• Authors: Jonathan Mummolo (Princeton University), Bocar Ba (Duke University), Haosen Ge (University of Pennsylvania), Jacob Kaplan (Princeton University), Dean Knox (University of Pennsylvania), Mayya Komisarchik (University of Rochester), Gregory Lanzalotto (University of Pennsylvania), Rei Mariman (University of Pennsylvania), Roman Rivera (University of California, Berkeley), Michelle Torres (University of California, Los Angeles)
• Title: Political diversity in U.S. police agencies
• Journal: American Journal of Political Science

From Black Lives Matter to Back the Blue, law enforcement has emerged as a hotly debated partisan issue over the last several years. But up to now, little has been known about the politics of the law enforcers themselves. How do police officers’ political affiliations compare to those of the people in their jurisdictions? Do officers of different parties enforce the law differently?

To find out, a team of researchers led by Jonathan Mummolo, an associate professor of politics and public affairs at the Princeton School of Public and International Affairs, proceeded along two lines.

First, they obtained rosters of police officers from 99 of the top 100 largest local police agencies in the United States – approximately 220,000 officers who comprise more than a third of local law enforcement officers nationwide – and matched them to a national voter file containing demographic information on registered voters, including estimates of their likely partisan affiliation. Second, they conducted a behavioral analysis on two large police departments, in Chicago and Houston.

“This is the most comprehensive examination of descriptive representation in policing to date,” Mummolo notes. “The ability to compare officers to their local jurisdictions on a large scale required extensive original data collection. Most studies in this area focus on a single jurisdiction, or use national surveys of officers scattered across the U.S., preventing local comparisons. We hope the approach to data collection we demonstrate in this study can provide a useful guide to expand the scope of studies in this literature.”

After comparing officer partisanship, as well as a host of other traits including voter turnout, race, sex, and household income, to the average traits of civilians in their jurisdictions, the team found that, on average, the police “diverge from civilians on every trait we can measure,” according to Mummolo. “They are more likely to be Republican, white, male, have higher household incomes, and to turn out to vote.”

Despite the overall demographic differences between the police and the populations they serve, the researchers noted that in some cases, departments are highly representative of their civilians, at least in terms of party affiliation and race.

The study of the Chicago and Houston police forces revealed that regardless of their party affiliation, officers in similar circumstances generally behave alike, making similar numbers of stops and arrests and using force at similar rates. However, officers of different racial groups behave much differently. Black and Hispanic officers make fewer stops and arrests in Chicago, and Black officers use force less often in both cities. Comparing same-race partisans, they found that white Democrats make more violent-crime arrests than white Republicans in Chicago.

“Police agencies have made substantial strides toward diversifying their agencies in recent decades in terms of officer race, ethnicity, and gender,” Mummolo says. “Our data show that while there remain substantial gaps in descriptive representation on some dimensions, those gaps do not generally correspond to differential treatment of civilians on the ground.”

The variation in representativeness the data reveal across agencies suggests new lines of inquiry, according to Mummolo.

“This raises questions about whether and how recruitment efforts, self-selection, or other factors impact the makeup of U.S. police agencies and how that varies across places,” he says.

The researchers note that not all of the demographic differences correspond to differences in officer behavior. “Diversification has occurred, and we are able to see how it is playing out on the ground in terms of police-civilian interactions,” Mummolo says, adding that whether further diversification would yield new results is difficult to forecast.

“But our study provides a template for making careful comparisons between officer groups, which can be useful not only for questions related to diversity in hiring, but also for detecting ‘outlier’ officers whose behavior is out of step with peers,” he says.