New Study: Treat Chicago Shootings as Epidemics

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Many of Chicago’s 4,368 shootings last year follow a tit-for-tat pattern of vendetta between people who know each other. What if there was a way to anticipate that and break the chain? A new study says it’s possible to do that, reports CityLab. Researchers Ben Green and Thibaut Horel at Harvard and Andrew Papachristos at Yale used a “social contagion” model and tried to predict gunshot victimization in Chicago between 2006 and 2014. Using police records of people arrested together for the same offense, they mapped a network of 138,163 subjects and looked at the spread of violence within it. Their model, based on those that epidemiologists use to understand contagion, assumed that shootings were likely to spread between co-arrestees, who would have close social ties and engage in risky behavior together.

When they ran probabilities on people linked to a shooting victim, they found that 63 percent of the 11,123 total shootings in the network were part of a longer chain of gunshot victimization. The closer someone was to a victim, the greater the risk of being shot. “Gunshot violence follows an epidemic-like process of social contagion that is transmitted through networks of people by social interactions,” says the study, published by the Journal of the American Medical Association last month. The National Network for Safe Communities, based at John Jay College of Criminal Justice, relies on data like this to identify patterns of shooting and design concrete solutions that police and communities can carry out together, with a focus on minimizing the use of enforcement and offering help to those at risk. Shooting victimization is highly concentrated in small social networks. Another study by Papachristos showed that 70 percent of Chicago’s nonfatal gun violence victims between 2006 and 2014 were found among a network of less than 6 percent of the city’s population.


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