Mass Shootings Can Be Contagious, Research Shows

Author: Rhitu Chatterjee

There were three high-profile shootings across the country in one week: The shooting in Gilroy, Calif., on July 28, and then the back-to-back shootings in El Paso, Texas, and Dayton, Ohio, this past weekend. 

That's no surprise, say scientists who study mass shootings. Research shows that these incidents usually occur in clusters and tend to be contagious. Intensive media coverage seems to drive the contagion, the researchers say.

Back in 2014 and 2015, researchers at Arizona State University analyzed data on cases of mass violence. They included USA Today's data on mass killings (defined as four or more people killed using any means, including guns) from 2006 to 2013, data on school shootings between 1998 and 2013, and mass shootings (defined as incidents in which three people were shot, not necessarily killed) between 2005 and 2013 collected by the Brady Campaign to Prevent Gun Violence. 

The lead researcher, Sherry Towers, a faculty research associate at Arizona State University, had spent most of her career modeling the spread of infectious diseases — like Ebola, influenza and sexually transmitted diseases. She wanted to know whether cases of mass violence spread contagiously, like in a disease outbreak. 
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So, she plugged each data set into a mathematical model.

"What we found was that for the mass killings — so these are high-profile mass killings where there's at least four people killed — there was significant evidence of contagion," says Towers. "We also found significant evidence of contagion in the school shootings."

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