Are birthdays really important?

A recent article by the Irish Examiner posited that it was better for a prospective Ireland international footballer to be born in the first three quarters in the year if he was born in Ireland, due to the summer soccer season here, whereas if the player were born in the UK, then they have a better chance of playing at the highest level if they were born outside of June, July and August, with the players born in September, October and November most likely to earn international caps.

However, the focus was only on one squad, the final squad of 2017 in the play off against Denmark, a tiny sample group considering the Irish national side has played more than 500 games, with over 300 players capped.

As well as that, it ignores that summer soccer only started in Ireland in 2003, and not all of the players marked as "Irish reared" came through in this system.

A minor gripe was that players who didn't appear in the play offs were included in the final table, however omitting them to only use players who received caps in the two games would have reduced the sample size even further.

With that in mind, we've compiled the following table using the same criteria, but increased the sample size to include all players who have been capped by Martin O'Neill since taking over in 2013.

Q1	Q2	Q3	Q4
Ireland: Jan-March	Ireland: April-June	Ireland: July-Sept	Ireland: Oct-Dec
UK: Sept-Nov	UK: Dec-Feb	UK: March-May	UK: June-Aug
16(31.3%)	11(21.5%)	17(33.3%)	7(13.7%)
Shane Duffy(January 1) Paul McShane(January 6) Glenn Whelan(January 13) Robbie Brady(January 14) Shane Long(January 22) Jeff Hendrick(January 31) Conor Hourihane(February 2) Andy Boyle(March 7) Daryl Murphy(March 15) Jonathan Walters*(September 20) Ciaran Clarke*(September 26) Cyrus Christie*(September 30) Keiren Westwood*(October 23) Alex Pearce*(November 9) James McCarthy*(November 12) David McGoldrick*(November 29)	Stephen Quinn(April 4) Alan Browne(April 15) James McClean(April 22) John O'Shea(April 30) Sean Maguire(May 1) Darren Randolph(May 12) Wes Hoolahan(May 20) David Meyler(May 29) Shay Given(June 20) Harry Arter*(December 28) Sean St Ledger*(December 28)	Aidan McGeady*(April 4) Paul Green*(April 10) Callum O'Dowda*(April 23) Robert Elliot*(April 30) Robbie Keane(July 8) Jonathan Hayes(July 9) Eunan O'Kane(July 10) Damien Delaney(July 20) Anthony Stokes(July 25) Andy Reid(July 29) Stephen Gleeson(August 3) Daryl Horgan(August 10) Marc Wilson(August 17) Kevin Long(August 18) Stephen Ward(August 20) Stephen Kelly(September 6) Kevin Doyle(September 18)	Anthony Pilkington*(June 6) Richard Keogh*(August 11) Seamus Coleman(October 11) John Egan(October 20) Darron Gibson(October 25) Alan Judge(November 11) David Forde(December 20)

As you can see, there is a marked difference with the table produced by the Examiner. Players born in Q1 and Q2 drop by 17 and 9 percentage points respectively, with those born in Q3 and Q4 increasing in 11 and 13 percentage points, respectively.

The real question is - what does all of this prove? Not a lot really, other than (as pointed out in the original article) you're less likely to get capped if you were born in the final quarter of the year in Ireland, or the summer months in the UK. 

It's hard to extrapolate anything from the small sample size of one squad, and even the larger size of 46 games under Martin O'Neill has the conclusion of a slightly better chance of playing international football if you were born in Ireland in the first three months of the year, or during late summer, or Spring or early Autumn in the UK

Maybe it needs further study?

Further reading
Why birthdays are one of the big problems affecting Irish soccer