Anecdotally, women have shared horror stories for years about their experiences with doctors—often male doctors. In addition to being dismissed and their pain not being taken seriously, some have reported being misdiagnosed as a result of gender bias.

Now, researchers have quantified just how dangerous this issue can be. In a paper published in the Proceedings of the National Academy of Sciences over the summer, researchers found that women are less likely to survive a heart attack when they’re treated by a male physician.

For the paper, researchers Laura Huang of Harvard Business School, Brad Greenwood of the University of Minnesota-Twin Cities, and Seth Carnahan of Washington University in St. Louis studied more than 500,000 heart attack patient cases in Florida hospitals from 1991 to 2010.

Huang had previously studied racial and gender bias in entrepreneurship and in workplace hiring. But health care, she says, is one setting where there should absolutely not be any disparities. “An emergency doctor comes in and is tasked with saving someone’s life,” she says. “Presumably, that doctor should be trying to save [a patient’s] life regardless of [the patient’s] gender.”

What Huang and her co-authors found was staggering: Female patients treated by male physicians were less likely to survive compared to all patients treated by female physicians or male patients treated by male doctors.

In fact, the gender disparity in survival rate was triple for women who saw a male doctor compared with those who saw a female doctor. “We were really struck by the fact that there’s actually a big difference in who survives something like a heart attack,” Huang says.

This paper does not look into health-care outcomes for women based on race, but previous research shows that women of color are likely to be disproportionately affected when it comes to medical care. Racism and racial discrimination against Black people, for example, increases their risk for disease and death. Segregation also increases Black women’s risk of pregnancy-related injuries.

And while the paper only looks at bias through the lens of the gender binary, other data suggests that patients who identify as nonbinary also deal with issues that can put them at risk and change health-care outcomes. Past research has shown that LGBTQ and gender-nonconforming people have postponed seeking medical care, and that people who told their doctors about their gender were largely dismissed or ignored. Class, disability, weight, and other factors that may affect treatment are also not addressed.

Still, this paper highlights the very real implications of gender bias for a majority of the U.S. population in health care. For some women, it magnifies the choice to seek out female doctors. Such is the case with Annalise Mabe, a 27-year-old from Tampa, Florida.

Last year, Mabe went to a male OB-GYN to check on a health issue. After disclosing her symptoms and past history, “he was really judgmental and said things like, ‘You are wild and crazy, huh?’”

Mabe says the doctor made jokes and assumptions about her sleeping around, despite the fact that she had actually been through a sexual assault, and he discounted her input. When she told him she had already had a full annual exam, for example, he said, “No, you didn’t” and proceeded to give her one.

“I didn’t realize that I should have said no or should have stopped,” Mabe says. “With the male OB-GYN, there was no communication when his hands were going to touch me. With a female doctor, they are very clear and communicative about the whole process.”

Mabe says this has been a common problem when she’s gone to see male doctors, some of whom have been condescending and dismissive. “If I bring up research, they assume I looked it up on WebMD,” she says.

Since the research came out, Huang says “so many people have reached to us and said, ‘Yeah, this has been my experience.’”

Now, Mabe seeks out only women doctors whenever possible in order to avoid similar situations. However, this won’t apply to people who are in circumstances where they cannot choose their doctor, whether because they are at an emergency room, in a location that has limited options for providers, or because of limitations due to their insurance plan.

One thing the paper seems to confirm is that patients, regardless of gender, fare better under the care of women physicians. This is just the latest research to make this suggestion. In 2016, researchers came to the same conclusion after studying the impact of a doctor’s gender on elderly hospitalized patients. Women doctors are also typically better at empathy and make better surgeons.

But for Huang, it’s not as simple as saying women are better at treating patients than men. To be sure, individuals can deviate from general patterns in either direction.

Their research does suggest that exposure to women colleagues makes male doctors better equipped at treating women patients. They found that when male physicians work in hospitals where they have more female colleagues and/or when male physicians have more experience treating female patients, those male physicians are better at treating female patients and the gender disparity in survival rates drops.

One reason for this, Huang adds, is that doctors may be trained in a way that’s framed toward the male experience—which could explain the issues Mabe and other women have had with male doctors.

Huang hopes to continue researching bias in health care outcomes by looking beyond gender. “Race, ethnicity, sexual orientation, class … all of these things that lead to bias are important to study in this setting,” she says.