The community gathers at George Floyd Square after Chauvin is convicted of murder.

Has the BLM Movement Influenced Police Use of Lethal Force?

The 2020 murder of George Floyd by former Minneapolis Police Department Officer Derek Chauvin triggered massive protests across the nation and around the world, increasing calls for police reform, transparency, and prosecutions. The protests — and the ongoing national conversation around race, inequality, violence, and policing — were largely created or inspired by Black Lives Matter.

The protest movement and its goals have been embraced by researchers and academics across disciplines. Yet to date, only a small number of studies have attempted to answer key questions about BLM and its impact, including whether police use of lethal force has declined since the movement began. Social scientists point to a central challenge: incomplete federal and state data on lethal force.

In the absence of such official data, social scientists are using various statistical methods and non-government datasets. Ultimately, however, police violence is a public health issue, researchers say, and public health agencies should take the lead on data collection. “If you’re not tracking the data,” says Glenn Ellis, a visiting scholar at Tuskegee University’s National Center for Bioethics in Research and Health Care and a bioethics research fellow at Harvard Medical School, “it’s impossible to understand the magnitude and know where to direct resources.”

CONVICTIONS: Where science & criminal justice meet.

“Black Lives Matter” began as a Facebook and Twitter hashtag in 2013, after the acquittal of George Zimmerman in the fatal shooting of the unarmed African American teenager Trayvon Martin. The political and social movement began in earnest the next year, after the fatal police shootings of Michael Brown and Eric Garner, who were also African American and unarmed. BLM reached its apex in the summer of 2020, when more than 20 million people are thought to have participated in nationwide protests after George Floyd’s murder.

For decades, researchers have studied social movements such as the Civil Rights Movement of the 1950s and 1960s, and the more recent #MeToo. Drawing on data from a wide variety of sources, researchers have been able to estimate the influence of individual social movements on the broader culture. Yet almost nine years after the start of Black Lives Matter, there has been “shockingly little” quantitative academic research on its impact, Travis Campbell tells me. Campbell will join Southern Oregon University’s economics faculty this fall. Campbell’s research on BLM’s impact on police use of lethal force was the subject of his recently defended dissertation at the University of Massachusetts Amherst.

Lack of comprehensive data is a key barrier. According to a recent paper published in The Lancet, one federal database dramatically undercounts the number of people killed by official force. The Centers for Disease Control and Prevention’s National Vital Statistics System failed to capture about 17,000 killings over almost four decades, according to the study authors, who reached this conclusion by comparing the federal database with three open-source databases that compile data from confirmed news reports. “More than half of all the deaths due to police violence that we estimated in the USA from 1980 to 2018 were underreported,” the Lancet authors wrote.

“There have been some efforts at the state legislative level to collect better data on use of force,” Justin Feldman, an epidemiologist at the Harvard T.H. Chan School of Public Health, tells me. “But for whatever reason this has largely gone under the radar of academia and policy.”

Last fall, Feldman and Mary Bassett, who is now health commissioner for the state of New York, published a call to action for public health data collection around deaths in police custody. The researchers concluded that the lack of data collection is a failure of federal and state public health agencies. “Six years after a police officer killed Michael Brown in Ferguson, Missouri, the United States does not even have an official nationwide system that documents all deaths in police custody, much less one that provides detailed and timely data to the public,” the authors wrote.

“There are about 18,000 law enforcement agencies in the country. Only about 30 percent of those are reporting data to this database,” says Henderson.

While the Department of Justice administers two databases to collect data on lethal use of force, the authors wrote, these databases rely on voluntary reporting and counted fewer than half of deaths in police custody.

“There are about 18,000 law enforcement agencies in the country. Only about 30 percent of those are reporting data to this database. We don’t know what the other 70 percent are doing,” says Howard Henderson, a criminologist based at Texas Southern University, a historically Black university in Houston. Henderson was not involved in Feldman’s research.

Feldman and Bassett’s paper offered three recommendations: improve data collection and reporting through public health agencies, establish review committees for deaths in police custody, and reform death investigations.

The last suggestion is particularly important, researchers say. The Minneapolis Police Department’s early press releases blamed George Floyd’s death on heart issues and substance abuse. The very first press release on Floyd’s “‘medical incident’” neglected any mention of “officers restraining him on the ground, a knee on his neck, or any sense of how long this ‘interaction’ lasted,” CNN reported.

Chauvin was eventually convicted of murder and manslaughter. The three additional former Minneapolis officers who arrived on the scene were convicted of federal civil rights violations in February 2022 for failing to intervene and depriving Floyd of medical attention.

In 2018, a trio of researchers published what was likely among the first quantitative research papers on Black Lives Matter. In the year following the killing of Michael Brown, protests were more likely to occur in communities that had experienced a death in police custody, the researchers found. The authors — Vanessa Williamson of the Brookings Institution; Kris-Stella Trump, then of the Social Science Research Council and now at the University of Memphis; and Katherine Levine Einstein of Boston University — determined that BLM demonstrations happened in 60 percent of all cities that experienced at least one such killing by police officers of an unarmed Black person. They noted, however, that their research relied on open-source databases, which “may be incomplete.”

