AGC #010 - Relative age effect for coaches

Today, I’m going to teach you about the relative age effect - and how you can use it to your advantage a coach.

Malcolm Gladwell's 2008 book “Outliers” brought widespread attention to this concept, used to describe a bias toward members of a cohort or team born earlier than peers in the same group.

Most youth sports are organized into groups banded either by age or grade.

So if the cut-off is January 1, someone born in February therefore has an extra 10 months of growth over a December baby.

Relatively older players are bigger, stronger, and more coordinated, and thus get selected more often - and get the accumulative advantage of playing in better leagues, getting superior coaching, etc. The initial perceived ability gap widens.

Referencing Canadian ice hockey players in his analysis, Gladwell wrote: "The professional hockey player starts out a little bit better than his peers.

“And that little difference leads to an opportunity that makes that difference a bit bigger, and that edge in turn leads to another opportunity, which makes the initially small difference bigger still - and on and on until the hockey player is a genuine outlier."

Gladwell revisited the topic at UPenn’s Wharton Business School for his Revisionist History podcast earlier this year, as some of America’s top students attempted to guess their privilege.

Zip codes, public or private schooling, and number of siblings were all guessed, but it mostly came down to date of birth.

To Gladwell’s horror, a significant majority of these high-achieving students were anywhere from 4 to 24 months older than they might have been. Many had been held back from starting school as long as possible by parents keen to exploit this advantage.

So how can we best utilize this information as coaches?

Know who is young and old

One of the most useful pieces of information you can collect from players trying out for your team is their date of birth.

Using the first possible date of birth a player could have on your team, you can calculate the number of months younger a player is to give them a RAE score.

e.g. If the cutoff date of birth is January 1, 2010 a player was born on October 12, 2010 has a RAE of 10, while one born on March 24, 2010 has a RAE of 3.

Decide if you need to account for it

A primary question that the relative age effect throws up is whether we need to pay attention to it at all.

Is it a problem to be solved, or simply a fact of life?

Some sporting organizations have leaned into it.

New Zealand Rugby began to select its youth teams by weight rather than age group years ago.

English soccer clubs have attempted “bio-banding” - grouping by height and weight - and holding extra trials for kids born late in the selection year, to "unearth talented footballers who have previously been overlooked".

However, in their book The Best: How Elite Athletes Are Made, Mark Williams and Tim Wigmore argued that while initial barriers may be greater for later-born children, their potential for success in the long run can be higher.

"This is the paradox of the relative-age effect: it is significantly harder for later-born children to reach professional level - but, if they can make it there, they have a higher chance of reaching the peak of their sport."

Research on English cricket from 2015 backs this up.

The English Cricket Board’s player identification lead, David Court, reported that 7% of English cricketers who had made it into the system despite their late birthdays went on to play internationally, compared to only 2% of those with early birthdays.

A significant reason touted for this is the underdog effect. A later-born child faces more obstacles and adversity along the way, which presumably serves them well if they are determined enough to push through.

Apply to your environment

Whether you wish to heed the relative age effect as a coach depends on the environment you’re selecting for and your philosophy.

If you’re a coach picking a U14 team for a three-month season, then perhaps you’re not as interested in longer-term potential.

But if you are a club’s director of coaching and your remit is to have players ready for the professional game in 5 years’ time, then you likely care more about the consequences over time.

There is a trade-off between investing in a higher ceiling for long-term gain or instead chasing short-term rewards, and it’s a tough balance to strike.

So how to put RAE to use?

You could, for instance, give the information to selectors ahead of time to try reduce bias towards older, more developed players. Maybe it could be another data point to help you decide between two closely-matched players.

If you’re in the college recruitment game, and therefore trying to see which 15-year-olds might be useful players for your team when they are 18-23, then RAE is especially useful.

Given the cut-off is less about age than it is about grade in this sphere, a lot of variation is possible - players could be up to 15 months apart in age.

Do you go for the younger one with the potentially higher ceiling? Or the older one who will theoretically be more mature?

Lastly, you could wait until selections have been made (but not made public) and compare scores to see the group trend.

That’s it - Whether the relative age effect becomes just an interesting data point or something to base selection philosophy on for you, good luck with navigating it!