Make no mistake, the gender wage gap is real.

For every $1 a man earns, a woman working full-time in the same field tends to earn just $0.79.

But as Sarah Kliff recently explained for Vox, that statistic represents a symptom of a much larger problem inherent in the way Americans do their jobs.

Based on the best available data, the fields where the wage gap is largest have one thing in common: They do not offer flexible work hours.

If employers want to ensure they’re doing everything possible to pay people fairly, they should therefore create some wiggle room as far as when people can do their work.

One of the most compelling studies that Kliff cites in arguing for flexible hours comes from Claudia Goldin, an economist at Harvard.

By Goldin’s measure, the fields that offer the least flexibility — law, business, finance, and some health professions — have the biggest gender wage gaps. Those with more flexibility, such as pharmacy and science work, have smaller gaps.

These inequalities grow as people move deeper into their careers. Most college graduates, male or female, earn about the same amount in a given industry when they start out, Goldin explained on the Freakonomics podcast.

“Further down the pike in their lives, by 10-15 years out, we see very large differences in their pay,” she says.

Goldin explains that this gap arises because women have a stronger preference than men for “temporal flexibility” — the ability to work at odd hours so they can tend to children, family emergencies, and the like. But because of how many industries are structured, those flexible roles often tend to pay lower wages. Men, on the other hand, tend to value income growth and take on the caretaker role less often, so they don’t seek flexible hours in their jobs as much.

Goldin offers the example of a female lawyer who doesn’t necessarily want to work 80 hours per week at a big firm because she has priorities outside of the office. A male lawyer might be more willing to put in the hours required to make partner, whereas the female lawyer is more likely to seek a role that allows her to do some work from home, even though it pays less. Both work in the same field, but the man’s salary will likely be higher.

If companies want to help close the gender wage gap, they could try to treat their employees more like scientists and less like businesspeople, focusing less on when people punch in. Of course, it’s not always feasible to offer total flexibility, particularly for doctors who own their own practice or consultants who travel for work.

But for industries in which one employee can “sub in” for another, thereby giving the other more flexibility, fair pay is very possible. Providing that wiggle room won’t be a cure-all, but it could go a long way toward creating happier, more fairly treated employees.

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