Party to violence predicted
The Chicago police, which began creating the Strategic Subject List a few years ago, said they viewed it as in keeping with findings by Andrew Papachristos, a sociologist at Yale, who said that the city's homicides were concentrated within a relatively small number of social networks that represent a fraction of the population in high-crime neighborhoods.
Miles Wernick, a professor at the Illinois Institute of Technology, created the algorithm. It draws, the police say, on variables tied to a person's past behavior, particularly arrests and convictions, to predict who is most likely to become a "party to violence."
The police cited proprietary technology as the reason they would not make public the 10 variables used to create the list, but they said that some examples were questions like: Have you been shot before? Is your "trend line" for crimes increasing or decreasing? Do you have an arrest for weapons?
Dr. Wernick said the model intentionally avoided using variables that could discriminate in some way, like race, gender, ethnicity and geography.
Jonathan H. Lewin, the deputy chief of the Chicago Police Department's technology and records group, said: "This is not designed to replace the human process. This is just designed to inform it."
The police have been using the list, in part, to choose individuals for visits, known as custom notifications. Over the past three years, police officers, social workers and community leaders have gone to the homes of more than 1,300 people with high numbers on the list. Mr. Johnson, the police superintendent, said that officials were increasing those visits this year, adding at least 1,000 people.
During these visits -- with those on the list and with their families, girlfriends and mothers -- the police bluntly warn that the person is on the department's radar. Social workers who visit offer ways out of gangs, including drug treatment programs, housing and job training.
"We let you know that we know what's going on," said Christopher Mallette, the executive director of the Chicago Violence Reduction Strategy, a leader in the effort. "You know why we're here. We don't want you to get killed."
Uncertain, for now, is the effectiveness. The RAND Corporation is evaluating the city's list, but results are yet to be published. Mr. Mallette said that 21 percent of the people they had succeeded in talking to had sought assistance, and that fewer than 9 percent had been shot since a home visit.