What is the system trying to predict?
Chicago’s Strategic Subject List/Heat List is a rank-ordered list of people judged most likely to be involved in a homicide or non-fatal shooting.
Work on the list was inspired by the scholarship of a Yale sociologist, Andrew Papachristos who “didn’t help to create the heat list and hasn’t participated in any related visits, [but] his extensive research into Chicago’s crime problems is the basis for much of what the CPD does with predictive analytics.”
What data are the system's predictions based on?
It’s difficult to determine the exact data that is used in creating the Strategic Subject List.
Despite that, a commonly reported variable is rap sheets — arrest and conviction records. Still, various sources have identified different sets of data the list uses to make its predictions. For example, some have reported that the factors include criminal records, social circles, gang connections, and whether or not that person had been the victim of an assault or shooting.
Per a closed press IACP event in 2014, an initial version of the Heat List used the following variables:
- number of times previously victim of aggravated battery or assault
- number of times co-arrested with a prior PTV [party to violence]
- age at most recent arrest
- number of prior weapons charges (UUW)
- trend in criminal activity (slope)
- gang affiliation
- number prior narcotics arrests
- number of times previous shooting victim
- number of prior violent offense arrests
According to a recent New York Times article, the Heat List/Strategic Subject List: “The police cite proprietary technology as the reason they will not make public the 10 variables used to create the list, but say that some examples include questions like: Have you been shot before? Is your “trend line” for crimes increasing or decreasing? Do you have an arrest for weapons?”
What approach does the system use to make its predictions? How is the data analyzed?
It’s unclear what exact technique the Heat List uses to arrive at its conclusions.
“The novelty of our approach," Dr. Wernick told The Verge, "is that we are attempting to evaluate the risk of violence in an unbiased, quantitative way." He continues: "This is accomplished in a similar manner to how the medical field has identified statistically that smoking is a risk factor for lung cancer. Of course, everybody who smokes doesn't get lung cancer, but it demonstrably increases the risk dramatically. The same is true of violent crime."
According to a recent New York Times article, the Heat List/Strategic Subject list is on its fourth revision.
The first reports in 2014 regarding the Heat List/Strategic Subject List noted that the list was “an index of roughly 400 people.” A Chicago Tribune article noted that the list had “about 420 names … of people who in the worst cases were more than 500 times more likely than average to be involved in violence.”
However, more recent reports suggest that the list has more than tripled in size. According to a May 2016 New York Times article, the Heat List/Strategic Subject List “about 1,400 are responsible for much of the violence … all of them are on what the department calls its Strategic Subject List.”
How is information presented to users?
The software apparently doesn’t routinely provide information automatically to officers in the field. Instead, staff who operate the computer model translate the list into specific operational guidance for officers.
How accuracte are the predictions? How is accuracy defined and measured?
Which departments are using the system?
We believe this system is currently being used solely in Chicago.
How do departments use the system?
Chicago police appear to still be determining how they will use the heat list. So far, the list has been used on a pilot basis to “notify” listed people that they are on the list — a process called “custom notification.” As the New York Times reports:
“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, says that officials this year are stepping up those visits, with at least 1,000 more 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 ways out of gangs, including drug treatment programs, housing and job training.”