The last two years have been marked by the widely publicised police killings of unarmed black citizens, including the summer 2014 deaths of Eric Garner in New York City and Michael Brown in Ferguson, Missouri. According to the website mappingpoliceviolence.org, over 100 unarmed African Americans were shot by police in 2015 alone, and unarmed black people were shot by police five times more often than unarmed whites. Meanwhile, a recent study by Nix and colleagues analysed the Washington Post database of fatal police shootings and found a smaller though still significant racial disparity: unarmed blacks were twice as likely as unarmed whites to be shot and killed by police. These deaths sparked public outrage, civil disorder, and strong antipolice sentiment, especially among minority citizens. In August and November of 2014, the unrest exploded into violent riots in Ferguson, Missouri. There have since been several more cases of police shootings and alleged misconduct across the USA, stirring more civil disorder, and demonstrating a potential crisis in US policing.
Concurrent with the rising unrest, recent evidence suggests that the reductions in violent and property crime over nearly two decades have begun to tick upward. Data released by the FBI in September 2016 suggest that there were 1.2 million violent crimes committed in 2015, an increase of 4% on 2014, while almost 15 700 murders were committed, up 10.8% on 2014.
Chicago seems to be one of the epicentres of increases in crime and violence: the city’s police department recorded 762 homicides last year – a level not seen since the late 1990s – up from 496 in 2015. With the violence continuing into 2017, President Trump tweeted in January: “If Chicago doesn’t fix the horrible ‘carnage’ going on … I will send in the Feds!”
But any proposed remedy for the problem requires a sensible diagnosis. Experts have posited several explanations for the rising crime rates, both generally and specifically for Chicago. One explanation, termed the “Ferguson effect”, argues that increasing public scrutiny of police actions after the 2014 Ferguson unrest has led police officers to become more hesitant, less aggressive (e.g., less reliant on stop and frisk), and less willing to engage with citizens via community policing (see, for example, Heather Mac Donald’s book, The War on Cops). FBI Director James Comey has on multiple occasions suggested that increased scrutiny of police has led to less aggressive policing, which may be driving the increases in crime.
Additional testing for evidence of the “Ferguson effect” is needed, but we should not ignore other potential explanations for the increasing crime rates. One possible explanation is trends in firearm availability. In September 2016, New York Police Commissioner William Bratton pointed to the number of guns in Chicago, as well as lax gun laws, as the “core issue” behind the spike in violence in that city.
Chicago is the third most populous city in the USA, and one of the few to make data on individual crimes available to the public. Most other major cities in the USA release only annual data on the most violent crimes, and do not additionally include information on crimes such as battery, which are crimes of aggression that do not involve a deadly weapon. Here, we examine the Chicago crime data to see if there is evidence of a “Ferguson effect”. We also test a competing hypothesis that the availability of illegal firearms can help explain the rise in violence in Chicago.