U17 European Soccer Championship was recorded. Teams were classified based on their country of origin, RAEs magnitudes, final ranking in the tournament, FIFA points, and national population. Furthermore, the BQ distribution of senior national teams (n = 24) that competed at the 2024 UEFA Senior European Soccer Championship was recorded.

Results

Chi-square statistics revealed BQ1s were overrepresented at the U17 level (p < 0.001) and showed teams exhibiting low RAEs magnitudes recorded the highest likelihood (odds ratio: 5.67) of finishing the tournament in the bottom four positions. Correlation analyses recorded small to moderate positive correlations between RAEs magnitude and national population (.25) and FIFA points (.33). Further chi-square statistics revealed BQ1s continued to be overrepresented at the senior level, albeit with a weaker effect (p < 0.001). However, when the senior BQ distribution was compared to the expected distribution taken from the U17 population, this recorded more BQ4s and fewer BQ1s than expected (p < 0.001).

Discussion

The findings presented the focus on youth success, the increased talent pool size, and the competition for selection interact to reiterate RAEs' prevalence in European soccer. Moreover, they highlighted initial RAEs define players' journey within the soccer system, whereby relatively older players remain overrepresented at the senior level, albeit to a weaker and lesser extent.

Relative Age Effects and Place of Early Development Constrain Male Youth Italian Swimmers' Developmental Experiences

Italian swimming emphasizes the early specialization of selected children from approximately 6 to 7 years old. Such an approach often leads to selection biases (i.e., birth advantages), which may undermine swimmers' development and progression through the talent pathway. Accordingly, this study aimed to: (a) explore the presence of birth advantages at the annual Italian national age-group competition by observing the birth quarter (BQ) and place of early development (PED) distribution of 514 U15 swimmers; and (b) investigate how birth advantages affect swimmers' ability to maintain their national status by comparing the BQ and PED distributions of 555 U17 national-level swimmers to the expected values (i.e., U15 distribution). Chi-square statistics for the U15 revealed an overrepresentation of BQ1s and swimmers developing in north and central Italy (p-values < 0.0001). In contrast, the U17's BQ (p < 0.001) and PED (p = 0.01) distributions appeared skewed compared to the U15, favoring swimmers born in BQ3 and BQ4, and swimmers developing in north Italy (odds ratios: 1.69, 1.76, 1.39 respectively). The findings highlighted that cultural-contextual features of the environment shape Italian youth swimmers' development and their progression through the current talent pathway.

Career trajectories, transition rates, and birthdate distributions: the rocky road from youth to senior level in men's European football

This study aimed to assess youth-to-senior transition rates, quantify the magnitude of relative age effect (RAEs), and evaluate how RAEs affect these transitions in 9,527 men's national football players of England, France, Germany, Italy, and Spain. Regardless of national team, only -15%, 25%, and 40% of U17, U19, and U21 players successfully transitioned to the senior team, respectively, whilst -14%-24% progressed to senior level without being selected during youth. Data suggested a skewed birthdate distribution favouring relatively older players at U17, U19, and U21 levels across all countries, whereas RAEs were also present in England, Italy, and Spain at senior level. Youth-to-senior transition rates were modulated by birthdate at U17 and U19, whereby Q4 players were -2 and 1.5 times more likely to successfully transition at senior level than Q1 players, respectively. Selection at youth international level does not guarantee selection at senior level, but does make it more likely. Moreover, relatively younger athletes are disadvantaged in youth categories, although are more likely to transition to senior level once they have entered the pathway.

