It had been known for decades that kids who are born during the winter test relatively poorly, drop out of school more frequently, earn less as adults and have a shorter life expectancy than those born at other times.
But no one knew why.
There were several theories, of course. One held that since winter babies reach age 16 earlier in the school year, they can legally drop out a bit earlier in their education. Another postulated that vitamin D played a role, since winter babies got less sunshine early in life. A third suggested that the cause was higher pesticide concentrations in the surface water during spring and summer, when winter babies were conceived.
These theories might have some validity, but Notre Dame economists Kasey Buckles and Daniel Hungerman have come up with another, more compelling explanation: winter babies are more likely to come from socioeconomically less-privileged families.
To reach this conclusion, the economists examined CDC birth-certificate data for 13 consecutive years beginning in 1989. In every year, winter babies were more likely to be born to teenage or unwed mothers, or mothers that hadn’t completed high school themselves.
For example, 13.2% of January babies are born to teen mothers, whereas the number is 12% for May babies, a statistically significant difference that, along with other findings like it, is large enough to explain at least 50% of the differences in earnings, education and mortality (according to Buckles and Hungerman).
The economists can’t explain the surprising link between socioeconomic status and the time of the year when babies are born.
Perhaps it’s related to seasonal variations in employment, since married women tend to conceive when they are unemployed, they say. Or perhaps it is due to cooler springtime temperatures, since hot weather decreases fertility, but only for those who live in homes without air conditioning.
Then again…January is roughly 9 months after prom season!