For a time in 2013 and 2014, The Daily Beast tracked school shootings. At the end of 2013, as we approached the two-year anniversary of the Sandy Hook massacre, we published an analysis of that count. But less than a day later, our statistics were out-of-date after an Arapahoe High School senior in Colorado brought a shotgun and molotov cocktails to school and randomly shot and killed 17-year-old Claire Davis before turning the gun on himself.
Whether covering or following the very American ritual of mass killings with guns (which occur about every two weeks in the U.S.) and school shootings (on average monthly), it can feel like the violence comes in heavy waves, then ebbs long enough for us to get our bearings before the next deluge.
A new study from a team of researchers at Arizona State University may explain the sense of déjà vu that follows such events and our impulse to brace for the next violent act. Mass killings and school shootings in the U.S., the researchers found, actually appear to be contagious—that is, clustered in time.
Led by Dr. Sherry Towers, a statistician and research professor at ASU, the team fit a mathematical contagion model—often used for analyzing the spread of infectious diseases—to existing shooting data collected by private groups, the Brady Campaign to Prevent Gun Violence, and USA Today. They found that mass shootings (where four or more people are killed) and school shootings increase the incidence of similar events within 13 days. According to their research, roughly 30 percent of mass killings take place within contagion periods, and 22 percent of school shootings.
This clustering, Towers’ research suggests, might be due to a process whereby in the immediate aftermath of a school or mass shooting, the media coverage might produce ideation in someone else and increase the probability of another event.
The study also showed a state’s prevalence of firearm ownership significantly correlated with the likelihood of mass shootings and school shootings. In other words, a finding which researchers have discovered again and again: more guns means more shootings and deaths. The researchers also ran rates of serious mental illness and strength of firearms laws within states through the model, both of which were shown to have little impact on these kinds of shootings.
Towers came about this project because of the very same hunch the rest of us often have about the successive nature of gun violence. She was on campus at Purdue University in West Lafayette, Indiana, when a student entered an adjacent building and stabbed and shot dead senior electrical engineering student Andrew Boldt. “It occurred to me that day that there had been three other school shootings in the news just the week prior. The statistician in me wondered, is this just a statistical fluke or do these things cluster?”
Since 1974, studies have supported the idea that copycat suicides are real, something known in sociologist circles as “The Werther Effect” and confirmed in a groundbreaking study in the Lancet Psychiatry journal last year. This research is based on social learning theory—the idea that a vulnerable person sees in the news a suicide of someone with whom they may identify and thinks, even subconsciously, that suicide sounds like a good alternative for himself as well.
Could the same really be true for gun violence?
“There is some evidence that some of them seem to be inspired by events in the immediate past,” Towers said.
Unlike suicide clustering, Towers’ research didn’t uncover any evidence of geospatial clustering, or similar gun violence in the same community after an initial shooting. Additionally, when they looked at less sensational mass shootings, where at least four people were wounded but less than four were killed, the media coverage tended to be confined to local outlets. And in these, the events showed no evidence of contagion. Only in the most violent events that led to the most deaths, or in the more sensationalized coverage of atypical school shootings, did the researchers find contagion.
So it seems to Towers that the more shocking shootings that get national media attention are the contagious events, which isn’t so surprising when you take into consideration the rarity of such extreme violence.
“It’s not that many people that perpetrate these acts,” Towers said. “So if it’s just local media attention, the likelihood that someone who is vulnerable would see the message is much lower than if it’s national media attention.”
The study suggests, but doesn’t yet prove, that high-profile shootings are contagious. The hypothesis is “plausible,” said Matt Miller and Deborah Azrael of the Harvard Injury Control Research Center. “It’s a hard phenomenon to know how to accurately model mathematically,” Miller said.
Both agreed more work needs to be done.
“It would be nice for someone to take this research and take it further and to look at school shootings and find out what kind of coverage they get,” Azrael said. “Most school shootings involve one person being shot, in places where people have access, during arguments. The majority aren’t Columbine. So the next step is really to try and get a handle on the volume of news coverage, and exposure. That seems like a worthwhile thing to do.”