But according to a 2015 paper out of Arizona State University, “Contagion in Mass Killings and School Shootings,” there are some data that mass shootings often occur in bunches, which indicates that they “infect” new potential murderers, not unlike a disease. “We find significant evidence that mass killings involving firearms are incented by similar events in the immediate past,” the authors wrote. Suicide and terrorism, too, have been found to be likewise contagious. (Interestingly, the authors found “no significant association” between the rate of school and mass shootings and the state’s prevalence of mental illness.)

Diseases spread among individuals, but the contagion of mass shootings seems to spread through broadcast media. In an interview with The Atlantic in 2015, Sherry Towers, the ASU paper’s lead author, hypothesized that television, radio, and other media exposure might be the vectors through which one mass shooting infects the next perpetrator. Like a commercial, each event’s extraordinary coverage offers accidental advertising for depravity. One reason why mass-media coverage of shootings might inspire more shootings is that public glorification inspires some mass murderers. Eric Harris, the central planner of the Columbine murders, wrote Ich bin Gott—German for “I am God”—in his school planner.

It’s hard to say what lessons the news community should take from such findings. Mass shootings have inherent and unambiguous news value. It is absurd to suggest that the media ignore them entirely. But perhaps journalists should cover such events with an awareness that even noble coverage can advertise. Some media critics endorse a “Don’t Name Them” method, whereby mass shooters are deliberately left anonymous. But readers and viewers are fascinated by the motives and details of mass shootings, and it’s unlikely that they’d tolerate such an approach. With that in mind, Mother Jones has suggested minimizing the use of the perpetrator’s name, limiting head shots, and banning outright any potentially aggrandizing photos.

The mass-shooting-contagion paper ought not to be the final word on the effect of mass media on gun violence. The United States spends millions of dollars tracking other causes of disasters, such as tornadoes, which have been about as deadly as mass shootings in the past half-century. But research on mass shootings is relatively sparse.

That might explain why there aren’t standard methodologies, definitions, or even conclusions about their frequency or causes. For example, an analysis by Mother Jones starting in 2012 found that mass shootings killing four or more people have become more frequent in the past few decades. But a separate analysis by Grant Duwe, the research director at the Minnesota Department of Corrections, found that while the mass-shooting rate has not increased since the 1970s, the number of victims has grown steadily since the early 2000s. Duwe supposes that the rising deadliness of mass shootings might be most responsible for the growing perception that these events are becoming more common, since the number of casualties is the strongest predictor of media coverage. It’s a scary story, no matter which side is correct. Given the contagion research, one can imagine a sinister feedback loop that might explain the recent spate of murderous sprees. If more victims mean more media coverage, and more coverage means more inspiration, it implies that historically violent mass shootings might be the most contagious.