Although it can be impossible to plan in advance for a medical emergency, research published in the Proceedings of the National Academy of Sciences suggests that patients—especially women—who receive care from a medical professional of the same gender have a significantly higher chance of survival.

Laura Huang, associate professor at Harvard Business School, Brad Greenwood of the University of Minnesota-Twin Cities, and Seth Carnahan of Washington University in St. Louis share a common research interest in examining bias and disadvantage. “I’ve looked at [gender bias] a lot in terms of entrepreneurship and who gets venture-capital financing,” Huang said. “I’ve also looked at it in terms of hiring and promotion decisions within organizations.” Given how pervasive gender bias is in the workforce, the researchers felt compelled to apply this lens to healthcare, a context in which they believed there should be absolutely no bias or discrimination. “If you are somebody who has a heart attack and you go to the ER, the doctor’s only job is to save your life. It shouldn’t matter who you are,” Huang said. “The only outcome is that either your life is saved or not saved. It’s not like work where there are questions like, ‘Oh is this person capable of working well on our team? Or, are they qualified for this promotion?’”

Huang’s research is far from the first to indicate that implicit bias plays a negative role in healthcare. A huge body of research spanning decades has found that, among other outcomes, racial and ethnic minorities experience significantly higher mortality rates from chronic illnesses for reasons other than access to care or early intervention. There is also growing evidence that socioeconomic background plays a critical role in premature mortality rates in cities like Boston.

Despite these indications, anyone who comes into the ER with a heart attack has an 11.9 percent baseline rate of not surviving. Although the findings show that gender concordance—whether a patient is being treated by a doctor of the same gender––matters for both men and women (if a patient is seen by a physician who is of the same gender, her or his probability of death is reduced by 5.4 percent relative to the baseline mortality rate the statistics paint a much more dire picture for women. Female patients who are treated by male physicians are 12 percent more likely to die of a heart attack than an average patient: their absolute chance of dying is 13.4 percent.

“That’s pretty significant, when you really think about it,” said Huang. “You have a 5.4 percent increased chance of living, relative to the baseline mortality rate, if you’re seen by a physician of your gender.” Another way to interpret the findings is that females who are treated by a male doctor see an increased absolute risk of dying by about 1.5 percent. “This means that one out of every 66 women is suffering because they saw a male physician,” she said.

The researchers were careful to control for as many variables as possible, including patients’ medical history and which schools attending physicians attended. Huang said that they were especially mindful of existing research that suggests women are less likely to seek medical care early on and are also generally less likely to report pain levels. “If the implication was purely that women are harder to treat, then we should find that women who come in to the hospital with heart attacks have a lower chance of survival across all doctors. If they’re waiting longer to be seen, and that’s driving a higher percentage chance of dying, then that should hold true regardless of their doctor’s gender—it didn’t.”

While the research doesn’t point to one overarching reason why gender concordance plays this role in cardiac-arrest survival rates, Huang said that one strong hypothesis involves communication norms. “Perhaps there’s something implicit that’s happening where male physicians are not picking up on something tacit,” she said. The researchers found that when male physicians develop a history of treating more women or when they have more female colleagues, the negative effects (the higher mortality rates for women) are mitigated. “Because the effect is attenuated when these doctors have more women around them, this suggests there’s something to do with a communication mechanism or attention to detail,” she said.

Ultimately, the researchers aim to draw more attention to the implications of gender bias. “We see [bias] happening in other contexts, and in the medical arena we’re seeing the workplace being mirrored. We seeing glass ceilings in workplaces and in entrepreneurship and here, this is a glass ceiling on life.”