More About Chess Players' Birthdays

Continuing with Chess Players Prefer to Be Born in February, which was based on FIDE rating data for 2002, I ran the same queries on the data for 2005. The list for the year 2005 had a little more than double the number of players -- and double the number of players with birthdays -- as the list for 2002. After determining that the same monthly patterns held in 2005 as in 2002, I checked a few other patterns.

In a comment to my previous post, SonofPearl wrote, 'being born at certain times of the year can mean that your competitive peers during childhood are younger than you, thus giving you an edge'. At first, I took this at face value, but when I started to think about it, I realized that I didn't understand what the statement meant.

The stats say that the average number of players born in a particular month declines during the year. This means there are more serious chess players born near the beginning of the year. It doesn't mean that they are more successful. Or does it?

The pool of FIDE rated players represents only a small fraction of the total number of people who like to play chess. FIDE rated players have taken chess more seriously and have been more successful at chess than non-FIDE rated players. To rephrase that first sentence, 'the average number of {Pick one: GOOD / SERIOUS / FIDE RATED} players born in a particular month declines during the year'.

With that in mind, how does the average FIDE rating of players born in each month compare to other months? Like this:-

With around 4000 players born in a typical month, the differences in average rating don't appear to be statistically significant.