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Extra babies on Valentine’s Day, fewer on Halloween?

Just in time for the holiday, X pointed me to an article by Becca Levy, Pil Chung, and Martin Slade reporting that, during a recent eleven-year period, more babies were born on Valentine’s Day and fewer on Halloween compared to neighboring days:

What I’d really like to see is a graph with all 366 days of the year. It would be easy enough to make. That way we could put the Valentine’s and Halloween data in the context of other possible patterns. While they’re at it, they could also graph births by day of the week and show Thanksgiving, Easter, and other holidays that don’t have fixed dates. It’s so frustrating when people only show part of the story.

The data are publicly available, so maybe someone could make those graphs? If the Valentine’s/Halloween data are worth publishing, I think more comprehensive graphs should be publishable as well. I’d post them here, that’s for sure.


  1. zbicyclist says:

    1. You’d also need to separate out scheduled c-sections. Scheduling on 2/14 seems like a plus, 10/31 a minus. No doctor’s going to want to schedule a c-section on Thanksgiving.

    2. as one of 5 children all born on exactly the due date predicted months before, I have always been a believer in maternal effects. Mom was going to let us stay in there full term, but no longer. (yes, my ancestry is German. Was that a lucky guess?)

    • Scott says:

      Interesting, but they don’t seem to have given much thought to alternative explanations. How accurate are the records ? – where I live you have six weeks to report a birth & I don’t suppose anyone would be checking much whether you’d adjusted the date a bit. What counts as induction ? – stretch & sweep is suppose to help & one can imagine midwives keen to get home to champagne, roses, &c. being a little more zealous with the examinations. It’s probably hard to tell from the data alone, but a look at more co-variates might give some clues.

  2. Jonathan says:

    This might be a morbid observation, but should we not just look at the number of births, but the number of births and deaths? I doubt this has any impact on the results. Anyone know of a database of mortality records of this sort?

  3. Keith says:

    Bill Evans and Tim Moore took a similar — and very intersting — look at deaths.

    Here’s a really interesting look into deaths:
    available here:

  4. Joshua Gans says:

    And fewer are born on Feb 29 and April 1.

    Joshua Gans and Andrew Leigh (2012) “Bargaining over Labor: Do Patients have any Power?” Economic Record, forthcoming.

  5. [...] 15, 2012 | Leave a Comment | Joshua Gans TweetAndrew Gelman points me to this new paper that examines birth rates on Valentines Day and Halloween. Given the [...]

  6. Jeremy Miles says:

    I’d also like to see (I suppose I could work out) the days of the week. More babies are born on weekdays, ‘cos you don’t schedule a c-section or an induction on a day that it might interfere with your golf game.

    (This is the reason for the power cut in New York leading to more births nine months later, according to Robert Abelson. A journalist was in a hospital, and asked if more babies were born that day than normal. Someone replied “Yes”. The journalist counted back 9 months, and realized that there was a power cut, which they presumed led to people seeking old fashioned entertainment. The person in the hospital should have said “Yes, it’s Monday. There are always more babies born on Monday than usual.”

    • Andrew says:


      I wrote that in my blog post (specifically, “they could also graph births by day of the week”). The researchers definitely had these data; they say they controlled for day of week. I’d just like to see the data.

  7. That’s a fun fact for these holidays. On a related note, I wonder how many babies are conceived on these (and other) days. Would be interesting to do a time lagged posterior estimate of date conceived given our knowledge of typical gestational period, no?

  8. Rick Wicklin says:

    Here is a graph of US births in 2002 by each day of the year:

    The data show a strong “holiday effect.” An analysis of the holiday effect, with reference to sceduled C-sections, is available at

  9. demographer says:

    question from another culture:
    are the days 9 months before halloween and valentine special, regularly special?