Relative Age Effect Analysis in the History of the Ballon d'Or (1956-2023)

Ballon d'Or is the most important individual award in football, and is a significant measure of excellence. From our knowledge, this is the first study that explored the relative age effect (RAE) throughout the history of the Ballon d'Or. A total of 1899 football players nominated for the award from the first edition in 1956 to the most recent edition (2023) were analyzed. To assess the RAE, the birthdate distributions were categorized into four trimesters. The comparison involved correcting for the uniform distribution using chi-square analysis, with Cramer's V serving as a measure of effect size. Standardized residuals were computed to identify quarters that exhibited significant deviation from the expected values. Odds Ratio and 95% confidence intervals were used to identify discrepancies between trimesters. The results indicated a pronounced presence of an RAE at the global level. However, the longitudinal analysis revealed variations in the behavior of the RAE over time. In the initial decades, there is an overrepresentation of players born in the last months of the year. Subsequently, there is no discernible RAE. In the most recent decades, there has been a clear resurgence of RAE, with an overrepresentation of players born in the first quarters of the year.

Birth Advantages in Male Italian Soccer: How They Influence Players Youth Career and Their Future Career Status

Soccer organizations generally adopt deterministic models within their talent pathways. In this framework, early ability and results are emphasized, leading to selection biases, such as birth advantages (i.e., relative age effects and birthplace effects), which research has shown affect both early developmental experiences and continued sporting involvement. Accordingly, this study aimed to (a) provide further test of birth advantages in Italian youth soccer by exploring the birth quarter (BQ) and birthplace (BP) distribution of 1050 male Italian players born between 1999 and 2001 who competed in the national U17 championship throughout the 2015-16 season and (b) investigate how birth advantages influenced selected players' future career status. Chi-square goodness-of-fit tests revealed early born players, and players born in North Italy were overrepresented at the youth level (p-values < 0.0001). Successive prospective analysis revealed only 18% of players developed into professional-level soccer players. Chi-square tests of independence indicated that players' BP was associated with their future career status (p < 0.0001), whereas their BQ was not (p = 0.459). Odds ratios showed players born in North Italy were five times more likely to complete the youth-to-senior transition than those born in South Italy. These findings highlighted environmental factors influence Italian players' early developmental experiences and their future career status.

Is There a Relative Age Effect among the Most Successful Track and Field Athletes?

The prevalence of the Relative Age Effect (RAE) was studied among medalists from the World Athletics Championships at U18, U20 and Senior age groups and from the Olympic Games from 2000 to 2022. The specific events examined were the 100, 200, 400, 800, 1500, and 3000/5000 m, the long jump, the triple jump, the high jump and the pole vault. Dates of birth from 1,858 outdoor track and field athletes were analysed and further divided into four groups according to the quartile of birth. The RAE was found to be widespread among athletes of both sexes in U18 and U20 age groups in all examined disciplines. There was no difference between the most successful U18 and U20 athletes (p = 0.52). Among senior athletes of both sexes, this effect was not detected and the number of "late-born" athletes in this age group was higher than athletes born in the first three quarters. The prevalence of the RAE across the four groups of events was found in U18 and U20 age groups. Additionally, within each age group, the difference among events was statistically significant. In most successful track and field athletes, the RAE is only significant in U18 and U20 age groups. In senior athletes, the number of "late-born" athletes is significant while RAE disappears. These data may be considered when assessing the athletic potential of an individual athlete.

Effects of the New COVID-19-Induced Rule on Substitutions and Performance in Italian Elite Soccer

COVID-19 has resulted in widespread changes, including within the realm of sports. Professional soccer has adapted by allowing more substitutions, leading to tactical adjustments and potential physical benefits. Accordingly, this study analyzed the impact of the new rule in Italian top-level soccer, focusing on substitution patterns and performance differences between the pre-COVID (2017-2018, 2018-2019 seasons) and post COVID (2020-2021, 2021-2022 seasons) eras. As such, publicly available data from 1520 matches (760 matches per era) were recorded. The sample included matches played from 40 Italian top division teams in both the pre- and post-COVID eras. Analyses confirmed substitutions follow a consistent temporal pattern throughout the match in both eras, highlighting a slight difference in second-half management, and showed the new rule is still not used to its full potential, thus raising concerns about teams' financial strength, as not all managers possess "deep benches" (i.e., a large number of top-level players available to play). Further analyses revealed a statistically significant increment (p = 0.002) in the quantity of collectively produced sprints in the post-COVID era compared to the pre-COVID one. The results from this study emphasize the need to carefully address sprint preparation and repeated sprint abilities, also considering factors such as the number of substitutes and their skill level.

