Women earn more than half of all PhDs in the U.S., but as a 2008 study found, they comprise only 45 percent of all tenure-track faculty, 31 percent of tenured staff, and 24 percent of all full professors.
Women in science and engineering are paid an average of $60,000 a year, which is $24,000 less than their male peers. This is because science is institutionally sexist. It's built on social structures designed to give men a leg up—or, depending on your perspective, structures designed to push women down.
When gender is the only variable, institutions are more likely to give male scientists a job offer—and they pay them better, too.
Women aren't equally represented in the peer review process, the vital system by which scientific studies are vetted before publication.
Even in science-related fields, such as nursing, where women are the majority, a 2015 study in the Journal for the American Medical Association revealed that men are still paid more—to the tune of around $5,148 a year. And yes, that's after controlling for differences in experience and education.
In general, male researchers are less likely to hire women in their labs.
As women enter professions that were once primarily male, the salaries of those jobs decline. Put another way, as more women take on "men's" work, the work is valued less and less.