Expanding the size of police forces in mid- to large-sized U.S. cities leads to lowered homicide numbers as well as an increase in arrests for low-level crimes such as liquor violations or disorderly conduct, a University of Oregon-led study finds.

Researchers at four institutions examined the race-specific effects of such expansion, finding that in most cities a larger police force reduces homicide victimization for both Black and white Americans, with Black Americans experiencing the largest benefits in per capita terms.

However, in cities with the largest Black populations, police hiring disproportionately increased numbers of low-level arrests without providing equal public safety benefits.

“We find evidence that benefits of policing in terms of reduced homicides accrue for both Black and white civilians,” said Benjamin Hansen, the W.E. Miner Professor of Economics at the University of Oregon and research associate of the private, nonprofit and nonpartisan National Bureau of Economic Research.

“We see more reductions in homicide as more police are added,” he said. “However, the reductions are not nearly as large in the cities with the largest Black populations.”

Every 10 to 17 officers hired by urban police departments prevents one homicide, with larger impacts for Black Americans in the average city in the study. Arrests for other index crimes such as rape, robbery, burglary and aggravated assault also fell in cities that showed declines in homicide.

Investments in police manpower, however, were also linked to larger numbers of low-level arrests, or quality-of-life crimes that typically do not have victims and carry small misdemeanor penalties. The burden of these arrests fell on Black civilians at a rate 70 percent greater than among white civilians.

The findings, coming amid the national debate on defunding or reforming police departments, were based on federal data sources in 242 cities with populations greater than 50,000 for 1981-2018. The paper was released Dec. 14 as a National Bureau of Economic Research working paper.

Because the data indicate that Black Americans in cities with large Black population don’t share equally in public safety benefits, Hansen’s team concluded that Black communities are simultaneously over- and under-policed.

“Based upon the historical opportunity cost of police employment, our estimates suggest that ‘defunding’ the police could result in more deaths, especially in among Black Americans,” they wrote in their conclusion. “Of course, reducing funding for police could allow increased funding for other alternatives.”

In the study’s conclusions, the researchers also suggested policing alternatives, including place-based control strategies such as increasing trees and green spaces, restoring vacant lots, forming public-private partnerships and adding street lighting.

The authors also cited evidence for positive results achieved through social service strategies, cognitive behavioral therapy, mental health treatment, summer jobs for youth and community outreach efforts of local nonprofits.

A challenge, Hansen noted, is how to effectively implement such efforts at larger scales. Expanding successful pilot programs both within communities or in new locations, he said, offers unique challenges in maintaining program efficacy.

Ultimately, Hansen said, “It’s impossible to know what the effects will be of replacing investments in police manpower with investments in other forms of crime control or in urban renewal. This is simply not a strategy that has been tested by any major city in the modern era. Research can tell us about what is true in the past, but it can’t predict the future.”

Hansen’s three collaborators were Aaron Chalfin, a professor in the Department of Criminology at the University of Pennsylvania; Emily Weisburst, a professor of public policy at the Luskin School of Public Affairs at the University of California, Los Angeles; and Morgan Williams Jr., a postdoctoral fellow in New York University’s Robert F. Wagner Graduate School of Public Service.

—By Jim Barlow, University Communications