Mass shootings have become more frequent

Mass shootings such as that carried out Wednesday night in Charleston, S.C., not only seem to have become more commonplace: Research on injury prevention shows that they have become more frequent, and more deadly, over the last three decades.

Defining mass shootings as outbreaks of firearms violence in which four or more victims were killed and the shooter was unknown to most of his victims, researchers from Harvard’s School of Public Health and Northeastern University found that, in the roughly two-year period that ended in September 2013, a mass shooting occurred on average every 64 days.

In the preceding 29 years, such shootings occurred on average every 200 days.

In the 10 years leading up to the September 2013 shooting in Washington’s Naval Yard, mass shootings claimed the lives of 285 people. In the period leading up to that (between November 1991, when such data was first recorded, and December 2004), 151 people perished in such attacks.

Between Jan. 1, 2014, and May 26 this year, 195 more people in the United States have been slain in an additional 43 instances of mass shootings, according to statistics drawn from the wiki site Mass Shootings Tracker.

Some, including people opposed to gun-control measures routinely proposed in their aftermath, dispute the contention that mass shootings have escalated. Shooting sprees by criminals are a constant on the American landscape, now made more visible by the nation’s 24-hour news cycle.

That’s not correct, says Stephen Teret, director of the Center for Law and the Public’s Health at Johns Hopkins University in Baltimore.

“The data are good, the data are valid,” Teret said. “It’s not that they were always occurring and we weren’t aware of them. People have been collecting these data for a long time.”

Teret said that the growing circulation of semiautomatic weapons in the civilian marketplace may have played a role in making mass shootings more deadly. But he said that effect would be reflected in trends that have been seen over decades, not in the last few years alone.

But although the fatalities in mass shootings are dramatic, they are dwarfed by the numbers killed by firearms in attacks that affect one or two victims at a time, which garner far less news coverage. The Centers for Disease Control and Prevention estimated that in 2013, 11,208 died in homicides involving firearms in the United States.

“If you look just at numbers, the steady drip of gun deaths on a daily basis far exceeds the number of people killed in mass shootings,” Teret said.

That doesn’t mean we shouldn’t be concerned about mass shootings, particularly after Wednesday’s shootings in Charleston, he said. The media attention that such shootings receive may set off a contagion of violence, inspiring copycat attacks and contributing to casualties.

“If each mass shooting increases the risk of the next mass shooting, we need to pay close attention to that,” Teret said.

And mass shootings may appear to have escalated even faster. For data-keeping purposes, the FBI long set the definition of a “mass shooting” as one in which at least four people were killed. President Barack Obama in 2013 ordered that mass shootings would, in future, be defined as those in which three or more died. (By that accounting, 284 people died in mass shootings between the end of 2013 and May 26 this year).