Author: Bruce Bower / Source: Science News

Immediately after a 19-year-old shot and killed 17 people and wounded 17 others at a Florida high school on Valentine’s Day, people leaped to explain what had caused the latest mass slaughter.
By now, it’s a familiar drill: Too many readily available guns. Too much untreated mental illness. Too much warped masculinity. Don’t forget those shoot-’em-up video games and movies. Add (or repeat, with voice raised) your own favorite here.
Now the national debate has received an invigorated dose of activism. Inspired by students from the targeted Florida high school, as many as 500,000 people are expected to rally against gun violence and in favor of stricter gun laws on March 24 in Washington, D.C., with sister marches taking place in cities across the world. But a big problem haunts the justifiable outrage over massacres of innocents going about their daily affairs: Whatever we think we know about school shootings, or mass public shootings in general, is either sheer speculation or wrong. A science of mass shootings doesn’t exist.
“There is little good research on what are probably a host of problems contributing to mass violence,” says criminologist Grant Duwe of the Minnesota Department of Corrections in St. Paul. Duwe has spent more than two decades combing through federal crime records and newspaper accounts to track trends in mass killings.
Perhaps this dearth of data is no surprise. Research on any kind of gun violence gets little federal funding (SN Online: 3/9/18; SN: 5/14/16, p. 16). Criminologist James Alan Fox of Northeastern University in Boston has argued for more than 20 years that crime researchers mostly ignore mass shootings. Some of these researchers assume that whatever causes people to commit any form of murder explains mass shootings. Others regard mass killings as driven by severe mental disorders, thus falling outside the realm of crime studies.
When a research vacuum on a matter of public safety meets a 24-hour news cycle juiced up on national anguish, a thousand speculations bloom. “Everybody’s an expert on this issue, but we’re relying on anecdotes,” says sociologist Michael Rocque of Bates College in Lewiston, Maine.
Rocque and Duwe published a review of what’s known about reasons for mass public shootings, sometimes called rampage shootings, in the February Current Opinion in Psychology. Their conclusion: not much. Scientific ignorance on this issue is especially concerning given that Rocque and Duwe describe a slight, but not unprecedented, recent uptick in the national rate of rampage shootings.
Criminologist Grant Duwe has calculated annual rates of U.S. mass public shootings per 100 million people since 1915 (data since 1976 are shown). The average rate of these shootings has increased since the mid-2000s, but not to unprecedented levels.

Defining mass public shootings to track their frequency is tricky. A consensus among researchers is emerging that these events occur in public places, include at least four people killed by gunshots within a 24-hour period and are not part of a robbery or any other separate crime, Rocque and Duwe say. Such incidents include workplace and school shootings.
Overall, mass public shootings are rare, Duwe says, though intense media coverage may suggest the opposite. Even less obvious is that rampage shootings have been occurring for at least 100 years.
Using Federal Bureau of Investigation homicide reports, Congressional Research Service data on mass shootings and online archives of news accounts about multiple murders, Duwe has tracked U.S. rates of mass public shootings from 1915 to 2017.
He has identified a total of 185 such events through 2017, 150 of which have occurred since 1966. (In 2016, he published results up to 2013 in the Wiley Handbook of the Psychology of Mass Shootings.) In the earliest known case, from 1915, a Georgia man shot five people dead in the street, after killing an attorney he blamed for financial losses, and wounded 32 others. Another lawyer, who came to the crime scene upon hearing gunshots and was wounded by a bullet, ended…
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