Birthday stats: special features & deleted scenes

Here’s a few goodies related to my piece on DoubleXScience: Is there a season for births? What birthdays tell us about human evolution and modern medicine

First, how I got the idea: I saw the heatmap in a Reader’s Digest at the gym. Almost flipped past it, decided to take a look, and ended up staring at it for a whole mile. Wow, the patterns you can see in there!

When I got home, I downloaded some birthdate data from and played around with it in R, plus did some searches of the literature. (For the article, I decided to stick with the literature instead of my data, since the authors of those papers had better data sets and had spent more than a few hours analyzing them.)  Here’s a graphic I made that got cut:


See, there are plenty of babies born year-round. The seasonality trend is small, but (as all those citations showed) very persistent.  The heatmap looks more dramatic because it’s color-coded by rank (the most popular birthday is #1, the least is #366, and those are the numbers that Matt Stiles graphed). The absolute numbers, to take 2009 as an example, were 361,922 births in the USA in September and 316,641 in February. Or to put it another way, September averaged 12,000 births per day, while February was closer to 11,300.

I love when I get retweeted by science writers I admire. @BoraZ called the piece “escellent” which sounds like a compliment. @maggiekb1 linked it from BoingBoing, which marks the second time my work has been featured there. The first was a few years ago, when I created a knitting pattern for nautiloids. (I mean, for people to knit nautiloids. Not for nautiloids to knit. I expect the needles would slip out of their tentacles.)

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