Social Contagion Helps Explain Chicago Gun Violence, Study Finds

Gun violence is transmitted by networks of socially connected individuals through a process of "social contagion," a study published in the Journal of the American Medical Association finds.

Funded in part by the John D. and Catherine T. MacArthur Foundation and based on an epidemiological analysis of 138,163 individuals in Chicago comprising pairs of individuals arrested together for the same offense, the study, Modeling Contagion Through Social Networks to Explain and Predict Gunshot Violence in Chicago, 2006 to 2014, found that when one co-offender becomes a victim of gun violence, the likelihood of the other co-offender being shot increases. Indeed, social influence of this sort was responsible for 63.1 percent of the 11,123 episodes of gun violence analyzed, leading to the shooting of 9,773 individuals, some more than once. According to the study, co-offenders — who typically share preexisting social ties with their "infector" (the person most responsible for exposing the subject to gun violence) — were shot, on average, 125 days later. In addition, researchers identified 4,107 separate connected chains of infection through  co-offending networks, including 680 chains that involved multiple subjects — averaging 2.7 people but up to as many as 469 — as episodes of violence in one part of the network generated additional episodes.

The study found that a combined model incorporating both social contagion and demographics better predicted which individuals were at highest risk of being shot on any given day than models focused on either factor. The report further argues that gun violence prevention efforts that account for social contagion among connected individuals, as well as demographics, are more likely to help prevent shootings than interventions focused solely on either factor. The report's authors suggest that a holistic public health approach to gun violence be developed in two ways: first, by taking into account the social dynamics of gun violence and tracing the spread of episodes through social networks, with the aim of designing interventions focused on individuals and communities at highest risk; and second, by focusing on the safety of potential victims of gun violence rather than the offenders.

"So if I get shot, for instance, there's a high likelihood that the people around me in my networks will also be victims and that, then, their friends will be victims," Andrew V. Papachristos, one of the study's authors, told National Public Radio. "Not only is it an epidemic; we can actually show in our study how it's transmitted and...specific individuals who may be at risk. And so when you look at the network figures in the study, every one of those little dots is a real human being."