By now, we’ve all heard about the low numbers of American women in science, technology, engineering, and math (STEM). Some argue it’s a pipeline issue – that if we can interest more young girls in STEM subjects, the issue will resolve itself over time. But that’s not convincing. After all, the percentage of women in computer science has actually decreased since 1991.

Another theory is that women are choosing to forgo careers in STEM to attain better work-family balance—rather than being pushed out by bias. But evidence for that is also thin. Several new studies add to the growing body of evidence that documents the role of gender bias in driving women out of science careers. A 2012 randomized, double-blind study gave science faculty at research-intensive universities the application materials of a fictitious student randomly assigned a male or female name, and found that both male and female faculty rated the male applicant as significantly more competent and hirable than the woman with identical application materials. A 2014 study found that both men and women were twice as likely to hire a man for a job that required math.

My own new research, co-authored with Kathrine W. Phillips and Erika V. Hall, also indicates that bias, not pipeline issues or personal choices, pushes women out of science – and that bias plays out differently depending on a woman’s race or ethnicity.

We conducted in-depth interviews with 60 female scientists and surveyed 557 female scientists, both with help from the Association for Women in Science. These studies provide an important picture of how gender bias plays out in everyday workplace interactions. My previous research has shown that there are four major patterns of bias women face at work. This new study emphasizes that women of color experience these to different degrees, and in different ways. Black women also face a fifth type of bias.

Pattern 1: Prove-it-Again. Two-thirds of the women interviewed, and two-thirds of the women surveyed, reported having to prove themselves over and over again – their successes discounted, their expertise questioned. “People just assume you’re not going to be able to cut it,” a statistician told us, in a typical comment. Black women were considerably more likely than other women to report having to deal with this type of bias; three-fourths of black women did. (And few Asian-American women felt that the stereotype of Asian-Americans as good at science helped them; that stereotype may well chiefly benefit Asian-American men.)

Experimental social psychologists have documented this type of bias over and over again in college labs, but this is the first time someone has taken that experimental literature and asked women whether it describes their experience in actual workplaces. It does.

Pattern 2: The Tightrope. Women need to behave in masculine ways in order to be seen as competent—but women are expected to be feminine. So women find themselves walking a tightrope between being seen as too feminine to be competent, and too masculine to be likable. More than a third (34.1%) of scientists surveyed reported feeling pressure to play a traditionally feminine role, with Asian Americans (40.9%) more likely than other groups of women to report this. About half of the scientists we surveyed (53.0%) reported backlash for displaying stereotypically “masculine” behaviors like speaking their minds directly or being decisive.

“I’ve gotten remarks like, ‘I didn’t expect someone Indian…and female to be like this,” said a micro-biologist. An astrophysicist told us she’d had to “damp down” her ambition and “become as amiable as possible,” going as far as to hide prizes and media attention. On the other hand, if women are assertive, direct, outspoken, or competitive, they may face dislike or even ostracism. “I’m pretty aggressive,” said a Latina bioengineer. “I find that both men and women…are going to immediately call [you a] witch. I’d use another word but it would be rude.”

Black and Latina women are particularly at risk for being seen as angry when they fail to conform to these restrictive norms. A biologist noted that she tends to speak her mind very directly, as do her male colleagues. But after her department chair angrily told her, “don’t talk to me like that” she felt she had to “put cotton candy in my mouth.” She now does a lot of deferring, framing her requests as, “I can’t do this without your help.” She explains, “I had to put him in that masculine, ‘I’ll take care of it role’ and I had to take the feminine ‘I need you to help me, I need to be saved’ role.’” A cancer biologist reported that she refrained from getting too animated in lab meetings, lest she trigger the “angry black woman” stereotype.

Pattern 3: The Maternal Wall. When professional women have children, they often find themselves running into a wall: their commitment and competence are questioned, and opportunities start drying up. Nearly two-thirds of the scientists with children reported running into this form of bias, across all races and ethnic groups. Women felt they were competing with men who had stay-at-home wives, and that colleagues often assumed that they would lose their drive after they had children.

“I have to fight very hard to show that I am good scientist as well as good mother,” said an Asian-American immunologist.

“There is an assumption,” noted a black microbiologist, “that your career is more of a hobby than a career, and you’re only going to do it until you find a husband and/or have a family.”

Pattern 4: Tug-of-War. Studies show that women who have encountered discrimination early in their careers often distance themselves from other women. An Asian-American statistician described how an older woman who “probably had to go through hell” made sure younger women did, too. This is just one of several ways gender bias can fuel conflict between different generations of women.

It’s not inevitable: about three-fourths of the women scientists surveyed reported that women in their work environments supported each other. And yet about a fifth of the scientists surveyed reported “I feel like I am competing with my female colleagues for the ‘woman’s spot’” – another common cause of conflict among women in organizations that are predominantly male.

Pattern 5: Isolation. Our new study uncovered a fifth pattern of bias that seems to apply mainly to black and Latina women. On our survey, 42% of black women agreed that “I feel that socially engaging with my colleagues may negatively affect perceptions of my competence,” only slightly more often than Latinas (38%), Asian-American women (37%), and white women (32%) – but in our interviews, black women mostly mentioned this pattern.

“A lot of times,” said a microbiologist, “There are things that people exclude me from because they say, ‘Oh, she’s going to be the only black person there… just don’t invite her, she won’t feel comfortable.’”

“You don’t know who you can trust,” said a biologist. “This has been a very lonely life.”

In some cases, the women intentionally kept their personal lives hidden in order to maintain their authority. One scientist said she avoided socializing with her colleagues because “to me, that lessens your authority.”

“I do not discuss personal things with people,” said another microbiologist. “Judge me for me, not my personal life.” She said she kept her personal life separate because “I don’t want anything in my family life to be used against me.”

A Latina geographer had a different take on social isolation, saying that white people are “afraid of people of color in a way, like just worried they’re going to say the wrong thing or do the wrong thing. So they avoid that entirely.”

These five major patterns of bias mainly function as implicit biases, reflecting stereotypes people may not realize they have. But we also found plenty of evidence that old-fashioned, explicit racial stereotypes are alive and well.

One black biologist recalled an advisor who turned to her and asked, “Hey, do you have any family on drugs or in jail?” Another remembered a comment a professor made about how she would know all about rats because she came from an urban area. “Everyone laughed,” she said, and no one understood why she was offended.

“I have actually heard people discuss Hispanic people as being lazy,” said a Latina in anatomy, in a stereotype that came up again and again in our interviews. And Asian-American women reported that people frequently assumed they were foreigners. Said a physicist, “I’ve had a number of conversations where people ask me where am I from. And the answer, ‘I’m from Pittsburgh,’ is really not what they want.” She’s often told she speaks English “surprisingly well.” Given that she was born, raised, and educated in the U.S., “I should speak English surprisingly well,” she said dryly.

And notably, nearly half of black women (48%) and Latinas (47%) report having been mistaken for administrative or custodial staff, an experience far less common for white (32%) and Asian-American (23%) women scientists.

It’s so tempting to attribute the paucity of women in STEM to pipeline problems or personal choices. But it’s time to listen to women scientists: they think the issue’s gender bias, and an increasing amount of research supports that view.

If organizations are truly interested in retaining and advancing women, they will approach the issue of gender bias the same way they do other business issues: develop objective metrics and hold themselves to meeting them.