In now-familiar graphics, both Mother Jones and The Washington Post tells us that mass shootings are occurring with increasing frequency. Here’s the one from Mother Jones:

(c) Mother Jones. Used with permission.

In the image above, the “bursty” distribution of incidents toward the right-hand side of the graph shows that these incidents are closer together in time — a trend made more explicit in the graphic below showing data analysis by the Harvard School of Public Health.

(c) Mother Jones. Used with permission.

Does the increasing proximity of these incidents demonstrate copycat effects?

Very possibly. Research by Arizona State University mathematics research professor Sherry Towers and colleagues suggests that like suicides and homicides, media coverage of mass shootings and school shootings tend to increase similar incidents in the surrounding community.

Terrorism research has found that terror attacks tend to be similarly “contagious.” (For a discussion on what I mean by “terrorism,” see this primer by Brian J. Phillips, who shares the same definition I do.) In an article published in 1980, Manus Midlarsky, Martha Crenshaw, and Fumihiko Yoshida argued that terror “is a highly imitable strategy.” Qualitative research based on various quasi-Marxist groups from the 1960s and 1970s suggests these groups learned from and emulated one another quite deliberately.

More recent research by Alex Braithwaite and Quan Li shows that incidents of terror tend to cluster around particular times and places as well, leading it to have similar “bursty” qualities in both space and time. Recent research by Blake Garcia and Cameron Wimpy has confirmed that anti-government violence tends to spread when people have access to information about violence in neighboring spaces. All these findings would be consistent with emulation dynamics, competition dynamics, or a mix of both.

Why do we observe these copycat dynamics?

Some suggest that incidents of violence “plant a seed” in the minds of those already predisposed to averse behavior, thereby tipping motivated actors into committed ones.

Others blame media coverage. Brigitte Nacos has argued that contemporary information technology makes the contagion of violence easier, expanding the potential geographic distribution of copycat violence. In the era of print media, for instance, the finite space for coverage of numerous violent events necessarily limited the amount of attention devoted to any single attack, thereby limiting incentives to engage in symbolic violence. With internet technology, these limitations are no more.

Easy access to more lethal technology — and knowledge about how to deploy it — may also be partially responsible for contagion of particular attack repertoires, such as bombings or shootings. In essence, they become easier to conduct after others have established and demonstrated the technical know-how required to carry them out. For instance, Michael Horowitz sees the rise of suicide bombing as a function of tactical diffusion across groups with similar dispositions and operational capacities.

Still others suggest that “violent entrepreneurs” are often seeking notoriety, prestige, or status among their own communities. Provocative acts by others might move them into action to steal some of the vicarious attention possible in such close proximity to another grisly act. Alternatively, it may allow them to “out-do” the prior act while the latter is still fresh in the minds of observers.

Finally, because terroristic violence by definition always involves a wider political goal, some have argued that terror is often an attempt to win support within a broader community — a community perhaps marginalized by various forms of oppression. This is especially likely when several groups are vying for popular support and political influence, thereby leading to “clustering” of terror incidents due to the internal competition and rivalry within competing groups.

What’s important is that the imitative effects of mass shootings and terror attacks may not be unrelated to one another. The blurry distinction between what constitutes mass shootings vs. acts of terror means that, functionally, those motivated to obtain notoriety or political power through graphic violence may not really care whether their competitors are “terrorists,” “shooters” or something else.

Even when investigators discover political motivations for mass shootings after the fact, it’s not always clear whether an assailant meant to further those political goals through the act of violence. In studies involving multiple different types of violence, Gary Slutkin has found that violent acts tend to spread like “a contagious disease,” increasing other forms of violence. This finding prompts him to frame all forms of violence as public health issues that necessarily reinforce one another.

Similarly, other studies suggest that acts of terror often occur in the context of contentious moments within society — increases in different forms of violence can signal larger trends of polarization, discontentment, disruption, and despair. Reduce the latter trends, reduce the violence.

Now for some perspective. Although mass shootings have increased in recent years, it’s important to keep in mind that gun homicides have been declining steadily since the 1980s. Moreover, Americans tend to greatly exaggerate the likelihood of being the victim of terror within the United States (as compared to, say, being killed by their furniture or any number of other causes of premature death ).

Notwithstanding last summer’s attacks in Chattanooga and Charleston, last week’s attacks on Black Lives Matter activists in Minnesota and Planned Parenthood in Colorado Springs, and (possibly) the San Bernadino attacks, multi-casualty terror attacks within the U.S. have become exceedingly rare.

But regardless of the facts, the public’s heightened anxiety and expectations of more terror are, themselves, troubling. Consider this observation about why violence clusters in space and time, as noted by Midlarsky, et al some thirty-five years ago:

For all of these instances of violence, then, the common element may the presence of socialized norms of nonviolent behavior which are eroded by time and exposure to violence until violence becomes a routine and imitable process (296).

In other words, the fact that many people appear resigned to mass shootings and other forms of violence as “the new normal” in the United States could be part of the problem, not part of the solution.

None of these recent killings was inevitable; all were probably preventable. Concerted efforts to reinforce norms and practices of nonviolent behavior in all communities are certainly necessary. So is a thorough national conversation about: (1) what our society is doing to stop mass violence; (2) what our society cannot or will not do to stop mass violence; (3) what our society does that allows (or even encourages) mass violence to take place;  (4) and what, if anything, our society can do to prevent violence and terror from impressing hopelessness upon the nation’s collective imagination.

Without concerted effort to reinforce norms and practices of nonviolent behavior in all communities, more violence — not less— may be on the horizon.