Study highlights population mental health impact of events widely perceived to be a symptom of structural racism.
Police killings of unarmed black Americans have adverse effects on the mental health of black American adults in the general population, according to a new population-based study. With police killings of unarmed black Americans widely perceived to be a symptom of structural racism, the findings highlight the role of structural racism as a driver of population health disparities, and support recent calls to treat police killings as a public health issue.
The study was led by the Perelman School of Medicine at the University of Pennsylvania and Boston University School of Public Health (USA), in collaboration with Harvard University, and is published in The Lancet.
Police kill more than 300 black Americans - at least a quarter of them unarmed - each year in the USA. Black Americans are nearly three times more likely than white Americans to be killed by police and nearly five times more likely to be killed by police while unarmed . Beyond the immediate consequences for victims and their families, the population-level impact has so far been unclear.
The quasi-experimental study combines data from the 2013-2015 US Behavioral Risk Factor Surveillance System (BRFSS), a nationally-representative, telephone-based survey of adults, with data on police killings from the Mapping Police Violence (MPV) database. By using statistical analysis, the authors estimate the "spillover" effect of police killings of unarmed black Americans on the mental health of other black Americans living in the general population.
A total of 103,710 black Americans took part in the BRFSS survey during the three-year study period and rated how many days in the past 30 days they felt their mental health (in terms of stress, depression and problems with emotion) was "not good." Half of the respondents were women, and half had been to university. 38,993 respondents (49% of the weighted sample) resided in a USA state where at least one police killing of an unarmed black American had occurred in the 90 days prior to the survey.
Each additional police killing of an unarmed black American in the 90 days before the survey was associated with an estimated 0.14 additional days of poor mental health among black Americans who lived in the same state. The greatest effects were seen 30-60 days after the police killing.
Black Americans are exposed to an average of four police killings in their state of residence each year. Extrapolating their findings to total population of 33 million black American adults, the authors estimate that police killings of unarmed black Americans could contribute 55 million excess poor mental health days per year among black American adults in the USA. These estimates suggest that the population mental health burden due to police killings is nearly as large as the population mental health burden associated with diabetes among black Americans.
"Our study demonstrates for the first time that police killings of unarmed black Americans can have corrosive effects on mental health in the black American community," says co-lead author Atheendar S. Venkataramani, a health economist and general internist at the University of Pennsylvania. "While the field has known for quite some time that personal experiences of racism can impact health, establishing a link between structural racism - and events that lead to vicarious experiences of racism - and health has proved to be more difficult." 
Adverse effects on mental health were limited to black Americans, and exposure to police killings of unarmed black Americans was not associated with any changes in self-reported mental health of white Americans. Exposure to police killings of armed black Americans was also not associated with changes in self-reported mental health among black or white Americans.
"The specificity of our findings is striking," says co-lead author Jacob Bor, a population health scientist at the Boston University School of Public Health. "Any occasion in which police resort to deadly force is a tragedy, but when police use deadly force against an unarmed black American, the tragedy carries with it the weight of historical injustices and current disparities in the use of state violence against black Americans. Many have interpreted these events as a signal that our society does not value black and white lives equally. Our findings show these events also harm the mental health of black Americans." 
The authors suggest that the mental health effects of police killings of unarmed black Americans might be conveyed through several different channels, including heightened perceptions of threat and vulnerability, lack of fairness, lower social status, lower beliefs about one's own worth, activation of prior traumas, and identification with the deceased.
The authors note several limitations that should prompt further research in the field. First, the BRFSS public-use dataset was limited to state-level identifiers, and there was no information on the extent to which respondents were directly aware of police killings nor whether respondents were aware of police killings in other states. If police killings affected the mental health of black Americans living in other states, then the study findings would be an underestimate of the true effect. Secondly, the measures used in the BRFSS are self-reported. Thirdly, the study does not focus on other ways in which the criminal justice system disproportionately targets black Americans, and it is likely that other forms of structural racism--such as segregation, mass incarceration, and serial forced displacement--also contribute to poor population mental health. Finally, the study did not include data on other vulnerable populations, such as Hispanics or Native Americans, nor did it consider the impact of police killings on the mental health of police officers themselves.
Senior author Alexander Tsai, a psychiatrist at the Massachusetts General Hospital and Harvard Medical School, says, "Therapists and first responders are all too familiar with the potentially devastating effects of vicarious trauma. By highlighting the effect of police killings on the wider community, our study provides evidence on a national scale that racism can be experienced vicariously. Interventions are needed to reduce the prevalence of these killings and to support the mental health of communities affected when they do occur. For example, in the wake of such killings, affected police departments could deploy greater resources to community problem oriented policing, give community stakeholders subpoena powers in investigating officer-involved shootings, and pursue disciplinary actions against involved officers with greater transparency." 
In a linked Comment, Dr Rhea W Boyd, Palo Alto Medical Foundation (USA) writes: "Racism lands, violently, on bodies - not as a function of race but as a function of how humans order society (racial hierarchy), assign power (racial supremacy), and distribute resources (racial inequity). Labelling the attributable mental health outcome a "spillover effect", the authors adjoin the taxonomy of terms such as "weathering" and "toxic stress" to articulate potential pathophysiological mechanisms for the built harm of racism. This intentional naming of racism is crucial to advancing an anti-racist praxis in medicine and public health... Despite (the) limitations, the findings (of the study) are urgent and instructive. (The authors') work to acknowledge and address the clinical impact of police killing black Americans sits within a broader clinical imperative to rigorously define and intervene in the relationship between structural racism and clinical outcomes. This evidence should ignite inquiry into the broader health impacts of police violence and advance the challenge to confront racial health inequities as products of racism."