The “Relative Age Effect” in Sports

outliers-11Posted by Tyler Bradstreet

Last night, I came across a paper I wrote in an undergraduate sociology class, and I thought it was interesting enough to share some of it with you all. The topic comes from the book:

Outliers by Malcom Gladwell
Chapter One – The Matthew Effect

(*Note – my writing wasn’t as good back then, and I definitely didn’t consistently follow APA guidelines!)


In Chapter One (“The Matthew Effect”) of Outliers, Malcolm Gladwell (2008) writes about Canadian psychologist Roger Barnsley, one of the first to draw attention to the relative age effect phenomenon. Relative Age Effects (RAEs) describe attainment inequalities as a result of interactions between biological age and age-grouping procedures.

Barnsley began looking at this phenomenon after his wife brought it to his attention at a Canadian Junior Hockey League game. Barnsley’s wife noticed that there were an incredible number of January, February, and March birth dates (2008:22). After noticing this, he went home and researched the birth dates of professional hockey players in the National Hockey League. He found the same pattern in the birth dates. The more he looked, the more he came to believe that what he was seeing was not a chance occurrence but an iron law of Canadian hockey: in any elite group of hockey players, the majority of the top players will have been born between January and March (2008:23).

Gladwell states that the explanation for this is quite simple: The eligibility cutoff age for age-class hockey is January 1 (2008:24). Therefore a boy who turns ten on January 2 could be playing on the same team as a boy that does not turn ten until December 31. That twelve-month age gap will more than likely have an enormous difference in their physical maturity. This age gap has tremendous advantages.

The “best players” make the all-star teams, and the “best players” are usually the bigger and more coordinated players, which can be attributed to their benefit of the few extra critical months of maturity. Once on these teams, the players get better coaching, better teammates, more practice, and play three times as many games than those not on the all-star teams.

Gladwell states that at first, this advantage is not as distinctive but over a succession of several years, the advantages that come from playing on the all-star teams, which came from being older, become glaringly obvious; The player really is better now, and not just older (2008:25). Barnsley states that this “skewed age distributions” exist whenever selection, streaming, and differentiated experience occur.  When a decision is made about who is talented and who is not early on and they are separated, then the talented are provided with a “superior experience,” which in turn causes the huge advantage over the people born closer to the cutoff date.

Gladwell states that baseball leagues in the U.S have similar relative age effects as the Canadian hockey leagues (2008:26). In baseball, the cutoff date is July 31, which is the reason why an overwhelmingly amount of players in Major League Baseball are born in August. The bottom line is that those who are successful are the ones who receive the special opportunities that lead to further success, and in the realm of little leagues/junior leagues, it is the biggest/oldest nine and ten year olds that receive the most coaching, practice, and playing time.



Gladwell calls the relative age effect an “accumulative advantage,” that starts off with coaches confusing maturity with ability (2008:30-31). This starts a “progressive effect” that puts the older players in position to improve more, year after year. I find it amazing that an “arbitrary date” has such a profound effect on sport development. I believe this is a topic that needs to be analyzed in more depth because of how crucial RAEs are to sporting success as well as successful individual growth and development.

In the end…

Is there really a viable solution to circumvent the problem it causes not just in sports, but in academics as well? Or is it inevitable?

To provide some more interesting information on this issue, here’s another excerpt from the paper regarding a potential moderating factor that would trump RAEs.


The article I reviewed was “Relative Age Effects are a developmental problem in tennis: but not necessarily when you’re left-handed!” (Loffing, Schorer, and Cobley, 2010).  The purpose of this journal article was to examine whether an additional individual characteristic (in this case, handedness) could possibly circumvent the RAE problem. Loffing, Schorer, and Cobley state that relative age is the chronological age differences between individuals within annually age-group cohorts, and that annual-age groups are employed by most sport governing bodies as an attempt to create homogenous competition possibilities for the individuals and teams (2008:19).

However, as we have seen in Gladwell’s book, these arbitrary dates have a significant effect and do not actually create homogenous competition possibilities.  Loffing et al. are attempting to see if there are other moderating factors (i.e. individual characteristics), which could account for variability in the effect size of RAEs (2010: 20). One characteristic that has been rarely looked at is laterality, or handedness. Being left-handed is rare and valuable in sports. The general consensus is that roughly 10% of people report writing or throwing with their left hand.

SPT (Shebest)However, in sports, left-handers are constantly over-represented in sports. It has been proposed that this may be due to a lack of visual familiarity with left-handed actions, which in turn gives left-handers an advantage because their opponents are unable to perceive and anticipate particular outcomes (2010: 20). Loffing et al. used tennis as the sport in their study because there are no positions that offer advantages for left-handers (i.e. right wing in soccer or first base in baseball). Therefore, if they can find variability in RAEs between left- and right-handed players in tennis, then this might be attributed to handedness dependent advantages.

Loffing et al. listed the handedness and birth date for the top 500 of the ATP (Association of Tennis Professionals) between 2000-2006. The cut off date is January 1in tennis. Their results indicate that there is in fact a significant over-representation of left-handers in tennis (85.56% right, 13.44% left). There was a significantly higher percentage of right-handers born in the first half of the year, where as for left-handers there was a slightly reversed trend (2008: 22). Even though there effect sizes were small, there is at least some trend to suggest that RAEs affect left-handers less than their right-handed counterparts (2008:23).

The fact that the distributions of birth dates in Loffing et al.’s study were not as significant as previous studies may be due to tennis not being a sport that has any positions that are advantageous for left-handers (such as baseball or soccer). If they would have used one of these sports, the results would probably have been significant, but because there was at least some trend that RAEs affect left-handers less in a sport without advantageous positions for them suggest that there may in fact be some truth behind the idea of left-handedness circumventing the RAE problem. In the end, what does appear optimistic is that relatively younger left-handers are able to overcome potential disadvantages.


So, as a fellow left-hander, this is good to hear. Now, I just wish the same was for being short!

Some interesting food for thought… I hope you enjoyed it. Any thoughts?

Until next time…

Kind Regards,

Tyler C. Bradstreet
Master’s Student: Sport and Exercise Psychology
Teaching Fellow: Department of Kinesiology, Health Promotion, and Recreation
Sport Psychology Consultant: Center for Sport Psychology and Performance Excellence
University of North Texas: Denton, TX

1.) Gladwell, Malcolm. 2008. Outliers: The Story of Success. New York: Little Brown.
2.) Loffing, F., Schorer, J., & Cobley, S. P. 2010. “Relative Age Effects are a developmental problem in tennis: but not necessarily when you’re left-handed!” High Ability Studies. 21:19-25.


7 thoughts on “The “Relative Age Effect” in Sports”

  1. Hello,

    Being left-handed is an advantage in tennis. As a right-handed player, I prepare my game by playing to my opponent’s weaker ground stroke, generally the backhand. If I am playing a right-handed opponent, I am playing most of my ground strokes to my (as I see it) right side of the court. – that is, to my opponernt’s backhand. However, if my opponent is left-handed, my shots are being played to his forehand – the stronger groundstroke. I am speaking in geeneralities as any player may have a stronger backhand than forehand, but a right-handed player trains his game to play to the opponent’s weaker stroke. This is why many right-handed players develop the “inside-out” forehand initiated by Lendl.

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