Every mass shooting in the U.S. raises calls for better policies to prevent such tragedies. There's evidence suggesting that certain kinds of laws may reduce deaths from mass shootings, say scientists who study the field — but those policy options are not the ones usually discussed in the wake of these events.
The body of research scientists have to draw from is limited, notes Michael Anestis, executive director of the New Jersey Gun Violence Research Center at Rutgers University. "Mass shooting research is a very small portion of gun violence research," he says.
That's because mass shootings account for less than 1% of the roughly 40,000 people killed by guns each year in this country, Anestis explains. "They're horrific, they are all too common, and yet, it's just the very tip of the iceberg, right?"
Those researchers who do study gun violence tend to focus on the kinds of violence, like suicide, associated with the most deaths, he says. But, he adds, the entire field of gun violence research has long been neglected and hardly funded.
"There is money out there, but it is really far below where it should be given the amount of injury and death and economic costs associated with gun violence," says Anestis. "It's just disproportionally underfunded."
Two approaches worked better than others
Still, some studies have findings about what might prevent mass shootings.
One such study took advantage of the fact that in the U.S., gun laws vary from state to state. "That is, honestly, less than ideal from a public safety standpoint, but it does provide researchers with opportunities," says Daniel Webster, co-director of the Johns Hopkins Center for Gun Violence Solutions.
He and some colleagues recently analyzed more than 30 years of data on shootings in the U.S. that involved four or more victims. They compared states to try to tease out the effect of various gun laws. "I have to acknowledge that this is a really hard and, frankly, inexact science," says Webster.
Despite those limitations, he says, "We did find two policies that had significant protective effects in lowering rates of fatal mass shootings."
One was a requirement that a gun purchaser go through a licensing process. "A licensing process requires someone to, you know, directly apply and engage with law enforcement, sometimes there's safety training and other requirements," says Webster.
Another approach that seemed to reduce deaths from mass shootings was state bans on buying large-capacity magazines or ammunition-feeding devices for semiautomatic weapons.
That makes intuitive sense, says Webster, because these items allow a shooter to fire many bullets in a short amount of time without interruption. If a shooter has to stop and reload, victims could escape or fight back.
There's another study of mass shootings showing that this kind of law seemed to have a protective effect. David Hemenway, director of the Harvard Injury Control Research Center, worked with colleagues to examine the effect of banning large-capacity magazines on almost three decades of mass shootings in different states.
"The states which had bans did much better in terms of having fewer mass shootings, and the mass shootings that occurred were much less lethal in terms of the number of people dying," says Hemenway.
What about background checks or having police at schools?
In the wake of a mass shooting, people often argue for the need for comprehensive background checks, says Webster. He supports that policy but says his research doesn't show that it's linked to a reduction in this particular kind of deadly event.
An additional common refrain after a mass shooting, he says, is a call for policies that make it easier for people to carry guns so they can defend themselves. "Well, guess what, the data do not bear that out at all," says Webster. "If anything, it shows higher rates of fatal mass shootings in response to weaker regulations for concealed carry by civilians."
And while school systems might try to respond to the threat of mass shootings by having police officers on site or having students go through drills, "as far as I know, there's not strong research about any of those things," says Hemenway.
Keeping guns away from young people, whether through safe storage of firearms in a home or age restrictions on purchasing, would be expected to have a protective effect, says Webster, based on data showing that "the peak ages for violent offending with firearms is roughly 18 to 21."
The public health risks associated with young people drinking alcohol inspired a ban on drinking under the age of 21, he says. But the shooter in Uvalde was able to legally buy semiautomatic rifles just after his 18th birthday.
It seems plausible that age restrictions might make it harder for young adults to access weapons capable of creating a mass shooting, says Anestis, but "do we have large data-based resources to evaluate those policies? No, we don't."
One emerging policy option that has some preliminary evidence behind it is allowing police officers to temporarily take guns away from people who seem to pose an imminent danger. A study in California that looked at how this process got used over a two-year period in that state found 21 occasions when it was done in response to threats of a mass shooting — several of which involved schools.
It's not possible to know if taking away those guns actually prevented mass shootings, but researchers say it's still important data given the general dearth of information and limited funding for research. One study in 2017 found that guns killed about as many people each year as sepsis, a life-threatening response to infection, but funding for gun violence research was about 0.7% of that for sepsis.
"There's so many things to study in the gun area, and we've had not nearly enough studies for 25 years," says Hemenway. "Once you scratch the surface right now about what is known, we know so little."
