The same trends are true for dentists and physician assistants. (In other healthcare professions, such as pharmacy, the men continued to earn more -- but the wage gap had narrowed considerably.)
So what's causing it? The study's authors compared survey answers about income and other aspects of work from close to 6,300 doctors and 32,000 other healthcare workers. But the researchers weren't able to adjust for specialties, and so they speculated that could be causing at least some of the gap.
More men are surgeons, radiologists and other higher-paying specialists; women are more likely to become pediatricians and family care doctors, which are lower paid specialities. The study's authors weren't sure if women were entering the lower-paying fields out of a preference -- or because discrimination was making it hard for them to enter the higher-paying fields, like surgery. The researchers said it warranted further study.
But Catalyst, a respected non-profit advocacy group for female executives and professionals, has been tracking the issue for decades, and it notes that the gender wage gap is pervasive and common, even when you control for experience, hours worked, job level and education.
This chart, from their site, shows the gender pay gap across industries: