More on the Relative Age Effect in the US Development program

"For everyone who has will be given more, and he will have an abundance. Whoever does not have, even what he has will be taken from him." Matthew 25:29

In my last post I looked at the birth months for a few of the Academy teams.  This shows that the age-cut is skewing the birth month distribution.  The Matthew Effect says that those players with an advantage, in this case being older for their age group, will advance faster in their skills due to the extra play time and coaching because they would be more likely to be the 'stars' being the eldest on the team.  What's interesting is that US players will mainly have been affected by a different cut-off during their U11-U14 years before they try-out for an academy team at U15/16.  Most US players would have been playing under a system with a August 1 cut-off for their U11-U14/15 years.   If the Matthew Effect is operating, we would expect to see an overabundance of August relative to July birth months on the Academy teams.  August boys were the eldest in their age group while July boys were the youngest---however they are basically the same age.  Now, keep in mind that July boys might have started formal soccer a year earlier (being born in July), so perhaps this extra year (at age 8-10) would offset the disadvantage of being the youngest.

For this analysis, I used all players on the US Development Academy teams whose citizenship was listed as USA.  No players who listed another country or dual citizenship were included.  The following shows the birth month for the U15/16 players born in 1996 (U16).  I left out the 1997's since my previous post suggested that their birth months is strongly skewed to the first quarter.  I also looked at the U17/18 players, broken out for birth year 1997 (U17) or 1998 (U18).

The following plot shows the result.  Y-axis is the frequency of the birth month.  The thin line is the median expected frequency.  It's wavy because the months don't have the same number of days.  The dashed lines are the 95% percentiles.  We see that there is an overabundance of quarter 1 boys, but look at the difference between July and August boys.  They are basically the same age, but July boys are much less frequent than you would expect and August boys are more frequent.   The strange birth month frequency for the U18's (birth year 1994) presumably shows the effect of college.  The boys born in 1994 in Jan-July would be in college while the 1994 Aug-Dec boys are high school seniors.