Stress induces spontaneous abortions that affect male fetuses more than female fetuses. The April 1992 Los Angeles riots constituted six days of civil unrest. This study showed that male births in California State dipped following this event.

This paper highlights a temporal relationship between Cuban migration and male to female live birth ratio (M/F), with M/F dipping in response to the possibility of leaving Cuba, often followed by sharp rises associated with a predominantly male efflux from the country.