A more recent paper, published in 2021, analyzed whether racial disparities in police-caused deaths have fallen in the years since the beginning of the Black Lives Matter movement. The researchers, based at the University of Pennsylvania, Yale University, and Drexel University, respectively, used The Washington Post’s award-winning Fatal Force database of fatal police shootings. Prior to the study, Post reporters had found that roughly 1,000 fatal police shootings occur each year. About half the people fatally shot by police officers each year are White, The Post reported, but African American, Hispanic, and Native Americans are shot and killed by officers at disproportionally higher rates. Black Americans, for example, comprise only 12 percent of the population but are twice as likely to be killed as White people.

The research team reviewed the Post’s database for 2015 to May 2020. During that period, 5,367 deaths were recorded, and of the cases where age and race were available, 51 percent of the victims were White, 27 percent were Black, 19 percent Latino, 2 percent Asian, and 1.5 percent Native American.

The researchers found “a small, but statistically significant decline in death rate for White victims” over the five-year period. They found no significant changes for the other groups. The data also showed that unarmed Black and Latino victims were killed at higher rates than unarmed White victims.

Elle Lett, an epidemiologist and MD candidate at the University of Pennsylvania’s Perelman School of Medicine, and the paper’s first author, noted that the trend held for Black, Hispanic, and Indigenous people “regardless of armed status.”

“It doesn’t matter if they were qualified to be an immediate threat to police officers,” the victims were still killed at higher rates than White people, Lett says on our call during an Amtrak ride from Boston to Philadelphia.

The paper is one of only a few to quantify years of life lost due to fatal shootings by police. In this case, the researchers found that each year, police shootings lead to about 32,000 years of lost life, with African Americans and Latinos disproportionately affected.

The study demonstrates that “Black people are killed by police at younger ages and more potential years of life are taken from them,” says Feldman, who was not involved in this paper.

“So, the racial inequalities are even larger than they appear on the surface,” he added.

Although the number of people killed nationwide by police officers has remained relatively stable since the beginning of the Black Lives Matter era, the movement may have had an impact at the local level.

Some local communities that experienced BLM protests have seen an overall 15 to 20 percent decrease in lethal police force in the five years following the 2014 Michael Brown protests in Missouri. That’s according to a 2021 study by Campbell, which has not yet been peer reviewed.

This translates to around 300 fewer deaths nationwide from 2014 to 2019, according to the data, which is believed to be the first research to demonstrate a connection between BLM protests and fewer cases of lethal force. The dissertation research — which focused on BLM’s impact on police use of lethal force — used the Fatal Encounters and Mapping Police Violence databases for his analysis. These were two of the three databases used in the previously mentioned Lancet study.

Ajenai Clemmons, an assistant professor of public policy at the University of Denver who researches community-based policing strategies, notes that police killings occur unevenly across the country. “A jurisdiction might go years without an officer-involved death. Other jurisdictions may have several,” she says. “So, it makes sense where they have several is where citizens are mobilizing. When you look nationally at those numbers it may look steady, but if you look localized you may see these declines” in places where people protested.

Clemmons, who was not involved in any of the previously mentioned studies, adds that research findings also reflect the particular dataset chosen by researchers. The Washington Post database, for example, is limited to shootings while one of the databases that Campbell used, Fatal Encounters, is “far more inclusive,” tracking all fatal encounters, “from shootings to tranquilizers to high-speed chases that end in death,” Clemmons tells me.

Campbell used a difference-in-difference statistical model to compare census tracts that experienced at least one protest with census tracts that experienced no protests.

“The payoff for protesting is substantial,” the paper found. “Every five of the 1,654 protests in the sample correspond with approximately one less person killed by the police over the following years.”

One of the more intriguing findings in Campbell’s research was that census tracts with the largest and most frequent protests experienced the greatest declines in lethal use of police force. For every 4,000 participants in a local protest, the police killed one less person, according to the model.

Henderson, the criminologist, appreciates Campbell’s difference-in-difference analysis because it identifies some of the mechanisms around social protests, policing, and saving lives. “Campbell’s work is an opportunity to prescribe empirical analysis to movements that are dynamic, which I think is the brilliance of the work,” he tells me.

Campbell suspects that some of the decline can be attributed to greater use of body cameras among officers who work in areas with local protests. In the three years following the 2014 Ferguson protests, he says, the share of law enforcement agencies using body cameras doubled. “This is important, in my opinion, because one of the few policies that seems to have bipartisan support is body cameras,” Campbell tells me.

Campbell’s data on body-worn cameras mirrors trends reported by other researchers. The University of Chicago Crime Lab, for example, found the use of force by police dropped by almost 10 percent and complaints against officers decreased by about 17 percent after police departments switched to body cameras.

The three former Minneapolis Police Department Officers convicted of depriving George Floyd of his federal civil rights — J. Alexander Kueng, Thomas Lane, and Tou Thao — could face up to life in prison, according to The Department of Justice.

The three men will stand trial in June on state charges of aiding and abetting murder and manslaughter. The federal sentencing negotiations and state trial are expected to take months. As the cases wind their way through the court system, the fact remains that there are no federal or public health databases that will ensure that deaths like George Floyd’s — at the hands of police officers — are counted and known to the public.

Rod McCullom is a Chicago-based science journalist and senior contributor to Undark whose work has been published by Scientific American, Nature, The Atlantic, and MIT Technology Review, among other publications.