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From the New York Times:
By JEFF ASHER and ROB ARTHUR JUNE 13, 2017
Gun violence in Chicago has surged since late 2015
To translate that out of Passive Voice-ese: Since Mayor Rahm Emanuel caved in to Black Lives Matter and released video of a bad shooting by the Chicago Police Department on November 23, 2015, blacks have been shooting blacks in huge numbers in Chicago, while, presumably, policemen have become even more expert on comfortable positions for sleeping in their cruisers along the lakefront near my old condo.
, and much of the news media attention on how the city plans to address this problem has focused on the Strategic Subject List, or S.S.L.
The list is made by an algorithm that tries to predict who is most likely to be involved in a shooting, either as perpetrator or victim. The algorithm is not public, but the city has now placed a version of the list — without names — online through its open data portal, making it possible for the first time to see how Chicago evaluates risk.
We analyzed that information and found that the assigned risk scores — and what characteristics go into them — are sometimes at odds with the Chicago Police Department’s public statements and cut against some common perceptions.
■ Violence in the city is less concentrated at the top — among a group of about 1,400 people with the highest risk scores — than some public comments from the Chicago police have suggested.
A big problem with Chicago’s predictive algorithm is that Chicago clears so few homicides that it mostly has data on victims of crime rather than perps. From the Chicago Tribune last summer:
Chicago police currently solve about 30 percent of the city’s homicides, said a department spokesman, Anthony Guglielmi. In Houston, a city of comparable size, that figure is 56 percent, according to a spokesman for the Houston Police Department. In Philadelphia, it’s 49 percent.
Those figures — known as the clearance rate — include homicides marked as solved in the current year but committed in different years. But when old cases are stripped out, Chicago’s clearance rate for 2016 homicides drops to about 21 percent. In all, Chicago police had solved just 92 of 432 homicides committed in 2016 through Aug. 16, according to police statistics.
Looking at victims is helpful in predicting future crimes because it turns out that a lot of victims of crime were victimized because they were criminals themselves.
I can’t tell whether the CPD database keeps track of people arrested together, or, say, passengers in a car who weren’t arrested when one passenger was hauled off to jail, or who were accompanying the victim of a crime, but that kind of information would seem useful in constructing social network maps to get a sense of who might go looking for vengeance.