The annual health survey is done by telephone on a rolling basis throughout the year, and the researchers analyzed responses given by residents in states where a police killing had occurred in the three months before they were interviewed. They found that black Americans reported more “not good” mental health days in the period after a police killing of an unarmed black person, and that the killings accounted for up to 1.7 additional days of poor mental health a year.

The study’s authors could not say definitively that the respondents to the health survey knew about the police killings that had happened in their states, or describe how, precisely, the news about the killings might have harmed their mental health.

Still, Dr. Venkataramani said the effects were observable and real. If anything, he said, the findings might understate the extent of the trauma, as some police killings of unarmed African-Americans have become events of national significance, reaching far beyond the states where they occurred. (The study cited, among the most notable examples, the police killings of Oscar Grant III in California, in 2009; of Michael Brown Jr. in Missouri and Eric Garner in New York, in 2014; of Walter Scott in South Carolina and Freddie Gray in Maryland, in 2015; and of Stephon Clark in California, earlier this year.)

“Maybe this is the tip of the iceberg,” Dr. Venkataramani said.

While a study like this one helps to underscore the impact of police killings on black communities, what’s important is what is done with the findings, said Mama Ayanna Mashama, an activist and organizer in Oakland, Calif., who practices natural wellness healing. Ms. Mashama said she had seen firsthand how police violence can cause anger and angst, and damage the self-esteem of black Americans.

“We have to find ways of de-escalating police response to black people,” she said. “It has to become policy. It has to become part of how it’s implemented from the top down. We have to have trauma-informed practices everywhere: in the schools, in families, in workplaces.”