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Mass killings spread like a disease — and a federal ban makes it hard to find the cure

Earlier this year, researchers reached a terrifying conclusion: School shootings and mass killings are contagious, so the occurrence of one tragic event can lead to another. To make matters worse, the researchers said it's hard to know how, exactly, to stop this contagion — because a federal ban on research dollars for gun violence makes it hard to study the issue.

In the study published in PLOS One in July, Arizona State University researcher Sherry Towers and her colleagues found that mass killings and school shootings are more likely to happen in brief clusters of time. The finding suggests that these shootings spread like diseases — essentially, some people hear about a mass shooting through widespread media coverage and decide to carry out their own brutal attacks.

Given this past year's mass killings in South Carolina, Oregon, and California, and the troubling findings, I reached out to Towers to find out what could potentially stop this contagion.

Towers told me the media can play a role. When a shooting gets national coverage, it seems more likely to trigger a kind of contagion effect. So by widely covering these events, the media might make them more likely to happen again.

At the same time, it's in the public interest to cover these stories. These tragedies can highlight, for example, America's extraordinary problem with gun violence. The coverage can also make people more vigilant. For example, after a man in June shot and killed nine people in a predominantly black church in Charleston, South Carolina, the North Carolina florist who tipped off police to his whereabouts said she recognized his distinctive haircut from pictures in news reports.

So how does the media balance these issues? Towers didn't provide a hard answer, but she said, at the very least, coverage should focus more on the broader context and the national policies that could help prevent more mass shootings from happening in the future. At the very least, that could serve the broader public good.

What about other solutions? Towers said it's hard to know: Since 1996, Congress has effectively banned research on gun violence — and that's keeping us ignorant of what the solutions are to mass killings. While federal agencies can easily fund studies that look into how to make roads, cars, planes, and trains safer, they're severely limited by the congressional ban when it comes to finding out what to do about gun violence.

In other words, even though researchers have demonstrated that restricting access to guns can reduce gun deaths, it's hard to know which restrictions on access — or other policies related to gun violence — would work best because of the research ban.

I spoke to Towers about her study, the federal research ban, and how the media can help prevent these types of killings from spreading. What follows is our conversation, edited for length and clarity.

What the research found: Mass killings and school shootings are contagious

A security guard stands outside Columbine High School 10 years after the shooting there.
A security guard stands outside Columbine High School 10 years after the shooting there.
Marc Piscotty/Getty Images

German Lopez: What did your research on mass killings find?

Sherry Towers: My colleagues and myself, one of our research specialties is modeling contagious diseases. What we do is apply mathematical models that describe the underlying issue of how diseases spread in the population, and we use that to predict disease outbreak or estimate the ways to control these kinds of outbreaks.

In January 2014, I was supposed to have a meeting with a group I work with in Purdue University. Unfortunately, the meeting was canceled that morning because there was a shooting on the Purdue campus — a student walked into a classroom, shot another student, walked out, and waited for the police to arrest him. It occurred to me that day that that was the third shooting that I had heard about in about a 10-day period. So it made me wonder if this was some type of statistical fluke that there was this type of clustering, or if there was some sort of contagion process involved.

I thought perhaps the student has been consciously or subconsciously ideating with the idea of carrying out a shooting based on what he had seen in the news. He never, by the way, stated what his motive was.

"In the school shootings and mass killings, we did find evidence of unusual clustering in time"

I talked to my colleagues about possibly applying our expertise in contagion modeling to this particular topic — to see whether there's evidence of some kind of contagion process in these events. This kind of field — of applying contagion models to social problems — is something that has been emerging in the past few years.

So we took this on. We got data from the Brady Campaign to Prevent Gun Violence, which maintains data on school shootings and mass shootings in the US, which they define as three or more people getting shot, not necessarily killed. We also used a database from USA Today of mass killings in the US, where at least four people are killed. With these two sources of data, we applied our contagion model, looking for unusual clustering in time — more than you would expect from mere random chance.

What we found is that in the school shootings and mass killings, we did find evidence of unusual clustering in time. And those two data sets, the media attention to them was largely national — they tend to be events that capture the public's interest, so oftentimes the coverage is national.

The mass shootings, on the other hand, only got local coverage, because they're so common in the US — they happen on average once a day. In that database, we found no evidence of contagion.

Based on these patterns we saw, it appeared to show evidence of contagion effects. But since mass shootings and local news don't have that, we developed our hypothesis that media is playing a role.

GL: Basically, your findings suggest that national media gives school shootings and mass killings so much attention that these events tend to be contagious nationally. It's not like a disease, which spreads through close, local contact.

ST: Exactly.

You have to realize that these kinds of events — school shootings and mass killings — are actually rare. I realize that mass killings are happening in the US once every two weeks. But the federal population is nearly 320 million people. So the kind of person who would be inclined to do such a thing is actually quite rare in the US population. They have to be mentally ill or disturbed and have access to weaponry.

