At Twitter, 10 percent of tech roles are staffed by women

In computing, the stereotype of male superiority has proved more stubborn. “The number one thing holding women back is stereotypes,” Corbett said. “The stereotype is that girls and women are not as good at math and science as boys and men are.”

“There’s evidence that by first grade, most kids already associate math with boys,” she said. “This is just a belief most of us have. It’s a reflection more of our culture than anything individual.”

Those prejudices tend to make their way into the hiring process. Both male and female hiring managers often view women as less competent in math or tech.

Men are twice as likely as women to be hired for a job in mathematics when the only difference between candidates is gender, according to a study published in a recent issue of Proceedings of the National Academy of Sciences.

For women who do choose computing, and who wind up in technical jobs, companies need to make a “welcoming environment” for them, said Corbett. Part of that is setting up a process that deliberately encourages diversity in hiring and retention.

Some companies are trying. Google is devoting resources to workshops on unconscious bias. Recently, Judith Williams, Google’s diversity manager, called out company Chairman Eric Schmidt for behavior that seemed biased.

But experts argue that workshops aren’t enough. Rather, they say, diversity needs to be made a clear priority at companies. That happens when diversity moves out of workshops and becomes factored into the hiring managers’ bottom lines.