Cha also created models tracking workers who leave professions. She found that "having children increases overworking women's odds of exiting male-dominated occupations by 52 percent, as compared to their nonmother counterparts." Full-time working mothers left their professions at a rate of 4.9 percent, but when you look at professions where they work 50 hours or more a week, that number jumps to 6.8 percent (though she noted that holding an advanced degree reduces the exit rate by 1.7 percent).

Meanwhile, "being a father has no effect on the mobility of overworking men."

Cha says: "When we compare the exit rate of full-time working mothers (4.9 percent) to that of their childless counterparts (4.5 percent), the differences are negligible. This suggests that motherhood status alone does not increase the exit rates; what drives women's exodus from male-dominated occupations are the joint effects of overwork and motherhood, which may reflect the 'greedy' as well as 'gendered' nature of family that demands disproportionately more hours from mothers.

It's not the particular findings that surprised me, but how consistently I can actually see this influence in every dimension of women's labor market outcomes."

She argues that although a lot of attention has been given to the idea that professional or managerial occupations require long hours, the real correlation between long working hours seems to more strongly associated with how many men are in the profession, not the nature of the work.

"Work hours tend to be shorter in many female-dominated professional occupations, such as school teachers, librarians, and therapists, as well as lower-level managers, and the penalty for deviating from the norm tends to be smaller," Cha writes.

She goes on to point out that even non-professional male-dominated occupations like construction often require mandatory overtime.

America's somewhat unique in this tendency toward what she calls "overwork culture." Sweden, Finland, Germany, the Netherlands, Denmark, and the United Kingdom all cap working hours at 48 hours a week. And Americans have gotten worse over time. In 1979, 21 percent of men and 5 percent of women worked more than 50 hours a week. In 2000, 27 percent of men and 11 percent of women worked that much.

Those numbers might be even worse today, since, as Cha says, "the definition of 'being at work' has intensified over the last few decades." Thanks to smartphones and at-home access to work emails, today's workforce might be even more tipped toward "overwork" than even those included in her data. Technology hasn't made the problem of overwork better. If anything, it's made it worse.

Cha blames gender biases about work that haven't evolved much in the last few decades. "When people are really expected to dive into the workplace and have a complete devotion to work, that was probably possible because there was someone else who can do other things for that person," Cha says. "This overwork norm is basically built upon those assumptions."