If you group them by month of birth, something interesting happens.

Do you see it? I'll give you a hint.

There are significantly more players born in the first 6 months than in the last 6 months of the year.

This is caused by a phenomenon called the relative age effect.

I'll explain what that means.

Let's say it's December 31st of 2022.

Two friends meet for a birthday party.

Red was born on january 1st 2004.

Blue, the birthday boy, was born on December 31st and just turned 18.

Right now they are both 18 and you wouldn't notice the differences between them.

Afterall, Red is only 6% older than Blue.

However, if we travel back in time it's a different story.

Let's go back to their first day of primary school.

It's now September 1st of 2010.

Even though the difference between their ages is still 11 months and 30 days, the relative age difference increased.

Red is now 18% older than Blue.

At this age, the 11 additional months he had to grow make a difference and you can see it.

He's taller, stronger and mentally more developed, which gives him an advantage in sports and school.

This is known as relative age effect: people born earlier in the school or sports year tend to perform to a higher level than those born at the end of the year.

But if we travel back to 2022 these differences should disappear. right?

Well, not really.

Research shows us is that even when we become adults, people who were older than their peers during childhood still have an advantage in sports, education and even in positions of leadership.

The small advantages at an early age can build up into bigger advantages in adulthood.

This is known as the Matthew effect, aka "The rich get richer, the poor get poorer".

What is a small advantage at the start can develop into a bigger advantage later on.

The point of this video is to talk about how the relative age effect can impact success in education, sports, career and what we can do about it.

Let's start with Sports.

In most sports, children are grouped based on their calendar year of birth.

On average, children born earlier in the year are taller, stronger and faster.

Therefone, an older child will have a higher chance of being selected by the coach to play.

Being selected to play, means the child gets more experience, becomes better and ends up with higher chances of becoming a professional athlete later on.

It's the Matthew effect.

The older player is picked because he is better, and then ends up becoming better with time because he was picked, apparently validating the early decision of the coach.

It's a self-fulfilling prophecy.

There's plenty of research about the relative age effect in sports.

There's studies in football, baseball, ice hockey, tennis, you name it.

I decided to share the findings of this study in Sweden.

I chose it because it's quite recent and, honestly, because it's the first result on Google.

Their conclusions: the birthdate distributions were consistently skewed for every individual sport they investigated.

They looked at different sports and analyzed the birthdays of every athlete.

They grouped them in blocks of 4 months (also known as tertiles) and they compared the actual number of athletes per tertile against the numbers that you would expect from looking at the births of the population in Sweden.

The y-axis shows the ratio between these two numbers.

In other words, if the ratio is higher than 1, that means there is an abnormally high number of athletes born in those months.

They looked at 14 to 17 year old athletes in Athletics and they got these results.

Take a second to see what this means.

There's 27% more athletes born in the beginning of the year than what would be normal for the Swedish population, and 28% fewer at the end of the year.

These are big gaps.

If the results are accurate this means that teenagers born in the first tertile are 74% more likely to become athletes than those born in the last tertile.

The authors frame the results in way that might give a better picture of what this means.

In theory, these gaps represent the "Missed Stars".

Teenagers that had the potential but never made it as athletes because of the month they were born in,

whereas this gap represents the athletes that are quote "Not Talented" - teenagers that wouldn't have made it as athletes if the rules were even.

The gap is not as big for older age groups, but it's still there.

They also found similar results in cross-country skiing and alpine skiing

The authors even mention that the relative age effect can have a negative impact on public health because it can reduce the lifetime levels of physical activity.

They even found a reverse relative age effect in E-sports for some age groups.

They suggest the hypothesis that relatively younger children are more likely to dropout from physical sports and focus more on other hobbies, like playing video games.

One import note: In most investigated sports, the birthdate distribution was not correlated to the performance of the adults.

In other words, being born early means you get a higher chance of being selected to play when young.

But once you're older and you're part of those selected, it doesn't really matter.

Some studies even mention the underdog hypothesis - since younger children are less physically mature, they must possess or develop superior skills to be competitive.

The relative age effect is also present in education.

Each country has their own criteria to determine to which school year students belong.

In some countries, like Portugal, where I'm from, the cut-off date is December 31st.

This means January kids are the oldest in class.

In the Southern Hemisphere, February and March are common cut-off months, whereas August and September are more common in the Northern Hemisphere.

No matter what cut-off date we choose, we're going to end up with a group of students with older and younger children.

Older children are cognitively more developed.

As a result, they score higher marks on average, and, by the time they end school, they can be more likely to attend higher education in academic schools over vocational schools.

Once again, the Matthew effect.

The skills learned by the older students early in school can build up and increase their advantage when applying to university later on.

There is plenty of research pointing to a relative age effect on education.

For example, this study looked at the performance of Dutch teenagers in school for each month of birth.

In the Netherlands, October kids are the oldest of the class.

The authors analyzed the percentage of students that had to repeat a grade and, as expected, the younger students struggled the most.

They also checked the percentage of students that skipped a grade and, once again, the older students performed the best.

So, we came to the conclusion that the relative age effect has an impact in sports and education.

We've also seen how small early advantages can build up to bigger advantages later on

Therefore, it's not a surprise that this can also affect your career.

There are studies in the US Senate and House of Representatives, in Finish Politics, and even in the corporate CEOs of S&P 500 Companies.

These studies all have similar conclusions: professionals who were born in late months of the school calendar are underrepresented in positions of leadership.

So, what can we do to solve the relative age effect?

Well, unfortunately if you're watching this video, it's probably a bit too late to do much for yourself.

However, what what we can is to try to reduce this effect on our younger generations.

Research on this topic often mentions the same point: We should separate children based on abilities, not on their age.

In sports, children should be selected based on skill, not on size or strength.

And In schools, children should be allowed to learn at their own pace.

Finally, we should educate coaches and leaders on the consequences of the relative age effect, which is also the point of this video.

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