A new study puts numbers behind what many Black folks already know: seeing Black people killed by the police is truly traumatic.

The study, “Police Killings And Their Spillover Effects On The Mental Health Of Black Americans: A Population-Based, Quasi-Experimental Study,” was published via the online version of medical journal The Lancet yesterday (June 21).

The researchers wanted to determine the “spillover” effects on the mental health of people not directly connected to the hundreds of Black Americans who die at the hands of law enforcement officers each year. To do that, they culled 2013, 2014 and 2015 data from the U.S. Behavioral Risk Factor Surveillance System, which uses telephone surveys to assess the health of United States residents. They then examined the self-reported mental health data of Black people who were surveyed within three months of a day when a police officer killed an unarmed Black person in their state. That data was pulled from the Mapping Police Violence database.

Of the 103,710 Black people who responded, 49 percent of them were exposed to at least one police killing in their state. The researchers found that each death corresponded with an increase in poor mental health days for this group. This decrease in mental health was not observed in White respondents, and was only associated with unarmed Black victims.

“Having seen something so horrific and traumatic that happened to someone else, I’m reminded in a very painful and salient way that the deck might be stacked against me,” study co-author and assistant professor of medical ethics and health policy at the University of Pennsylvania Atheendar S. Venkataramani told The New York Times with regard to how Black people may react to the killings. “It’s really about all the kinds of insidious ways that structural racism can make people sick.”

Venkataramani told The Times that the study likely underestimates the extent of the shared trauma, noting that many of the deaths over the last few years have had impact far beyond the states where they occurred.

The researchers concluded that programs should be implemented to decrease police violence and to address the mental health effects in Black communities when officers kill Black residents.