Protesters march in Ferguson, Mo., in August 2014 after the shooting of Michael Brown, an unarmed black 18-year-old. (Jeff Roberson/AP)

Alongside the Black Lives Matter movement in the past several years, civil rights advocates have begun pointing out that the way municipalities collect fees and fines often disproportionately affects low-income communities of color, especially when those communities aren’t well represented in local governments. In 2015, as a follow-up to investigations of police bias in Ferguson, Mo., the Civil Rights Division of the Justice Department released the Ferguson report, which painstakingly documents how the police department in that city relied overwhelmingly on fees and fines collected from people in ways that “both reflect and exacerbate existing racial bias.”

But here’s another result of fee and fine enforcement that has never before been measured: Police departments that collect more in fees and fines are less effective at solving crimes.

Here’s how we did our research

We document this relationship in a recent article. We started with detailed municipal finance data for 2007 and 2012 from the two most recent survey years of the Census of Governments, a Census Bureau survey that collects detailed revenue and expenditure data from cities and towns. We combined that with crime clearance data for those same years from the FBI’s Uniform Crime Reporting Program, which collects crime and policing data from law enforcement agencies nationwide. We could then examine whether departments that are successful at bringing in more municipal revenue are also effective at investigating crime.

Examining nearly 6,000 cities’ finance and crime data for each of the two studied years, we find a strong link between revenue collection and clearance rates. Police departments in cities that collect a greater share of their revenue from fees, fines and civilly forfeited assets have significantly lower rates of solving violent and property crimes.

We suspect that this comes simply from how these police departments focus their time and resources. Departments that need to collect fee and fine revenue shift their officers away from investigatory work. That’s especially true in smaller cities, where we found an especially clear link: Higher revenue from fees and fines meant fewer violent crimes solved. Cities with smaller departments and fewer resources are less likely to have specialized investigators, so when patrol officers are collecting revenue, they’re not investigating more serious crimes.

Here’s an example of how it works

Let’s imagine a city of 50,000 people — call it Middletown — where the per capita income, racial demographics, crime rate and similar variables are the same as the state averages. Nationally, on average, municipalities bring in 2 percent of their revenue from fees and fines. If Middletown’s police department collected only about 1 percent of its revenue from fees and fines, our model predicts it would solve 53 percent of its violent crimes and 32 percent of its property crimes. But if Middletown’s police department instead collected 3 percent of its revenue from fees and fines, our model predicts that clearance rates would fall to 41 percent for violent crimes and 16 percent for property crimes. That’s a stark drop of 12 and 16 percentage points, respectively.

Some communities have a saying: “The police are never there when you need them and always there when you don’t.” Our findings help explain this adage. In cities where police are collecting revenue, communities are at once overpoliced — because they are charged with more fines and fees — and underpoliced — because serious crimes in their areas are less likely to be solved.

This dynamic of simultaneous overpolicing and underpolicing reduces the community’s trust in policing and in government more generally. For many citizens, police interactions may be their only contact with any government official. If citizens see the police in particular and the government in general as exploiting them for revenue, they are unlikely to see either as allies in keeping their communities safe. Low clearance rates, especially for violent crimes, reduce public trust in the police and in government as a whole — leading them not to cooperate with either.

A good example of this in popular literature is Jill Leovy’s “Ghettoside,” which focuses on homicide policing in Los Angeles. A vicious circle can emerge when police cannot or do not solve crimes, especially violent ones. Communities lose trust in the police, making it less likely that they’ll help the police solve crimes, which, in turn, increases the number of unsolved crimes.

Almost 40 years ago, James Q. Wilson’s “Varieties of Police Behavior described different “styles” of policing that departments develop. Some are aggressive, some not. Some are more courteous, some not. Some focus mostly on crime, while some take a broader view of their work. Our research shows that a municipality’s revenue approach can shape its police department’s style. When police are also revenue collectors, that shapes how citizens, especially poor citizens of color, relate to and perceive them. But it also reverberates in other ways.

Policing practices may be far more interconnected than observers have realized, with each policy choice reverberating in unexpected directions. Reforming institutions so that municipal governments rely less on fines and fees may also help improve police effectiveness and improve  public safety.

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Rebecca Goldstein is a doctoral candidate in the department of government at Harvard University.

Michael Sances is an assistant professor in the department of political science at the University of Memphis.

Hye Young You is an assistant professor in the Wilf Family Department of Politics at New York University.