Everyone who has read SuperFreakonomics knows that the month in which you are born can have an influence on your life. I don’t want to start talking about horoscopes (no, really), but it’s interesting to notice that you have an advantage in the NBA when you are born in the first months of the year. The influence of how schoolyears are organised can be (in part) an element of explanation. Other examples of the influence of season of birth are better health outcomes for Spanish men born in June or July or better health outcomes for German men born in the late fall and winter, maybe due to weather conditions  (references in the following research).

But what if there is something else involved in the equation?

This paper by Kasey S. Buckles and Daniel M. Hungerman and published in the The Review of Economics and Statistics looks at the influence of the background of the mothers on the season of birth.  Are children born at different times in the year conceived by women with different socioeconomic characteristics? They found there is:

“Women giving birth in winter are more likely to be teenagers and less likely to be married or to have a high school diploma. These effects are large in magnitude and are observable for children born throughout the second half of the twentieth century. We show that these seasonal changes can account for a large portion of the poorly understood relationship between season of birth and other outcomes.”

Do notice that for this study the researchers used American data, it sure is interesting to investigate this in other regions.

Abstract of the research that can be read for free:

Season of birth is associated with later outcomes; what drives this association remains unclear. We consider a new explanation: variation in maternal characteristics. We document large changes in maternal characteristics for births throughout the year; winter births are disproportionately realized by teenagers and the unmarried. Family background controls explain nearly half of season-of-birth’s relation to adult outcomes. Seasonality in maternal characteristics is driven by women trying to conceive; we find no seasonality among unwanted births. Prior seasonality-in-fertility research focuses on conditions at conception; here, expected conditions at birth drive variation in maternal characteristics, while conditions at conception are unimportant.