Key result
Significant relative age effects were observed among Japanese professional soccer and baseball players from 1993 to 2018, though the magnitude of these effects decreased over time.
Observational (n=7,805)
The relative age effect among Japanese professional athletes in soccer, baseball, and volleyball has decreased over the past 25 years, possibly due to socio-cultural factors.
Answers are grounded in this paper and cite their sources.
May warrant monitoring in youth athlete pathways; leaves open socio-cultural drivers of temporal declines.
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 7805 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 remain unclear, but socio-cultural 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 Professional sports participation (n=7,805). Birth in the first quartile of the academic year (April-June) vs. Birth in the fourth quartile (January-March) was evaluated on Relative age effect (biased distribution of birth dates) (p=<0.001). Significant relative age effects were observed among Japanese professional soccer and baseball players from 1993 to 2018, though the magnitude of these effects decreased over time.
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