Key result
First-quarter birth linked to ~2-fold higher likelihood of reaching professional soccer and baseball.
Why the study?
The mechanisms and temporal changes of relative age effects among Japanese male professional athletes across multiple sports were unclear over the past 25 years.
Observational (n=7,805)
Answers are grounded in this paper and cite their sources.
The relative age effect in Japanese professional sports has generally decreased over the past 25 years, possibly due to socio-cultural factors such as low birthrates.
Background: The mechanisms underlying the relative age effect (RAE), a biased distribution of birth dates, in sport events have been investigated for more than two decades. The present study comprised an historical analysis involving the most recent quarter-century (1993-2018) on RAEs among Japanese male professional athletes (soccer, baseball, basketball, and volleyball) to clarify how the RAEs changed over time.Methods: Birth data were obtained from 7,805 Japanese male professional athletes registered in 1993, 2001, 2010, and 2018. The athletes were divided into four groups based on their month of birth: quartiles Q1 (April–June), Q2 (July–September), Q3 (October–December), and Q4 (January–March of the following year). In addition, based on the data in 1993 for soccer and baseball and in 2010 for basketball and volleyball, the expected numbers of players were calculated in 2001, 2010, and 2018 for soccer and baseball, and 2018 for basketball and volleyball.Results: Significant RAEs were observed among soccer and baseball players in 1993, 2001, 2010, and 2018, and strong tendencies of RAEs were found among basketball and volleyball players in 2010 and 2018. The magnitudes of the RAEs in soccer, baseball, and volleyball decreased over time, but not in basketball.Conclusion: The exact reasons for the decreasing or unchanging RAEs among these professional players remains unclear, but socio-culture factors, such as low birthrates and the popularity of sports in Japan, might be related to the changing RAEs.
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Sasano et al. (2020) conducted an observational in Relative age effect in professional sports (n=7,805). Birth in the first quarter (April-June) vs. Birth in the fourth quarter (January-March) was evaluated on Relative age effect (Q1 vs Q4 birth quarter) in professional soccer players in 2018 (OR 2.06, 95% CI 1.82-2.34, p=<0.001). Being born in the first quarter of the selection year was associated with a significantly higher likelihood of becoming a professional athlete in soccer and baseball, though the magnitude of this relative age effect decreased over the 25-year study period.
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