Long-term relative age effect: Evidence from Italian football
A vast cross-discipline literature provides evidence that — in both education and sports — the youngest children in their age group are usually at a disadvantage because of within-group-age maturity differences, known as the 'relative age effect'. This column asks whether this effect could last into adulthood. Looking at Italian professional footballers' wages, the evidence suggests that the relative age effect is inescapable.
What are the consequences of the relative age effect? For example, relatively young pupils (i.e. the youngest pupils in their age group) are more likely to be held back in school (Dixon et al. 2011) and receive lower grades (Bedard and Dhuey 2006, Ponzo and Scoppa 2014, Navarro et al. 2015). They also are more likely to be diagnosed with a learning disability (Dhuey and Lipscomb 2009) and with attention-deficit/hyperactivity disorder (Zoëga et al. 2012).
Could the relative age effect last into adulthood? Could people receive different wages because of childhood within-group-age maturity differences? Could people who suffered from adverse relative age effect in childhood be under-represented in top job positions? This column discusses some possible answers.
The path towards a long-term relative age effect
Children are usually grouped based on a relevant 'cut-off date' – in these groups, some children are relatively older than others, which causes maturity gaps and therefore performance gaps between them. For example, in some European countries, the age-grouping system in school is based on the calendar year (i.e. the cut-off date is 1 January) and children start school in September in the year when they turn six years old. In the first class, there are some children who are six before school starts (i.e. born in January-August) and others who turn six after school has started (i.e. born in September-December).
Consider the difference in maturity between children born in the two extreme months – pupils born in January are about 17% older than pupils born in December. This large maturity gap causes a performance gap – the relative age effect.
Although the relative age effect is initially caused by a pure maturity gap, social factors influence its magnitude and could provoke its persistence. In education and sport activities, children might be streamed (e.g. they are tracked into different learning/training paths) and/or selected (e.g. they are chosen to participate in optional after school classes or to play in their soccer team's starting lineup) based on their perceived skills. Furthermore, streaming and selection are affected by the level of competition between kids (e.g. there is a limited and pre-established number of spots for after school classes or in starting lineups of soccer teams).
Finally, the whole process is affected by interactions (e.g. the Pygmalion effect, see Hancock et al. 2013 – soccer trainers will provide special attention to those children whom they perceive are more talented, who as a result become more talented due to this greater attention). The process that affects the initial relative age effect can be summarised in Figure 1, taken from Fumarco and Rossi (2015).
Figure 1. Process affecting initial relative age effect
This process could lead to a possible long-lasting relative age effect, and therefore could be visible even when initial maturity differentials disappear. In particular, paraphrasing Cascio's (2008) paper – long-lasting relative age effects are likely to occur when children are streamed and selected based on perceived skills since the beginning of their training or education.
Evidence of a long-term relative age effect
Studies that investigate the existence of a relative age effect in adulthood are limited and often display discordant results. Some studies do not find evidence of a relative age effect on wages (e.g. Crawford et al. 2013, Larsen and Solli 2012). Other studies provide evidence of a negative relative age effect on wages and employment rates (e.g. Peña 2015, Black et al. 2011, Plug 2001). Results are also contradictory when the focus shifts to the relative age effect on tertiary education performance. Roberts and Stott (2015) find that students born toward the end of the selection year perform better and Peña (2015) finds that relatively older students graduate from college more frequently, whereas Kniffin and Hanks (2015) do not find any gap in the possibility to earn a doctoral degree. It is likely that one of the main reasons for not obtaining clear and coherent results on a long-term relative age effect is the lack of very detailed data.
The sports labour market provides a more suitable framework than that of the standard labour market and tertiary education system for studying long-term relative age effects because of the (often public) very rich data. Studies that use these data typically provide one result: because of streaming and selection, older athletes are over-represented in the population of athletes in any given tournament — for example, in top football leagues (Musch and Hay 1999), the Olympic Games (Joyner et al. 2013), and the NFL (Böheim and Lackner 2012).
However, the sports literature has rarely explored possible long-term effects also in terms of wages. To contribute to this limited literature, in a recent paper (Fumarco and Rossi 2015) we investigate relative age effects on footballers' wages in a very large and detailed dataset, where players are followed over several seasons, in one of the most competitive football leagues – the top Italian league, Serie A.2
Relative age effects on representativeness and on wages of Serie A footballers
Serie A 球员人数和工资的相对年龄效应
The dataset contains information on all Italian players from seven consecutive Serie A seasons, 2007-08 to 2013-14, for a total of 508 Italian footballers who have played for at least one Serie A team over these seven seasons. In Serie A there are 20 teams – at the end of each season the last three teams are relegated, while the top three teams from the second league are promoted. We focus only on Italian players because information on age-group systems of other countries is difficult to retrieve, and we do not feel comfortable assuming that foreign Serie A players trained under the same cut-off date. In fact, we know from other studies that until the mid-1990s, different cut-off dates were adopted in different EU and non-EU countries, such as, Belgium, Germany, Australia and Brazil (1 August), Japan (1 April), and Great Britain (1 September, which is still the current cut-off date).
