If there’s one issue that won Bill de Blasio the New York Democratic mayoral primary in September, on his way to a crushing 74 percent to 24 percent victory in the November general election, it was his full-throated opposition to “stop and frisk.” Under this policy, police officers stop, question, and frisk people they deem suspicious, usually with zero evidence that they’ve committed a crime. De Blasio’s predecessor Michael Bloomberg and his GOP election opponent Joe Lhota strongly defended stop and frisk, arguing that it helps reduce the crime rate. But the voters of New York had clearly had enough of a policy that, in practice, overwhelmingly targets minorities, especially young blacks, only a tiny fraction of whom are ever found to be carrying drugs, or a gun, or indeed to have done anything wrong at all.

What few Americans (or at least white Americans) know is that stop and frisk is not limited to New York City. Versions of the policy are in place across the country. And just as in New York, whatever crime-fighting benefits derive from the policy come at the expense of contravening basic American principles of equal treatment under the law and of angering law-abiding minority citizens whose support and cooperation the police need to fight crime.

Until recently, there has been limited data on the degree to which stop-and-frisk policies, as opposed to other factors or police tactics, specifically cause alienation and resentment. But a first-of-its-kind survey we conducted in Kansas City makes that connection quite clear.

Although it is hard to document how widely police departments employ stop-and-frisk-like tactics, the data tells the same story nearly everywhere studies have been done on who is stopped by the police: racial minorities are stopped at considerably higher rates than whites. The underlying reason for this is not racism by individual officers. Rather, it is police department directives requiring officers to make large numbers of stops just to check people out. Police departments widely favor this practice because it allows officers to proactively seize guns and drugs, in officer-initiated stops, rather than waiting to respond to crimes.

Police officers have long checked out people who look suspicious, but in the 1970s several scholars, led by James Q. Wilson, proposed turning this happenstance occurrence into an organized, disciplined practice. In the 1980s, the Reagan administration’s Operation Pipeline, a key war-on-drugs initiative that trained local departments in how to make stops to find drugs, refined the technique and spread its gospel widely across the country. A study by the National Institute of Justice in the mid-1990s showed how to use investigatory traffic stops to seize illegally carried guns. The New York City Police Department then applied the practice to stop and frisks of pedestrians.

Police leaders know that it takes a lot of stops to find just a few illegal drugs or weapons. A widely used police training manual, Tactics for Criminal Patrol, declares that “[c]riminal patrol in large part is a numbers game; you have to stop a lot of vehicles to get the law of averages working in your favor.” Or, as an officer put it to the late journalist Gary Webb, “you’ve got to kiss a lot of frogs before you find a prince.” (The irony in this statement, of course, is that law-abiding citizens are the “frogs” and criminals are the “princes.”) This numbers game helps to explain why 98.2 percent of the stops in New York City yielded no illegal weapon or drugs. This 1.8 percent “hit rate,” as Columbia law professor Jeffrey Fagan has shown, is no better than chance.

To understand the phenomenon outside of New York City, where drivers rather than pedestrians tend to be the target of stop-and-frisk-type operations, we surveyed 2,329 drivers in and around Kansas City, a region typical of large, geographically segregated metropolitan areas in the country. The data from our survey allowed us to distinguish stops to enforce traffic safety laws—like speeding at fifteen miles per hour over the limit—from stops to investigate the driver. Our key finding is that these two types of stops differ from start to finish. In traffic safety stops, based on clear violations of the law, officers quickly issue a ticket or warning and let the driver go. In investigatory stops officers drag the stop out as they try to look at the vehicle’s interior, ask probing questions, and ultimately seek consent for a search (drivers almost always agree, telling us that they feel they have no real choice in the matter).

The key influence on who is stopped in traffic safety stops is how you drive; in investigatory stops it is who you are, and being black is the leading influence. In traffic safety stops, being black has no influence: African Americans are not significantly more likely than whites to be stopped for clear traffic safety law violations. But in investigatory stops, a black man age twenty-five or younger has a 28 percent chance of being stopped for an investigatory reason over the course of a year; a similar young white man has a 12.5 percent chance, and a similar young white woman has only a 7 percent chance. And this is after taking into account other possible influences on being stopped, like how you drive. Police focus investigatory stops on younger people, and so as people grow older they are less likely to be stopped in this way. But a black man must reach fifty—well into the graying years—before his risk of an investigatory stop drops below that of a white man under age twenty-five. Overall, black drivers are nearly three times more likely than whites to be subjected to investigatory stops.

Being black is also the leading influence on how far police officers pursue their inquisition in investigatory stops. In these stops, full-blown vehicle searches are relatively common. After taking into account other possible influences, black drivers in our survey were five times more likely than whites to be subjected to searches in investigatory stops. Searches are remarkably rare in traffic safety stops, and the driver’s race has no influence on whether the driver is searched in these stops.

