How commonly shared is your birthday? (were you born on a holiday?)

It’s rare that I meet someone else with my birthday, July 4.

Thanks to a cool new graphic from Matt Stiles, a reporter and data journalist, I now know just how rare.

The graphic shows you the average number of births in the U.S. per day and the ranking of number of births that day compared to other days of the year. The data covers from 1994 through 2014.

When I found July 4 on the chart, I learned that my particular birthday is the 363rd most common day of the year to be born in the United States. 363rd out of 366.

Here are the top five rarest dates, in case you’re curious:
1. December 25
2. January 1
3. December 24
4. July 4
5. January 2

Notice anything these dates have in common? Let me show you.

1. December 25 (Christmas)
2. January 1 (New Year’s Day)
3. December 24 (Christmas Eve)
4. July 4 (Independence Day)
5. January 2 (day after New Year’s Day)

They’re all holidays or right around holidays. In fact, the next seven rarest birthdays – 6th through 13th – all fall on typical dates for Thanksgiving, with Halloween also making an appearance. The 14th rarest is April Fools Day, followed by December 23.

You might be wondering, “What’s up with that?! Why do people not have babies on holidays?”

Research indicates that this phenomenon is at least partially due to “retimed births” – that is, inductions or planned cesareans that are scheduled to avoid certain days. In particular, doctors and other medical providers are less likely to schedule inductions on days that they want to have off – such as holidays or days adjacent to holidays. And, if parents have a say in scheduling inductions, they may be less likely to schedule one for a day that a child would have to share with some other event.

In particular, this recent working paper (a version of which is forthcoming at the Journal of Labor Economics) looks at this phenomenon in California hospitals. Within that study’s sample, days of and immediately after holidays had 18% fewer births than other days. The authors found that hospitals that discourage retiming births had a smaller decrease in number of births on and around holidays. The authors also found that there was no significant difference in rates of cesarean births compared to vaginal births during this time, and that the health outcomes for babies were similar.

There are a myriad factors that contribute to the timing of a birth, and these can vary across patients, providers, hospitals, and more. Do you know what factors influenced which day you were born? How commonly shared was your birthday according to this graphic? Comment below to share!

Celebrating my tenth birthday, at the Liberty Bell

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