The Chicago Tribune reports that the past 14 months have been the Windy City's most violent in two decades, with more than 4,300 people shot and over 760 killed.

Nurses at city hospitals are suffering from compassion fatigue, and everyone from Chicago Mayor Rahm Emanuel on down promises to stop the carnage.

Talk is cheap. Will cops and city government get their act together to fight crime? Unfortunately, they have no reason to.

That's because the public fails to hold public leaders accountable for performance. As Patrick Wolf and I show in "Cops, Teachers, and the Art of the Impossible," there is no statistical relationship between a city's homicide rate and whether the mayor keeps or fires the police commissioner. Indeed as one police expert told us it, no prior researcher even bothered to study this since "there is absolutely no correlation with the homicide rates and police commissioner tenure. Everybody knows that."

Top cops get fired for scandals or because mayors dislike them, not when their officers fail to protect the public they are sworn to protect and serve.

Nor do police leaders get fired for police brutality. My co-author Ian Kingsbury finds no relationship between the number of citizens killed by law enforcement officers and the size of Black Lives Matter protests.

That's tragic, because cops can do better. Recently retired New York Police Department Commissioner William Bratton proved it. Bratton led NYPD under current Mayor de Blasio and back in the 1990s under then Mayor Giuliani.

Bratton gained fame for "broken windows" enforcement of minor offenses, and for using real time crime data to mass cops at trouble spots. Yet other cities tried those with little luck. Three largely unrecognized factors led to NYPD's success.

First, even before Bratton NYPD had talent since it recruited nationally rather than just locally, hiring the best. Second, Bratton highlighted precinct leaders who cut crime, making NYPD a learning organization. Third, leaders who didn't learn were shown the door. Bratton replaced two-thirds of precinct commanders with better leaders. Few police commissioners have such power over personnel, and none use it to fight crime rather than reward cronies.

Bratton's reforms brought years of double digit homicide declines. From 1993 to 2014, New York's homicide rate fell from 27 per 100,000 people to 4 per 100,000, about 50 percent below the national average. By 2014 New York had the fewest killings since anyone began counting a half century earlier. In 2015 The Economist ranked New York the 10th safest major city globally. From 1994 to 2014, about 1,300 fewer New Yorkers were murdered annually compared to 1993.

Police shooting of civilians also plummeted. NYPD's 35,000 officers kill about a dozen people annually, nearly 90 percent fewer than in 1970 and 75 percent below the national norm.

Reforming NYPD likely saved over 25,000 lives, disproportionately black lives — something Black Lives Matter activists were too busy calling for Bratton's ouster to notice.

Activist politics combine with city hall politics to explain why no one copies NYPD. Mayor Giuliani fired Bratton as soon as the popular top cop became a political threat. Within NYPD, Bratton's change agent personality won few friends. Only a commissioner who didn't mind making cops and mayors mad would copy Bratton.

That means that police and city leaders in Chicago and elsewhere will talk nice and keep their jobs, while doing nothing to make black lives matter. That depresses those of us who want to heal racial divides, and make American cops the best in the world.

Robert Maranto (rmaranto@uark.edu) is the 21st Century Chair in Leadership in the Department of Education Reform at the University of Arkansas.

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