Is gun violence catching?

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Guns for sale at a Houston gun show. View full image

With over 10,000 individuals shot and killed each year by another person, and 60,000 injured by firearms, the United States has the highest rates of gun violence among high-income countries—violence that appears to be both pervasive and random. But, according to a recent study by a team that included associate sociology professor Andrew Papachristos, gun violence is not random. Rather, it’s concentrated within relatively small social networks, and it’s replicated through a process of social contagion.

Social contagion, Papachristos explains, is the process by which people in the same social network profoundly affect each other’s feelings, ideas, and behaviors. “Contagion via social ties,” he says, “means that, when someone in your social network becomes a subject of gun violence, your risk increases.”

The study, published in JAMA Internal Medicine, was an epidemiological analysis of 138,163 individuals arrested in Chicago between 2006 and 2014. In examining connections among people arrested together, the researchers found that over 63 percent of gunshot violence episodes could be attributed to social contagion. Individuals within these social networks were at greatest risk of being shot within about 125 days after those most responsible for exposing them to gun violence—their “infectors”—had been the subject of gun violence themselves.

Demographic factors play a role: gun violence tends to concentrate among young men of color within economically disadvantaged urban communities. But those factors alone don’t explain how it spreads, or predict who is likely to become a victim.

The patterns revealed in the study offer new ways to think about prevention. “Tracing violence episodes through social networks could provide valuable information not only for law enforcement,” says Papachristos, “but for public health and medical professionals to create effective interventions with people and communities at highest risk.”