Such stops happen more frequently in minority neighborhoods because that is where the vast majority of violent crime occurs  and thus where police presence is most intense. Based on reports filed by victims, blacks committed 66 percent of all violent crime in New York in 2009, including 80 percent of shootings and 71 percent of robberies. Blacks and Hispanics together accounted for 98 percent of reported gun assaults. And the vast majority of the victims of violent crime were also members of minority groups.

Non-Hispanic whites, on the other hand, committed 5 percent of the city’s violent crimes in 2009, 1.4 percent of all shootings and less than 5 percent of all robberies.

Given these facts, the Police Department cannot direct its resources where they are most needed without generating racially disproportionate stop data, even though the department’s tactics themselves are colorblind. The per capita rate of shootings in the 73rd Precinct  which covers Brooklyn’s largely black Ocean Hill and Brownsville neighborhoods  is 81 times higher than in the 68th Precinct in largely white Bay Ridge. Not surprisingly, the per capita stop rate in the 73rd Precinct is 15 times higher than that in the 68th.

Crime rates are not the only thing that drives police strategy  so do requests for assistance from communities besieged by lawlessness. If residents of an apartment building ask their precinct commander to eliminate the drug dealing on their street, officers will likely question people hanging out around the building and step up their enforcement of quality-of-life laws, resulting in more stops. Requests for crackdowns on street sales come far more frequently from minority neighborhoods, because that is where most open-air drug dealing occurs.

Some critics charge that the more than half a million stops last year indicate that the department is out of control. But the ratios of stops to population and of stops to total arrests in New York are very close to those in Los Angeles, where last summer a judge lifted a federal consent decree under which the police department had operated for the last eight years. The police stop data in Los Angeles are as racially disproportionate as New York’s, yet the judge deemed them consistent with civil rights.