These differences are not lost on African Americans. According to our survey, African Americans view normal traffic stops as legitimate exercises of law enforcement, and do so at about the same rate as whites do. Indeed, the main difference is that blacks, unlike whites, are even more likely to view a traffic stop as legitimate when the officer lectures them on driver safety, taking that lecture as a reassuring cue that they were in fact stopped for their behavior, not for the color of their skin.

By contrast, African Americans view investigative stops far more harshly, for reasons that are obvious when you hear their descriptions of the experiences, as we did conducting our survey. One gentleman, Billy, told a story about how, on the way to a job interview in Des Moines, he was pulled over by a Missouri highway patrolman for speeding even though he was going, at most, two miles over the speed limit. The trooper made Billy get out of his car and put his hands on the hood while he searched his car. Finding nothing, explained Billy, the trooper “came back and said, ‘The reason why we checked your car is we’ve been having problems with people trafficking drugs up and down the highway.’ So that was that.” It was not the only time this happened to Billy. On another occasion, he, his wife, and his cousin were pulled over on their way to visit an ill relative and their rental van was searched for drugs by a Missouri sheriff’s deputy.

Another man, Joe, told of being pulled over in Kansas City by an officer who drew his gun, handcuffed him, searched his car, checked his license, then let him go with “no ticket, no nothing.” Asked why he thought the officer had stopped him, Joe said, “I don’t know why, beside driving a nice vehicle, a nice car in the wrong neighborhood.” Joe, too, experienced much the same thing a second time, when an officer pulled him over and checked his license for outstanding warrants (he had none). “I felt violated,” Joe says of that episode. As well he should; warrant check stops are in fact illegal. But in some high-crime areas, an officer in a Kansas City-area department told us, “We stop everything that moves.”

The numbers game that police play with investigatory stops is a recipe for giving offense to large numbers of innocent people. Pervasive, ongoing suspicious inquiry sends the unmistakable message that the targets of this inquiry look like criminals: they are second-class citizens. The vast majority of black respondents to our survey—64 percent, compared to only 23 percent of whites—said that you cannot always trust police to do the right thing. Twenty-two percent of black respondents agreed with the statement that “the police are out to get people like me.” Only 4.5 percent of whites felt this way. The disproportionate personal experience of these stops among blacks is one source of this trust gap. Another is hearing stories of police disrespect from families, friends, and work and faith networks. Among respondents to our survey, 37 percent of black drivers, compared to 15 percent of whites, reported hearing these sorts of stories from members of their own household.

Investigatory police stops teach the lesson that the police are here to get racial minorities, not protect them. This is what Cornell law professor Sherry Colb calls the “targeting harm” of investigatory stops. It is the message that people like you are targets of surveillance, not the beneficiaries of protection. And while investigatory stops do enable police to find some lawbreakers and get them off the street, they also undermine the minority community’s trust in law enforcement and thereby its willingness to share information vital to good police work. Sixteen percent of black respondents to our survey reported that they did not feel comfortable calling the police if they needed help, compared to only 5 percent of whites.

Police leaders say the solution is to train officers to be more polite and respectful. This is not enough. The people we surveyed certainly prefer to be treated politely in police stops. But investigatory police stops are fundamentally unjust—and, according to our survey, feared—no matter how polite the officer.

A more meaningful solution is one put forth by U.S. district judge Shira A. Scheindlin, who in August ruled that New York City’s stop and frisks, as practiced, violate the Constitution. She ordered the New York City Police Department to better train officers in what kinds of justifications for these stops are constitutionally acceptable and to require officers to report the justification for stops in their own words (as opposed to simply checking a box to indicate the type of justification). Importantly, she also appointed a lawyer to monitor the police department’s implementation of these directives. While her decision was suspended by an appellate court, it offers an excellent analysis of the constitutional problems in the practice of stop and frisk. We hope it serves to guide other judicial decisions.

Still, in our view, the judge’s reform directives do not go far enough. The Constitution, at least as interpreted by the Supreme Court, sets the bar too low with regard to what is an acceptable justification for a stop. Police training already teaches officers to justify a stop with “specific, articulable facts and reasonable inferences there from,” the language in the key Supreme Court decision Terry v. Ohio. It is too easy for officers to provide a right-sounding legal justification for what is, in fact, a stop based on inchoate suspicion.

The solution is to prohibit investigatory police stops. This will require a change in police norms. Police leaders celebrate investigatory stops and the few big busts they yield. Instead, these leaders—the heads of professional police associations, police chiefs, and police trainers—should acknowledge how much these stops cause palpable harm to the person stopped and to trust in the police. Departments should prohibit stops unless justified by evidence of a violation. Officers would still have the authority to make traffic safety stops to ticket or arrest drivers for speeding, blowing through red lights, or driving drunk. They would still have the authority to stop people who fit a clear description of a suspect. What they would not have the authority to do is to stop people out of curiosity or unspecified suspicion.

If law enforcement leaders won’t act on their own, political leaders may force them into doing so. The New York mayor’s race showed that stop and frisk has taxed the patience of a substantial number of voters. Our survey shows that New York City is not the only place where that’s true.