Amid the public outcry following the spate of high-profile fatal police shootings of black men, communities have called for police departments to diversify their ranks to better reflect the populations they serve.

From St. Paul, Minn., to Baton Rouge, Charlotte to Ferguson, Mo., activists, newspaper editorials and even the White House urged police departments to recruit more black and Hispanic officers to combat the police violence that disproportionately impacts communities of color.

But a new study finds that adding black police officers is not an effective strategy for reducing police shootings of black citizens in the vast majority of cities. In fact, hiring more black officers could lead to even more violent interactions with black citizens — at least until they make up more than 40 percent of the police force, according to researchers at Indiana University’s School of Public and Environmental Affairs.

“Police organizations that have higher percentages of black officers are likely to have more police-involved homicides of black citizens, until they reach a critical mass,” said Sean Nicholson-Crotty, an author of the study who teaches public affairs at Indiana University.

The paper — “Will More Black Cops Matter?” — is slated to publish in Public Administration Review next month.

Explaining this counter-intuitive outcome may come down to a simple concept: the desire to be accepted as a member of a team. Black officers may feel they cannot advocate for the interest of black citizens in fear they might be “perceived as violating prevailing norms,” the authors wrote.

“African Americans in any organizations — if you were only one of a small handful of people working in a place who look like you — would be more likely to really toe the organizational line, but it’s even more so the case in police organizations,” Nicholson-Crotty said in an interview. “Police tend to have heavily socialized insular cultures. It’s sort of an us versus them mentality. They have a dangerous job and as a result, they really stick together and look out for and defend one another.”

He noted that the strongest predictor of how many black people police kill is how many white people are killed.

“Some police organizations simply use lethal force more than others,” Nicholson-Crotty said. “If the organizational culture is aggressive, you’d get stronger adherence” among minority officers.

That desire to belong plays out in the field with troubling consequences: Previous research has shown that black officers are more likely than their white colleagues to racially profile black drivers and disproportionately arrest black citizens. Some researchers have suggested that black officers may be tougher on black citizens because they are working to make black communities safer.

Other studies have resulted in contradictory findings. Some researchers found a correlation between an officer's race and the race of the person who is detained. Others have not.

Last month, a study published by the British Journal of Criminology revealed that white officers are more coercive toward black suspects, but black officers’ use of force is unaffected by the suspect’s race. There's been little research into the correlation between an officer’s race and the victim's race in police homicides.

Nicholson-Crotty and his colleagues analyzed police-involved homicides in America’s 100 largest cities, using data gathered by advocacy group Mapping Police Violence in 2014 and The Washington Post in 2015. Before those sources, comprehensive data on police homicides by race of the victim was unavailable, the researchers said. The Post has documented more than twice the number of fatal shootings recorded by the FBI annually on average.

As was the case in 2015, The Post found that a disproportionate number of those killed in police-related shootings in 2016 were black, whether or not the victims were armed. When adjusted by population, African American males were three times as likely to be killed by police as their white counterparts, The Post found. And 34 percent of the unarmed people killed this year were black males, although they make up just 6 percent of the population.

Only when black officers are represented in high enough numbers — more than 40 percent — are they likely to represent the interests of black citizens, the Indiana University study concluded. At that threshold of representation, they may no longer fear repercussions from their organizations or scorn from their peers. 

“There is an inflection point at which black officers may become less likely to discriminate against black citizens and more inclined to assume a minority advocacy role or to become neutral enforcers of the law,” the researchers wrote.

But in places like Ferguson, where African Americans make up only 11 percent of the police force and which has begun a minority recruiting program, even tripling black representation would not reach the critical threshold.

In 2016, The Post sought demographic information about every officer involved in an on-duty fatal shooting. So far, only a third of police departments that had officers involved in at least one fatal shooting last year have provided the officer’s race. But The Post has found, so far, that black and white people shot and killed by the police are more likely than not killed by an officer of their own race.

In the cases in which the officer’s race is available, about 60 percent of black officers involved in a fatal shooting in 2016 shot a black man or woman, while about 54 percent of white officers who shot and killed someone in 2016 shot a white man or woman.

For cities whose police departments approach the 40 percent threshold noted by the Indiana University researchers, adding black officers could help increase police legitimacy in the eyes of the communities they patrol without further jeopardizing the lives of black citizens, Nicholson-Crotty noted.

In most cities, however, reaching critical mass means black officers would be overrepresented in the police force compared to the cities’ overall black populations. There may be reasons to pursue such overrepresentation, he said. But reducing police homicides of black citizens should not be one of them.

“We are not arguing that increasing minority representation can’t do other good things, but if you had to get as high as 40 percent, it’s unrealistic as a solution for this particular and really significant policy problem,” he said, noting the widely documented challenges to recruiting and retaining minority officers.

Percent of black full-time sworn police officers (select cities)

Spokane, Wash. 1.9%

Sacramento 3.97%

St. Paul, Minn. 6.11%

Omaha 7.5%

Jersey City 10.01%

Nashville 12.3%

Tampa 14.47%

Houston 21.72%

Chicago 24.66%

St. Louis 32.68%

Memphis 50.35%

New Orleans 58.21%

Washington 59.3%

Source: 2013 Law Enforcement Management and Administrative Statistics, Bureau of Justice

Washington Post reporter Wesley Lowery contributed to this report.