Why do women still make less than men? There may be a debate over the size of the wage gap between the genders, but there’s wide agreement that it exists. It’s not as bad as it used to be—the pay disparity narrowed sharply in the 1970s and 1980s—but since then the gap has stopped shrinking. Over the past decade it has remained stubbornly stable. Researchers, activists, and politicians have all tackled the issue, offering a range of explanations: overt discrimination; the fact that women work fewer hours so they can take care of the kids; a sort of self-segregation that leaves such less-lucrative fields as teaching and nursing female-dominated and higher-earning ones like finance and computer programming full of men.

A new paper in the American Sociological Review, flagged by the New Yorker’s Margaret Talbot, offers a fresh explanation: the crazy hours we work. “Overwork,” as the paper’s authors defined it, is putting in 50 or more hours a week. And a lot more workers, especially in high-earning professions, are overworking than they used to. Those workers are making more money than everyone else, not just because they work more, but because they make more per hour. As the paper’s authors, Youngjoo Cha and Kim Weeden, pointed out, hourly wages for all workers have remained relatively flat in recent decades, but the hourly wages of those who work those 50-plus-hour weeks have gone up.

Interestingly, Cha and Weeden found that overworking didn’t just used to be less common; it used to be less lucrative. As they point out, in 1979 overworkers’ hourly wages were actually lower than what they call “full-time workers”—those who worked 35 hours to 50 hours a week. By 2009, that had reversed, and over-workers earned six percent more per hour than full-time workers.

What hasn’t changed over that time, however, is that men are significantly more likely to be over-workers than women. “In 1979, 15 percent of men and 3 percent of women worked 50 hours or more per week,” Cha and Weeden wrote, “by the late 1990s, these percentages increased to 19 and 7 percent for men and women, respectively.” The gap has narrowed slightly in the last decade. “The overall story, however, is one of stability in the gender gap in overwork,” they concluded.

The authors offered a few potential explanations for the rising returns to overwork. If overwork has increased disproportionately in higher-paying professional and managerial jobs, that would increase average wages for it. The increasing popularity of so-called “tournament-style” compensation systems, in which workers are paid according to rank, and small differences in productivity can translate into large differences in pay, may also have played a role. And for the many jobs in which productivity is hard to measure, how much time one puts in at the office can be seen as a proxy for how much one gets done. (That’s a correlation that, speaking from personal experience, I can say is not always direct.)

Regardless of the causes, however, the overwork premium has the effect of especially disadvantaging those who—because they have responsibilities at home, as well as at work—are not able to put in those sorts of hours. Those workers in the U.S. today are still much more likely to be women than men.

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