Most and least popular birthdays

In the English-speaking world, more people are born in September than any other month of the year; the least popular birthdays (outside of leap days) are around Christmas, New Year, and other public holidays.

When I was a teenager, I entered a science fair. I don’t remember my entry, but I remember another kid’s project very well. He had pulled birth data from public records and wanted to see if there was a birth spike nine months after unscheduled power cuts. It was a bold piece of research. Unfortunately, he messed up the statistics, so he never found out if there was a correlation or not. But the birth data does come with some amusing surprises.

In the English-speaking world, more people are born in September than any other month. This makes sense: it’s nine months from the start of the year, and (I guess) people make big decisions about their lives at the start of the year. That, or people like to celebrate Christmas and the New Year. You might think that those cold dark winter nights have something to do with it, but this pattern persists in the Southern Hemisphere as well.

The funny thing is that, in contrast, the least popular birthdays (not counting leaps days) fall on public holidays. In the UK, New Year, Christmas, and the days immediately around them are among the least popular. In the United States, those holidays plus the Fourth of July and Thanksgiving are the biggest gaps.

I have a theory about this. A significant proportion of births in these countries are not spontaneous but are medically-induced or surgical (c-section) births. (Apparently up to a third of births in the United States are by Caesarean.) Some of these non-spontaneous births are emergencies, of course, but many are scheduled and planned. And, as a general rule, hospitals don’t usually schedule surgeries for public holidays. Doctors and nurses need a break too! So, birthdays on public holidays are limited to non-scheduled births, and that drops the rate enough to make these the least popular days to be born.

(Speaking of birthdays, today this website is three years old. Thanks for reading!)

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