University of Split, Faculty of kinesiology, Split, Croatia.
University eCampus, Novedrate, Italy.
PLoS One. 2018 Aug 8;13(8):e0201795. doi: 10.1371/journal.pone.0201795. eCollection 2018.
The main objective of this research was to determine the existence of relative age effect (RAE) in five European soccer leagues and their second-tier competitions. Even though RAE is a well-known phenomenon in professional sports environments it seems that the effect does not decline over the years. Moreover, additional information is required, especially when taking into account second-tier leagues. Birthdates from 1,332 first-tier domestic players from France, England, Spain, Germany and Italy and birthdates from 1,992 second-tier domestic players for the 2014/2015 season were taken for statistical analysis. In addition to standard statistical tests, the data were analyzed using econometric techniques for count data using Poisson and negative binomial regressions. The results obtained confirmed a biased distribution of birthdates in favor of players born earlier in the calendar year. For all of the five first-tier soccer leagues there was an unequal distribution of birthdates (France χ2 = 40.976, P<0.001; England χ2 = 21.892, P = 0.025; Spain χ2 = 24.690, P = 0.010; Germany χ2 = 22.889, P = 0.018; Italy χ2 = 28.583, P = 0.003). The results for second-tier leagues were similar (France χ2 = 46.741, P<0.001; England χ2 = 27.301, P = 0.004; Spain χ2 = 49.745, P<0.001; Germany χ2 = 30.633, P = 0.001; Italy χ2 = 36.973, P<0.001). Econometric techniques achieved similar results: estimated effect of month of birth, i.e., long-term RAE on players' representativeness, is negative (statistically significant at the 1% level). On average, one month closer to the end of the year reduces the logs of expected counts of players by 6.9%. Assuming this effect as linear, being born in the month immediately before the cut-off date (i.e., December/August), reduces the logs of expected counts of players by approximately 75.9%. Further, ID (index of discrimination, that is, the ratio between the expected counts of players born in the middle of the first and the twelfth month of the selection year) is 2.13 and 2.22 for the first- and second-tier, respectively. In other words, in the top five European first-tier and second-tier leagues, one should expect the number of players born in the first month of the calendar year to be twice the number of those born in the last month. The RAE in the second-tiers is the same as in the first-tiers, so it appears that there is no second chance for later born players. This reduces the chances to recover talented players discarded in youth simply because of lower maturity.
本研究的主要目的是确定五个欧洲足球联赛及其二级联赛中是否存在相对年龄效应（RAE）。尽管 RAE 是职业体育环境中众所周知的现象，但它似乎并没有随着时间的推移而减弱。此外，还需要额外的信息，尤其是在考虑到二线联赛时。统计分析中使用了来自法国、英格兰、西班牙、德国和意大利的 1332 名一线国内球员和来自这五个国家的 1992 名二线国内球员的出生日期。除了标准的统计检验外，还使用泊松和负二项回归等计量经济学技术对数据进行了分析。所得结果证实了出生月份有利于年初出生的球员的偏态分布。对于所有五个一线足球联赛，出生月份的分布都存在不平等（法国 χ2 = 40.976，P<0.001；英格兰 χ2 = 21.892，P = 0.025；西班牙 χ2 = 24.690，P = 0.010；德国 χ2 = 22.889，P = 0.018；意大利 χ2 = 28.583，P = 0.003）。二线联赛的结果相似（法国 χ2 = 46.741，P<0.001；英格兰 χ2 = 27.301，P = 0.004；西班牙 χ2 = 49.745，P<0.001；德国 χ2 = 30.633，P = 0.001；意大利 χ2 = 36.973，P<0.001）。计量经济学技术得出了类似的结果：出生月份的估计效应，即对球员代表性的长期 RAE 为负（在 1%的水平上具有统计学意义）。平均而言，接近年底的月份会使球员的预期数量减少 6.9%。假设这种效应是线性的，那么在截止日期前一个月（即 12 月/8 月）出生，会使球员的预期数量减少约 75.9%。此外，ID（鉴别指数，即选择年份中第一个和第十二个月出生的球员的预期数量之比）分别为 2.13 和 2.22，适用于一线和二线联赛。换句话说，在欧洲前五大一线和二线联赛中，人们应该期望在日历年初出生的球员数量是在最后一个月出生的球员数量的两倍。二线联赛中的 RAE 与一线联赛相同，因此似乎后来出生的球员没有第二次机会。这降低了因成熟度较低而放弃青年时期有天赋球员的机会。
