James Knowles, the mayor of Ferguson, Missouri, wants to recruit more minorities to the city’s police force, where only three officers are black. With an initiative that includes a civilian review board and a scholarship program, Knowles hopes to increase the number of black officers and make the police force more reflective of the community (Ferguson is 60 percent black).

The mayor’s initiative comes after a series of clashes between police and residents and a grand jury’s refusal to indict a white police officer in the killing of an unarmed African-American youth, Michael Brown. It’s difficult to say whether more minority officers will help “calm tensions,” as Knowles put it, since the quantitative research regarding how individual officers interact with minority populations is equivocal. But the experience of police departments around the country suggests a diverse police force is better able to serve its community than a non-diverse one.

“When it comes to role models or empathy, it would certainly be extraordinarily valuable if the police force could reflect our communities,” Edward Flynn, the police chief in Milwaukee, Wisconsin, told me in September. As of 2010, the Milwaukee force was 68 percent white, even though just 38 percent of the city was. “We all want community acceptance. We all recognize that makes us more effective.”

That may be so, but many American police forces still struggle to look more like the communities they protect and serve. In hundreds of departments across the country, the percentage of whites on the force is over 30 percentage points higher than the percentage in their communities. Tensions between police and minority communities can create further barriers to recruitment from those communities. “Historically, [police work] has not been seen as a viable or honorable career choice for minorities,” said Clarence Few, a sergeant in the Savannah, Georgia police department.

Some departments appear better at recruiting and maintaining a diverse and representative police force than others, though, and it’s possible Ferguson could learn from their examples. For an earlier story with FiveThirtyEight’s Andrew Flowers, I collected data on police and community demographics for the country’s 75 largest departments and ranked them according to how well the demographics matched.

The cities at the top of this list, such as Jersey City and Newark, have an incredibly high overrepresentation of whites in their police departments. Some cities have better demographic matching between the city’s population and that of the police department, including Savannah, and very few departments have an overrepresentation of minorities.

Perhaps surprisingly, the city with the second-most representative police force was Los Angeles. LAPD’s diversity is a somewhat recent phenomenon, stemming from a series of Justice Department-mandated reforms that began in 2000 after a decade of scandals involving police brutality and corruption.

Under the auspices of Bill Bratton, now the commissioner of New York City’s police department, LAPD’s demographics changed radically, in large part because the force needed to compensate for a high attrition rate during the scandal-plagued years. According to a 2009 Kennedy School study, “in 1990, just over 30 percent of the graduates from the [police] Academy were Latino, 19 percent African American, 5 percent Asian or Filipino, and fully 45 percent Caucasian. Almost two decades later in 2008, 53 percent of graduates were Latino, 7 percent African American, 11 percent Asian/Filipino, and 29 percent Caucasian.”

Along with the demographic shift in the force came higher levels of approval from the people of Los Angeles, according to the same study: “We found the LAPD much changed from eight years ago, and even more so in the last four or five years. Public satisfaction is up, with 83 percent of residents saying the LAPD is doing a good or excellent job; the frequency of the use of serious force has fallen each year since 2004.”

“Today there is better transparency, they are more open to input than they were,” explained Peter Bibring, senior staff attorney for the ACLU of Southern California, which works with the LAPD on community partnership policing. “Is there more concern about community relationships? Yes,” Bibring said. But, he added, “Does that mean every division and every shift is in the community policing model? Absolutely not.”

Speaking on behalf of the LAPD, senior officer Bruce Borihanh said that establishing good relationships with leaders in minority communities and with organizations such as the ACLU and NAACP has helped with police recruitment and led to better relationships between minorities and the police overall.

To get minorities into its applicant pool, the LAPD sponsors test-taking events and gives workshops to help individuals prepare for and pass the recruitment test. The department also offers seminars throughout the city to help prepare recruits for interviews. Minority officers are encouraged to mine their communities for potential recruits. “Our officers are the best tools for recruitment,” Borihanh said.

In Savannah, the police department advocates for minority recruits internally throughout the application process, placing ads in minority publications and establishing relationships with historically black schools, said Few, the police sergeant. “We cannot rely on what comes through the door or minority populations will be underrepresented,” he said.

Recruiting minorities for police forces does improve minority communities’ relations with the police, but not for the reasons one might expect.

David Sklansky of Stanford Law School has shown that it’s difficult to draw a direct correlation between diversity and a reduction in police misconduct. While some studies show that in comparison to white officers, black officers get more cooperation from black citizens, are less prejudiced against African-Americans, know more about the black community, and are less likely to arrest black suspects, other studies show just the opposite. “There are studies finding that black officers shoot just as often as white officers,” Sklansky wrote in a 2006 article, “that black officers arrest just as often as white officers; that black officers are often prejudiced against black citizens; that black officers get less cooperation than white officers from black citizens.”

But that data focuses on the actions of individual officers rather than the effects diversification has on a police department as a whole. Those effects are less equivocal, if anecdotal.

According to Sklansky, there are two main benefits when a department integrates. First, the community tends to trust police officers more, leading to more effective policing. “When the police force integrates and begins to look more like the community it’s policing, it removes one big impediment toward trust,” Sklansky said in an interview. “It doesn’t guarantee trust, but it removes one thing that makes it hard to develop trust.”

Second, when a department integrates, its culture changes. It becomes less monolithic and less insular, and discussion within the department surrounding racial issues and reforms becomes more likely.

Integration at the level of leadership seems particularly important to attracting minorities and gaining diversity down the chain of command. We can see these effects in Atlanta, one of the few large American cities where African-Americans were overrepresented on the police force in 2010, at 61 percent, compared to 53 percent of the city’s population.

Sergeant M.D. Mitchell explained that at every level of the staff, from the officers to the commander, the Atlanta department seeks to reflect the city it serves. The chief of police, who is black, demands it, Mitchell said.

“If you look at his command staff, his majors, his captains, you have a black or white major contrasting with a black or white captain,” Mitchell said. “It’s the same thing in his command staff, so every race, gender, sexual preference, religion, whatever it is, you can look up in the command staff and identify someone who is the same as you. And if you need to reach out to anyone with a problem, someone in that command staff is similar to you with whom you can have a candid conversation.”

Mitchell’s experience echoes Sklansky’s findings; he said that having a diverse force bleeds out to better policing on the ground, creating better relations with the community. Members of minority communities can look to the police force and see someone they can identify with, Mitchell said. And if they happen to encounter a police officer who is racially or culturally different, that police officer has a co-worker who can explain things. This way, “I learn to serve all the residents of Atlanta,” Mitchell said.

CORRECTION (Jan. 5, 2:35 p.m.): An earlier version of this article incorrectly said the share of whites on police forces was on average 30 percent higher relative to the communities they serve, when it is in fact 30 percentage points higher.