School shootings and mass killings sometimes seem to be spreading across America like a disease. Now, a mathematical analysis of hundreds of past events suggests a disturbing explanation: such high-impact violence may actually be contagious.
Based on multiple data sets spanning events from 1998 to 2013, scientists tracked the timing of mass killings and shootings in the United States. They found that between 20 to 30 percent of mass killings—attacks that cause four or more deaths—seem to happen in clusters that mirror the outbreak of a contagious disease. In other words, out of any four mass killings or school shootings that take place in the U.S., one of them will have been inspired by one that happened in the past.
A few killers actively admit to being influenced by previous murderers, like several school shooters who referenced the 1999 Columbine High School massacre as a factor in their later acts. Sociologists have long suspected that such a link may exist in a considerable number of cases, but it’s been difficult to tell for sure whether murderers were inspired by others—especially when many commit suicide. So in this latest study, Dr. Sherry Towers of Arizona State University and her colleagues set out to try to quantify the effect on a large scale for the first time.
‘Media attention is like a disease vector’
No comprehensive federal database yet exists on mass killings—though Dr. Towers stresses that one is desperately needed—so her team mined other sources of information. The Brady Campaign to Prevent Gun Violence compiled data on 188 school shootings from 1998 to 2013, and on 477 mass shootings (three or more shooting victims but not necessarily deaths) from 2005 to 2013.
To examine mass killings (those with four or more deaths) the researchers used data compiled in a USA Today study that found 232 incidents between 2006 and 2013. The data set was based on reports to the FBI but also on records at local police departments, which often aren’t sent to federal authorities. The USA Today report highlighted many omissions and inaccuracies in the reporting of such crimes, so Towers and her team only included data they could verify.
When reviewed as a whole, the combined data revealed that mass killings and school shootings do appear to create a contagious period that lasts about two weeks, during which time similar crimes are more likely to occur, the team reports this week in the journal PLOS One.
“What we believe may be happening is national news media attention is like a ‘vector’ that reaches people who are vulnerable,” Dr. Towers told CNN. The most vulnerable people, she said, are those who have regular access to firearms. Once “infected” with information about a mass shooting from national media coverage, a person is more likely to commit a similar crime.
Media ‘makes celebrities out of monsters’
The idea that violence might be contagious is not new. Past research shows that suicides often cluster, in a phenomenon known as suicide contagion, or “copycat suicides,” in which vulnerable people are inspired to take their own lives after reading about the details of previous suicides. For example, in 1987, four New Jersey teenagers committed suicide by driving a car into a garage and sitting inside with the motor running. This kicked off a cluster of suicides, with seven additional self-inflicted deaths by carbon monoxide poisoning documented in the immediate aftermath. In an attempt to stop suicide contagion, many media outlets now abide by voluntary reporting standards to not sensationalize suicides.
The authors believe that nonstop news coverage of high-profile killings and the people who perpetrate them likely plays a role in any contagion effect that does exist. Details of these events more easily reach the relatively small number of people disturbed enough to consider committing more, the authors note. This idea is supported by the fact that contagion doesn’t appear to exist for crimes that don’t get as much national attention. The team’s examination of mass shootings involving three or more victims but not necessarily any deaths found no evidence of contagion.
“When at least three people are shot, but less than four people are killed, the media reports tended be local,” Dr. Towers told CNN, which likely explains the lack of statistical evidence for contagion surrounding those events. There are simply not that many people out there who would do these things, she added, and local media coverage does not reach a large enough pool of people. National media coverage, on the other hand, appears to reach enough people to induce a contagion effect.
“It’s the excessive media attention that creates the copycat phenomenon,” Dr. Jack Levin, a criminologist at Northeastern University, told CNN. “We make celebrities out of monsters.” He pointed out that, disturbingly, there are even trading cards, action figures and magazine covers featuring murderers.
Mass shootings correlate with gun ownership, not mental illness
Media coverage is far from the only factor involved, Dr. Towers stresses. According to the study data, access to guns plays a major role, as well. Mass killings and school shootings were significantly more common in states with higher rates of gun ownership. In contrast, states with tighter gun control laws had significantly fewer mass shootings. As the authors point out, this finding is in line with extensive evidence from previous studies showing that gun ownership is linked with higher rates of both homicide and suicide.
“We have so many semi-automatic weapons that can be easily concealed, and taken from the home and used on classmates or whoever,” Dr. Levin told CNN. Indeed, rates of private gun ownership are higher in the United States than anywhere else in the world – twice as high, for instance, as that of Yemen, a conflict-torn nation in the throes of a domestic insurgency. And our gun murder rate is off the charts: to find adequate comparisons, we need to look at countries like Iraq and the Democratic Republic of the Congo.
On average, mass killings involving firearms occur approximately every two weeks in the U.S., and school shootings occur on average monthly, according to the new study. And a 2012 analysis by Mother Jones found that the incidence of mass shootings has increased in conjunction with rising rates of firearm ownership. A 2014 FBI report confirmed this trend, finding that the frequency of mass shootings in the U.S. have jumped from an average of 6.4 incidents annually from 2000-2006, to an average of 16.4 incidents per year from 2007-2014. In just the last three years, the rate of mass shootings has tripled, according to a report released last October by researchers at the Harvard School of Public Health. Between 1982 and late 2011, mass shootings occurred about every 200 days. But after September 2011, the rate of mass shootings increased to about once every 64 days, according to the Harvard researchers.
Meanwhile, one factor that was not found to be associated with the incidence of mass killings and school shootings was mental illness. That’s not surprising, though, as previous research has debunked the myth that mental illness is a risk factor for gun violence.
How the media can help prevent violence contagion
As for the media, certain reporting practices may reduce the likelihood of promoting violence contagion in the wake of mass shootings. Ari Schulman, of the Wall Street Journal, suggests the following:
- Never publish a shooter’s propaganda. “Aside from the act itself, there is no greater aim for the mass killer than to see his own grievances broadcast far and wide,” Schulman writes.
- Hide their names and faces. With the exception of shooters who are still on-the-run, “concealing their identities will remove much of the motivation for infamy.”
- Don’t report on biography or speculate on motive. “Even talking about motive may encourage the perception that these acts can be justified.”
- Minimize specifics and gory details. Publishing a play-by-play of the shooting or describing the shooter in great detail “could help other troubled minds turn abstract frustrations into concrete fantasies.”
- No photos or videos of the event. “Images, like the security camera photos of the armed Columbine shooters, can become iconic and even go viral,” Schulman points out.
- Talk about the victims but minimize images of grieving families. “Reports should shift attention away from the shooters without magnifying the horrified reactions that perpetrators hope to achieve.”
- Decrease the saturation. Confine news reports of smaller shootings to the realm of local media, and decrease total coverage of the rest. “Unsettling as it sounds,” Schulman writes, “treating these acts as more ordinary crimes could actually make them less ordinary.”