You’ve probably heard this fact before: children born in the winter tend to do worse than children born at other times of the year. A winter birth translates into lower earnings later in life, poorer health, and a whole host of other outcomes (It remains in my mind because I was born in February…).
There have been lots of theories put forward, most focused on environmental or institutional factors that may help to explain these differences. A common one is that children born in winter tend to be old relative to their classmates and this may affect outcomes, or we get exposed to better food at different times of the year, or women get out and exercise more during the summer, and so on.
Surprisingly (I say this after reading the paper) no one has really properly considered that it may be due to the fact that different women given birth to children at different times of the year. The birthdate has always been sort of assumed to be independent of background, but in retrospect it is not at all clear why this might be the case. Anyone who has been around a university would notice that there are a lots of big bellies as the semester ends.
A recent working paper by Kasey Buckles and Daniel Hungerman finds exactly this fact to be the case. People who give birth in the winter are more likely to have less education and to be of lower socio-economic status than women who give birth at other times of the year. The differences can actually be quite large – up to 10%.
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