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Caregiving responsibilities for infants and small children "are concentrated at an important period in men's and women's career trajectories," the study's author, sociologist Sarah A. Burgard, observed in the June issue of the journal Social Forces. "If women take the night shift routinely during this period, inadequate sleep could endanger their productivity and opportunities at work." Thus "responsibility for the night shift may mark an important source of gender stratification" and "could contribute to inequality in more commonly studied domains, such as earnings or career advancement."
Burgard also noted that other research has indicated women have higher levels of depression and anxiety linked to poorer sleep quality.
Burgard extracted data from the American Time Use Survey, a large sample of time diaries collected from adults nationally between 2003 and 2007 by the U.S. Census Bureau. "Physical care" for a child was overwhelmingly the most common middle-of-the-night caregiving activity—it accounted for 83 percent of all reported sleep interruptions. The time use survey didn't define "physical care" precisely enough so that Burgard could discern how much of it was breastfeeding. But Burgard pointed out in the study that "the night shift extends far beyond the average duration of exclusive breastfeeding among American women" (estimated to be 19 weeks), and that significant sex disparities in sleep interruption exist among parents of older children as well.
Interventions aimed at improving sleep "generally target individual health behaviors, such as alcohol, tobacco or caffeine use" or suggest better sleep routines, Burgard wrote, "but do not take gendered social role responsibilities like parenthood into account."
Sheryl Sandberg, chief operating officer for Facebook, talks about the impact of those gendered social role responsibilities in the current New Yorker—she's profiled by Ken Auletta. "The No. 1 impediment to women succeeding in the workforce is now in the home," she says. "Most people assume that women are responsible for households and child care. Most couples operate that way—not all. That fundamental assumption holds women back."
Sandberg tells Auletta that in her previous job as a vice-president at Google she'd hired scores of executives, both male and female, but "the men were getting ahead. The men were banging down the door for new assignments, promotions, the next thing to do, the next thing that stretches them. And the women—not all, most—you talked them into it."
There are myriad reasons for this, of course. But what looks like less ambition sometimes may be plain weariness.