Junior to senior transition pathway in Italian Football: The rocky road to the top is not determined by youth national team's selections

Football is a popular sport, but little is known about the youth-to-senior transition rates in elite players, particularly in large and successful countries. This study aims to investigate the youth-to-senior transition rate in the Italian national football team, both prospectively and retrospectively, and to explore if Relative Age Effects (RAEs) affect this transition. Data from 885 players selected in youth and senior Italian national teams between 2000 and 2021 were included in the study. For each player, the birthdate and the number of selection in Under 16, 17, 19, 21 and senior team was considered. The transition rate was determined by the number of youth players competing in the Senior National team (and vice versa), whilst birth quarter (Q) distributions with a chi-square goodness-of-fit test. Prospectively, the transition rate increased as age increased (i.e., from ~20% in U16 to ~50% in U19). Retrospectively, less than 10-20% of youth players were subsequently selected for the senior team. Data revealed a skewed birth date distribution in all age groups, and the RAEs magnitude decreased when age increased (i.e., ORs for Q1 vs Q4 was ~ 9 in U16 and ~ 1.7 in senior teams). Nevertheless, the RAE magnitude was smaller for successfully transitioned players. In conclusion, most players in the senior team were not previously selected for youth teams suggesting that junior international experience may not be a prerequisite for later success. Moreover, while the birthdate strongly influences the selection of youth national teams, its impact is less evident in the youth-to-senior transition.

Relative age effect reversal on the junior-to-senior transition in world-class athletics

The relative age effect (RAE) is a selection bias resulting from the interaction between the selected dates and birthdates. Nevertheless, the impact of birthdate on the junior-to-senior transition in international track and field is unclear. This study aimed to quantify the RAE's magnitude and test if birthdate affects the junior-to-senior transition rate. The birthdate and performances of 5,766 sprinters (female: 51.0%) and 5,863 jumpers (female: 45.9%) were collected. Elite athletes (operationally defined as the World's all-time Top 200, 100 and 50 athletes) were identified according to Under 18 and Senior categories. Skewed quartile distributions were observed in the Under 18 (effect size ranged = 0.15-0.10) but not in the Senior category. RAE magnitude increased according to performance level (i.e., from Top 200 to Top 50) and was higher in males than females. Relatively younger athletes showed significantly higher transition rates with a higher chance of maintaining top level in the senior category (odds ratio (OR) ~ 1.64). The probability of maintaining success was lower for sprinters than jumpers (OR ~ 0.70), influenced by decade of birth and continental place but similar for male and female athletes. Data corroborate that relatively younger athletes are disadvantaged in the junior category but advantaged when transitioning to the senior category.

Age and Maturation Matter in Youth Elite Soccer, but Depending on Competitive Level and Gender

This study aimed to explore the relevance of the relative age effect (RAE), maturity status and anthropometry, and their influence on coaches' assessment of players' performance, analyzing both genders and different types of academies (elite vs. non-elite). The sample included 603 soccer players (385 male), from the under 12 (U12), under 14 (U14) and under 16 (U16) categories, belonging to elite and nonelite teams. Coaches' assessment of players' performance, chronological age, anthropometric characteristics, maturity offset (MO) and peak height velocity (PHV) were registered. Our results showed that RAE was present in both genders within the elite, but not in the nonelite academies. Early maturity players were overrepresented in the male elite, but not in the female academies. No relationship was found between RAE and anthropometry in male elite academies. Male elite players showed better anthropometric characteristics than nonelite players, while this pattern of results was not found for female players. The coaches' assessment on players' current performance was not influenced by the chronological age nor anthropometry, but it was linked to the PHV. Coaches from nonelite academies rated better in current assessment of performance the taller players. Our findings suggest that maturity status and RAE play an independent and important role in the talent selection process.