If you think there's a good chance the police will beat you up, you're less likely to call the cops. Sometimes, this reluctance manifests itself not just in an individual but across an entire community. Sociologists and criminologists call this phenomenon legal cynicism—a basic lack of confidence in the criminal justice system's fairness, competence, responsiveness, and all-around legitimacy. Where legal cynicism flourishes, the theory goes, people tend to withdraw from the formal crime-control system; and in the U.S., legal cynicism is most likely to flourish in low-income minority neighborhoods.

A trio of sociologists has just found an ingenious way to measure this effect. In a new study for the American Sociological Review, Matthew Desmond of Harvard, Andrew Papachristos of Yale, and David Kirk of Oxford note that research on this subject usually relies on surveys and interviews, methods that can reveal a lot about people's attitudes but "are less reliable when it comes to measuring interactions with the police." So instead they selected a high-profile example of abusive police behavior—the 2004 beating of Frank Jude, a black Milwaukee man assaulted by a group of white officers—and then located and counted the city's 911 calls after news of the beatdown broke. Controlling for various variables, they found a small, brief decline in calls in predominantly white neighborhoods and a "large and durable" decline in predominantly black neighborhoods, with the latter lasting more than a year. They then examined Milwaukee's 911 calls following a 2007 police assault on another unarmed black man, Danyall Simpson; that too produced a decline.

The authors also wondered whether nationally reported incidents in other cities could produce the same result. Here the results were mixed. 911 calls went down in Milwaukee, especially in black neighborhoods, after the 2006 shooting of Sean Bell in Queens. But the 2009 death of Oscar Grant in Oakland did not produce the same result.

These results have interesting implications for the debate over the so-called Ferguson effect. Usually that phrase refers to the idea that increased scrutiny has made cops wary about policing proactively, leading to increases in crime. But as I noted here after the FBI released last year's crime statistics, there is a rival theory that focuses not on the supply of policing but the demand for it. Richard Rosenfeld, a criminologist at the University of Missouri–St. Louis, thinks legal cynicism may help explain several cities' recent spikes in homicides. "Lack of confidence in the police among African-Americans predates the recent police killings in Ferguson, Cleveland, New York and elsewhere," he wrote earlier this year. "But it is likely to be activated by such incidents, transforming longstanding latent grievances into an acute legitimacy crisis." When people don't trust the police, they are less likely to cooperate with them—and more likely to turn to do-it-yourself alternatives to policing, such as the violent resolution of disputes. (It is certainly possible to think of alternatives to calling 911 that do not entail doling out rough justice. And it is wonderful when they flourish. But they require work, trust, and time to be effective, just like a police department does.)

Desmond, Papachristos, and Kirk's work lends theoretical support to Rosenfeld's theory, though obviously they're not looking at the same time period. It also has implications for another question raised by 2015's crime numbers: Why did homicides rise so much more than violent crime in general? (According to the FBI, violent crimes increased 3.1 percent last year. Homicides went up 10.8 percent.) Since murder is the most serious crime around—and since it's easier to ignore an assault than to hide a dead body—killings are reported much more consistently than other offenses. It is entirely possible that those other crimes surged more sharply than the official statistics suggest.

It is also entirely possible that the authorities will respond to those increases by unleashing the very sort of policing that fuels legal cynicism, thus feeding the cycle.