Working the night shift can disrupt more than just sleeping patterns. New research by social demographer Harriet Presser at the University of Maryland shows that for married couples with children, working nights (between the hours of midnight and 8 a.m.) can greatly increase the risk of divorce or separation. The presence of children is essential: According to Presser's analysis of data from the National Survey of Families and Households, working nights does not lead to a higher risk of divorce for couples without kids. At the same time, she was surprised to find that working evenings - from 4 p.m. to midnight, a key period during which many child-caring activities occur at home - did not have a significant effect on marital instability for couples with kids. Says Presser: "As a society, we have finally moved away from the Ozzie and Harriet view of family life, but we haven't recognized how its needs have changed."