Most Probable Birth Month
In a previous post I showed that the data from www.baseball-reference.com support Malcolm Gladwell’s contention that more professional baseball players are born in August than any other month. Although this might be explained by the 31 July cutoff for admission to baseball leagues, it was suggested that it could also be linked to a larger proportion of babies being born in August.
In order to explore this idea I gathered data from http://www.cdc.gov/ for births in the USA between 1994 and 2014. These data as well as the baseball data have been published as a R package here. Install using
Let’s explore the hypothesis regarding non-uniform birth months.
There is definitely significant non-uniformity:
We can dig into that a little deeper and see the total number of births between 1994 and 2014 broken down by month. The aggregate for August is certainly higher than any other month, but only marginally larger than that for July.
Delving still deeper we find that the monthly counts exhibit significant variation from year to year and that August has some appreciable outliers.
Specifically, August in 2006 and 2007 appear to have been bumper births months. Interesting!
Of course, a peak in overall births in August does not mean that there’s a direct causative link to the peak in professional baseball players’ births. But the contribution cannot be ignored.