Survival rates for Black women are far worse after bystander CPR than for White men, according to a study published this month in the American Heart Association journal Circulation.

The study highlights a troubling disparity in the effectiveness of bystander CPR for cardiac arrests that happen outside a hospital setting. While bystander CPR generally improves survival rates, its benefits are notably reduced for Black individuals and for women, according to the study.

The study looked at more than 623,000 patient records and found that nearly 40% of people who experienced cardiac arrest outside of a hospital received CPR from a bystander. A bystander is defined by the study as a non-professional responder like a family member or passerby. CPR can be performed simply by doing hard and fast chest compression, doubling or tripling a person’s chance of survival, according to the American Heart Association.

Dr. Paul Chan, a cardiologist at Saint Luke’s Mid America Heart institute in Kansas City and the lead author on the report, told CNN that the goal of the study isn’t to prove what is already known: Communities of color are less likely to receive CPR. Rather, the goal is to answer a two-fold question: Did CPR get started by a bystander, and does the patient have the same benefit, regardless of their sex or race or ethnicity?

“It’s not just getting people to start CPR but doing it as effectively and as well in all groups of people,” Chan told CNN.

The study reveals that on average, those who received bystander CPR had a 28% higher chance of survival compared with those who did not.

However, survival outcomes varied significantly by race and gender. White men who received bystander CPR were 41% more likely to survive than if they didn’t receive CPR, while Black women had the lowest rate, with only a 5% greater chance of survival, than if they didn’t receive CPR.

The study suggests “that variability in dispatcher training and resources could lead to lower-quality dispatcher instructions for CPR in Black communities.” The authors also note low CPR training rates in communities of color. Both of these factors could contribute to a disparity in survival rates.

However, the study notes that “future research is needed to determine the reasons why the association between bystander CPR and survival is weaker for Black individuals and women.”

Chan called the findings “alarming.”

“If we think of somebody with cancer, and let’s say there’s a very effective treatment for breast cancer or colon cancer. We worry about if there are differences in starting treatment for cancer, if women or Black individuals have a lower likelihood of receiving effective chemotherapy or treatment. But would we also be concerned if, when that treatment is started, the benefit is much less for certain groups of people?” he asked.

“What’s different about bystander CPR compared to a medication is that a medication can be standardized. You have a certain dose, let’s say, of chemotherapy – 50 milligrams – and everybody gets 50 milligrams. But with CPR, the quality and type of intervention may vary widely depending on who is performing it.”

Chan says that people might be uncomfortable performing CPR on a woman because manikins used in formal CPR training typically don’t have breasts.

Jade Calvin, a critical care paramedic at Bell Ambulance in Milwaukee, has been a dedicated emergency services professional for nearly eight years and now works in the Education Department as a CPR instructor, teaching new protocols.

“People are more hesitant to do CPR on women,” Calvin told CNN. “If you think of men, it’s more socially acceptable. It’s normalized for them to have their chest exposed, but not for women. So when they go to do CPR, people are scared because they want to keep the woman’s modesty intact.”

Calvin also noted that when CPR is performed on women, there is often fear about delivering effective compressions. “It’s always said that you’re supposed to push hard and fast,” she said. However, “society generally thinks that women are more dainty and fragile than men are, so they’re scared of doing more effective CPR.

“You are going to break ribs. It’s OK,” Calvin said. “You just push hard and fast. Someone will take over soon enough.”

Chan says it’s more difficult to understand the racial disparities in the benefits of bystander CPR.

“We looked at the benefit of bystander CPR when the victim collapsed in the Black and Hispanic community,” he said. “The only group that didn’t get a benefit was Black individuals, in Black and Hispanic communities.” Chan said the quality of CPR is not necessarily always worse in Black and Hispanic communities, “because we’re not seeing it when Hispanic and White individuals get bystander CPR in those communities.”

Chan says the American Heart Association and the American Red Cross have significantly intensified their efforts to boost CPR training in historically underserved communities. These communities are now the focus of increased outreach and education initiatives to address long standing disparities.

Reflecting on her experiences, Calvin noted that when she first started in EMS, she was often the only woman or the only person of color in the workplace. She stressed the importance of representation in training: “It’s important for people to see people that look like them doing these training sessions.”

Calvin is optimistic about the growing diversity in the field. “Little boys and girls are seeing people that look like them, saving lives, which is going to make them want to do the same thing.”