So it takes national media attention to be able to reach those people in the population who are actually at risk for these kinds of things. They're so rare that it takes broad media coverage.

How the media can help prevent mass killings from spreading

WDBJ employee Karen Loftus gets a hug from Donna Anderson, whose daughter works at the station, after a press conference about the two journalists who were killed on August 27 in Roanoke, Virginia.
WDBJ employee Karen Loftus gets a hug from Donna Anderson, whose daughter works at the station, after a press conference about the two journalists who were killed on August 27 in Roanoke, Virginia.
Jay Paul/Getty Images

GL: Some people have pointed to this research to suggest that mass killers, their identities, their motives, and even mass killings altogether get way too much media coverage. What do you make of that?

ST: The media has First Amendment rights to free speech, just like an individual does. So I think that the media attention should not be regulated. If anything, it should be self-regulation coming from the media outlets. Media actually do that in the case of suicide in big cities — they tend to not cover those because it has been noted that suicides are contagious.

I think it would be a very bad idea for the government to try to regulate the media, because that would go against the US Constitution.

But I think that the media is a business; it produces a product for consumers. In this case, the product is news. If there were not consumers for that product, the media would not be publishing stories on the mass killer topic. The reason that the media publishes stories on these topics is because that the public wants to read them. So I think this is a multifaceted problem and not just what the media does, but also about the public's response and what the public wants to hear about it.

GL: Well, I can tell you that these are definitely some of the most highly trafficked stories on Vox. Every single tragedy of this kind that happens, there's an enormous amount of attention and demand for articles.

ST: That doesn't surprise me at all.

One of the things that my colleagues and I have noticed is our study on mass killings gets way more attention than anything else we've done. There have been studies I've done in diseases and influenza that received national media attention, but it's typically over the course of maybe a week in which it's actually in the news before it dies down.

With this particular study on mass killings, every time there's a mass killing, I get a lot of interview requests. It's actually to the point where I find out when there's a mass shooting in my email, because I check my email more than I check the news over the course of a day. I'll check my email, and there's three interview requests from various reporters, and my heart just sinks, because I know that there's been another one.

GL: So if I want to be a more responsible journalist, what should I do? On one hand, I think these mass killings are tragic, newsworthy events that highlight issues that don't get much attention otherwise, like gun violence. I also think coverage of these events might make people more vigilant, so they're more likely to report suspicious activity. How should I balance that with the findings of your research?

ST: Well, I think the media coverage that I've seen oftentimes focuses on the shooter, that person's life, the firearm that person used, and, sometimes, the victims.

One thing I notice that tends to be lacking is the broader context. For example, there tends to be little focus on the fact that the federal government has a moratorium on gun violence research. There's little focus in the media that there's so much more we could be doing that we don't — not just on the personal level in which people protect themselves, take precautions in school, and the individual response, but our response as a nation to these things.

I mean, there has been a moratorium since 1996 on federal funding for research, and it doesn't get much coverage. We had to do this particular study for free, because we could not get federal funding for research. It had to be the kind of thing we did on the side, while working on our regular research on biological diseases. We had a student who did it for free, and the faculty who worked on this basically donated our time.

We are the only first-world country that has this ban on research funding into this problem.

The federal ban on firearms research is keeping us ignorant about gun violence

A child with an AR-15 rifle. Ryan Houston/Moment/Getty Images

GL: It seems like you're saying that the attention focuses too much on the personal aspects of the shooting — the person's identity and the weapons he used — instead of the broader context.

ST: Right, the broader context of how we would go about preventing this. [Former Rep.] Jay Dickey, who was the original sponsor of the moratorium, wrote to Congress the day before the San Bernardino shooting and said he regrets the fact that he sponsored this bill. He said he did it in response to the gun lobby. He believes now that if gun violence research had been funded over the past 20 years, we might not be having this problem with mass shootings to the same degree as we are having today. He wrote that letter to Congress the day before the San Bernardino shooting, San Bernardino happened, and then Congress voted to once again continue this ban on federal funding. That got very little media attention.

As somebody who's working in research in academia, I find it shocking that there's this taboo thing that we're deeply discouraged as researchers to look into. Because if you can't get funding for it, you just can't afford to do many of these research projects for basically free. So researchers who actually look into this problem are rare in the US.

GL: What else do you think can be done to stop these mass killings, beyond changing media coverage?

ST: Well, that's the problem: We don't know how to intervene in this contagion effect.

While our study is very interesting in the sense that it quantifies what people have long suspected to be true, it's just one study. The number of things that could be explored that would help to understand this problem better are so many that it's beyond the scope of my team to do alone.

In other words, we don't know how to stop the contagion effect, because we haven't done the research. And without federal funding to do this research, we're extremely limited in what we can do.