Key result
First-quarter birth linked to ~106% higher odds of becoming a professional Japanese athlete.
Why the study?
The mechanisms and temporal changes of relative age effects among Japanese male professional athletes across multiple sports over 25 years were unclear.
Observational (n=7,805)
The relative age effect among Japanese professional athletes has decreased over the last 25 years in soccer, baseball, and volleyball, possibly due to socio-cultural factors.
May indicate modifiable selection biases via socio-cultural shifts; leaves open mechanisms and applicability beyond Japanese soccer/baseball.
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.
No takes yet. Share an insight, caveat, or question.
Sasano et al. (2020) conducted an observational in Relative age effect in sports (n=7,805). Birth in the first quartile (April-June) vs. Birth in the fourth quartile (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 quartile of the academic year significantly increased the odds of becoming a professional soccer or baseball player in Japan, though the magnitude of this relative age effect decreased from 1993 to 2018.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: