That result should not be too surprising. Several studies have shown that men outnumber women among the speakers of several scientific conferences. There’s even a site that collates examples of all-male panels.

Why does this happen? Hebl accounted for several of what she calls “yeah-but explanations,” which underplay these figures as the result of anything other than discriminatory biases. For example, some might argue that men outnumber women in many fields, and so any equitable selection process would naturally lead to more male speakers. But the team estimated the full pool of available speakers by counting every professor in their six chosen fields at each of the top 100 U.S. universities. And even after adjusting for the relative numbers of men and women in the various fields or ranks, they found that men are still 20 percent more likely to be invited to give colloquium talks than women.

Skeptics might also argue that the problem is a generational one: Science, for instance, has historically been skewed toward men, and when colloquia committees decide whom to invite, they’re prisoners of that history. But if that were true, and the arc of academia was slowly bending toward equality, then when assistant and associate professors—who are younger and more junior than full professors—are selected to give talks, the gender difference should be narrower. Hebl’s team found no such trend. “The people in whom we should see more parity aren’t showing us more parity,” she says.

“People sometime say: You know what? Maybe it’s the women,” says Hebl. “Maybe they don’t want to give talks, or they’re declining because they’re staying home with their kids.” That’s not what she found when she surveyed 186 professors who didn’t give colloquium talk at prestigious universities, but were in the same departments as those who did. Their answers clearly showed that women don’t decline colloquium invitations more than men, that they feel just as strongly that these talks are important for their careers, and that they’re no more likely to decline such talks because of family obligations.

“This dispels the widely held myth that women are less frequent speakers because they travel less,” says Jo Handelsman, from the University of Wisconsin at Madison. “Clearly, we need to test such assumptions before we absolve ourselves of culpability in creating biased slates.”

“Despite their presence in departments, women are not being asked to contribute to the intellectual development of their fields in the most coveted ways,” says Robin Nelson, from Santa Clara University, who has studied the prevalence of harassment in science. “This gendered discrimination minimizes women’s visible contributions to their fields, validating the idea that the greatest intellectual contributions are made by a few brilliant men.”