September 20

20 Sep 2022

As some may know, a strangely large number of Sacred Harp singers (including myself!) share a birthday of September 20 with the compiler of our tunebook, B.F. White. I was curious as to how large this effect really is, so I ran some numbers.

The 2020 Minutes Book, the last to publish a directory of singers’ birthdays, lists 9 singers with Sept. 20 birthdays. This is the most frequently occurring birthday, with the next most frequent being Nov. 30 with 7 singers. If we assume the directory is representative of the distribution of birthdays among all singers (in fact, I know of some that aren’t listed!), and since there were 765 singers in the directory, we can conclude that around 1.2% of singers share Major White’s birthday.

Using data published by the CDC’s National Center for Health Statistics for U.S. births for the years 1994 to 2003, we see that while September surely has the greatest share of high-frequency birthdays, Sept. 20 is only the 28th most popular, representing only 0.295% of the birthdays. Interestingly, Sept. 19 and Sept. 18 are the most popular with 0.306% and 0.305% respectively (the distribution is much flatter).

So, if we had a directory of 765 random birthdays from this broader population, we would expect to see two or three Sept. 20 birthdays (as opposed to the 9 we see in ours). In fact, when I ran one million simulations of random birthday directories the size seen in the Minutes Book, only 564 of the simulated directories had 9 or more Sept 20. birthdays. In other words, there was only a 0.0547% chance (1 in ~1828) of there being as many singers who share a birthday with B.F. White as we see in the Sacred Harp singing world he made possible.

Check out this notebook for calculations.