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Male Uber drivers get paid 7 percent more than their female counterparts in the U.S., according to a new study (pdf) by Uber, Stanford and University of Chicago economists.

That’s surprising, because Uber’s driver assignments and pay are gender-blind, meaning a driver’s gender isn’t considered when matching riders or assigning fares. Rather, pay has to do with trip length, distance and whether it’s happening during surge-price hours or not.

There are more male drivers — women make up 27 percent of Uber drivers in the U.S. — and male drivers tend to work longer hours. However, on an hourly rate, women still make less, according to the data, which measured trips by 1.8 million drivers from 2015 to 2017.

According to the study, discrimination on the customer side isn’t the reason for the pay gap, either.

So why are female Uber drivers paid less than men?

The study points to three reasons that make the gap disappear:

When and where: The times and places female Uber drivers work seem to be less profitable. That could be fewer overnight shifts, shifts with shorter wait times or surge-price shifts than men.

The times and places female Uber drivers work seem to be less profitable. That could be fewer overnight shifts, shifts with shorter wait times or surge-price shifts than men. Driver experience: Drivers who’ve been with Uber longer get paid more, on account of knowing which routes and times tend to pay more. In general, men work for Uber longer than women so they are more experienced. The attrition rate after six months is 77 percent for women and 65 percent for men.

Drivers who’ve been with Uber longer get paid more, on account of knowing which routes and times tend to pay more. In general, men work for Uber longer than women so they are more experienced. The attrition rate after six months is 77 percent for women and 65 percent for men. Speed: Male Uber drivers conduct more trips per hour than women, meaning they’re actually driving faster, according to the data. More trips mean more money. About 50 percent of the earnings gap is explained away by differences in driving speed.

The report comes out amid efforts by Uber to regain the trust of its drivers. The pay gap mimics gaps in much of the rest of the economy. A study last year by tech job platform Hired found that, on average, men in tech are offered 4 percent more for the same job at the same company. The gap is even more profound when race is considered.

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