It's fairly easy to predict the spread of an infectious disease.
In general: The more relationships an individual has with sick people, the higher the likelihood that they, too, will get sick. The longer the time since the individual was last exposed, the less likely future infection becomes.
With this in mind, researchers and mathematicians say they've adopted a similar mathematical model to analyze gun violence in Chicago, Illinois. (Chicago had one of its most violent years in 2016: the violence produced 762 homicides last year.) "Social contagion" played a key role in 63 percent of the shootings researchers studied.
The study examined Chicago police data over a period of eight years (between 2006 and 2014); more specifically, it examined the data 138,163 individuals who were arrested during this time period. Nearly 10,000 of those individuals were also victims of gun violence. The demographical breakdown is also worthy of mention:
- 75 percent of these individuals were African American.
- 82 percent of these individuals were male.
- 26 percent of these individuals were part of a gang.
- On average, these individuals were 27 years old by the study's midpoint.
Yale University sociologist Andrew Papachristos sat down with NPR's Cheryl Corley to discuss these findings. The following exchange is particularly enlightening:
CORLEY: The research is an analysis of the social network of individuals who were arrested together for the same offense over an eight-year period. They were trying to understand the patterns of gun violence by literally looking at it like a public health epidemic like AIDS and tracking how shootings spread among a group of about 130,000 individuals.
PAPACHRISTOS: Not only is it an epidemic. We can actually show in our study how it's transmitted and actually 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.
CORLEY: Papachristos thinks this type of contagion study could provide an almost real-time response to shooting outbreaks by analyzing the patterns of shootings, the individuals at risk and sending out people who could intervene - not just the police. Chicago Police Superintendent Eddie Johnson agrees. He supports working with other groups even though the city does plan to hire hundreds more police officers in an effort to fight the gun violence here.
“Say you and I are friends and I’ve just been shot and we’re hanging out. By spending time with me, you’re now being exposed to the risk factors that led to me being shot,” said Ben Green, an applied mathematician at the Harvard School of Engineering and Applied Sciences and study co-author.
The study also found that individuals were more susceptible to gun violence immediately after an "associate" they co-offended with was shot. Victims were shot on average 125 days after their “infector” fell prey to gun violence. “Given that we’re able to identify individuals at high risk, that presents an opportunity to target those individuals for social services,” Green says.
But places are also at risk. According to Charles Branas, an epidemiologist at the University of Pennsylvania who has studied the relationship between human geography and violence, "We should think heavily about places, and how we might change places to interrupt gun violence as a disease." Studies have shown that cleaning up neighborhoods and fixing abandoned buildings has successfully reduced gun violence in formerly violent areas.