The warnings began even before Bill de Blasio was sworn in as New York City’s mayor in January 2014. A safe New York depended on the aggressive policing tactics that began in the 1990s and flourished under Mayor Michael Bloomberg and his police commissioner, Ray Kelly. Without those tactics, the doomsayers said, the city would be swamped by a 1970s-style crime wave.

After a federal judge ruled in 2013 that the Police Department’s “stop and frisk” policy was so sweeping that it violated the Constitution, Mr. Kelly was furious. “Violent crime will go up,” he said on NBC’s “Meet the Press.” “No question about it.”

That prediction has, of course, been proved wrong, as crime in the city remains at historic lows under Mayor de Blasio and his police commissioner, William Bratton, even as arrests, stops and summonses continue to plummet after a peak in 2011.

An illuminating new report released by the John Jay College of Criminal Justice provides the most comprehensive analysis yet of the numbers behind the rise and fall of police “enforcement actions” over the past decade. Between 2011 and 2014, the report found, the total number of these actions — defined as arrests for felonies and misdemeanors, criminal summonses, and stop-and-frisks — fell by more than 800,000, or 31 percent.