此数据包含了2007-08到2013-14赛季间，所有508名至少为一家Serie A球队效力的意大利球员的7个连续赛季的信息。在Serie A中总共有20支球队，在赛季结束时最后三名球队会被降级，而次级联赛的前三名会被升级。我们只关注来自意大利的球员，因为其它国家球员的年龄组别很难得到，而我们不能简单假设外国运动员采用了相同的年龄分级法。事实上，从其它研究中我们得知，直到1990年代不同的欧洲和非欧洲国家如比利时、德国、澳大利亚、巴西(采用8月1日作为分隔点)，日本(采用4月1日)、英国(采用9月1日作为分隔点直至今日)分别采用了不同的年龄分隔日期。
In Italy, the cut-off date for the age-grouping system is 1 January (for complete details on the youth system, see Fumarco and Rossi 2015). In the presence of the relative age effect, players born soon after this date are expected to have enjoyed an advantage over relatively younger players born on dates approaching 31 December throughout their youth. This advantage could be reflected in at least two ways on Serie A players – distribution of players' birthdates (i.e. relatively older players could be over-represented in the population of Serie A Italian players, even if we account for the monthly birthrate of the Italian population) and wages (i.e. relatively older players could earn higher wages, which would imply persisting performance gaps). This is exactly what we have found in our study.
在意大利，年级系统的分隔日期是1月1日(更多细节可以产看Fumaraco和Rossi 2015年的文章)。在相对年龄效应的影响下，在整个青少年时期，此日期后不久出生的运动员被发现比临近12月31日出生的相对年幼的运动员更有优势。在Serie A的球员里，这一优势可能被反映在至少两个方面：球员的出生分布(即排除了意大利的出生月间差别后相对年长的球员在总意大利球员数所占中更多)和薪水(即相对年长的球员能够获得更高的薪资，这反映了其持续存在的表现差异)。而这正是我们在研究中所发现的。
Figure 2 represents the distribution of quarters of birth among Serie A Italian players.
Figure 2. Distribution of quarters of birth among Serie A Italian players
【图2:Serie A 意大利球员出生日期按季分布图】
The black dots represent average quarters of birthrates in Italy between 1965 and 1995 – this is the range of years of birth in our dataset. Clearly, players born in the first quarter are over- represented, second-quarter players are still over-represented but to a slightly lesser extent, third- quarter players are under-represented and fourth-quarter players are even more strongly under- represented. When we consider months in lieu of quarters, the trend is more striking (see Fumarco and Rossi 2015). This result seems to be strongly consistent throughout European countries, as illustrated in Poli et al. (2015) — in this study authors decide to assume uniformity in European cut-off dates.
黑点表示在我们的数据范围内，即1965到1995年间每季意大利的平均出生率。很明显，在第一季出生的球员人数与当季出生率比相对较多，第二季度出生的球员仍相对较多但比例有所下降，第三季度的球员数相对当季出生率较少，而第四季度的相对球员数明显更少。当我们用月份来代替季度时，这一趋势会更加明显(参见［Fumarco and Rossi 2015］)。这一结果似乎适用于所有欧洲国家(参见Poli等人的2015年的论文。在其研究中作者假设了欧洲所有国家使用了相同的年龄分隔点)。
Figure 3 provides average gross yearly wages (deflated at the 2013 prices level) of Serie A Italian players born in the first and fourth quarter (the other two quarters are not reported for illustrative purposes).
Figure 3. Average gross yearly wages of Seri A Italian players
Clearly, relatively older players receive higher wages than relatively younger counterparts during most of their soccer career.
Figures 2 and 3 illustrate descriptive statistics, but their insights are confirmed by statistical methods of inference (see Fumarco and Rossi 2015).
图2和图3展示了描述性的统计数据，但其洞见也被统计学推断方法所印证了(详见［Fumarco and Rossi 2015］) 。
Possible remedies and further studies
These findings provide sound evidence for a long-term relative age effect in football, in terms of both representativeness and wages, which partially satisfies our initial questions. To remediate the existence of relative age effects in the Italian football, a reform of the age-grouping system could be carried out (e.g. a shortening of the chronological distance between oldest and youngest players in the same age group). Also, football coaches could be educated on this phenomenon so they can account for it when they train children. Combatting the relative age effect in soccer is important for the sake of equity, children's happiness, and additionally because it would reduce the waste of potentially skilled (but not yet mature) relatively younger players in youth categories.
These results are only suggestive of the existence of a more general long-term relative age effect. Although the process that determines the relative age effect in sports is equivalent to that which determines the relative age effect in education, it is necessary to carry out further investigations in tertiary education system and in the more general labour market to gain generalisable conclusions on the existence of long-term relative age effects.
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1 This result has also been observed in other very competitive labour markets. Muller-Daumann and Page (2015) as well as Du et al. (2012) find evidence that people born toward the end of the selection year are under-represented among US congressmen and among CEOs for S&P 500 firms respectively. Finally, a similar result has been observed when investigating suicide rates in Japan and Canada. Matsubayashi and Ueda (2015) and Thompson et al. (1999) find that relatively younger people have a higher suicide rate.
该结果在其它竞争非常激烈的劳动力市场也被观察到。［Muller-Daumann and Page (2015)］以及［Du et al. (2012)］发现证据表明在选拔年度末尾出生的人在美国国会议员和标准普尔500强企业CEO中的比例低于应有比例。最后，相似的结果在对日本和加拿大自杀率的调查中也被观察到了。［Matsubayashi and Ueda (2015)］和［Thompson et al. (1999)］发现年龄相对小的人群有更高的自杀率。
2 To the best of our knowledge, before this study only Ashworth and Heyndels (2007) investigate the relative age effect on footballers' wages. They used a sample that covered a shorter period of time in the German first league from mid-1990s, and before the effects of the Bosman ruling fully kicked in (this ruling affected players' mobility and introduced free agency, possibly increasing competition among them).
就我们所知，在我们的研究之前只有［Thompson et al. (1999)］调查了相对年龄效应对足球运动员工资的影响。他们使用了来自德国一级联赛从1990年代中期开始的较短时期的样本，那时博斯曼法案的效果还未完全体现（博斯曼法案影响了运动员的流动性，引入了自由转会，因此可能加剧了运动员之间的竞争）。
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