It happened again. This time, gunmen in El Paso, Texas and Dayton, Ohio murdered 31 people and injured at least 50 more in separate mass shooting attacks within 13 hours of each other Saturday night and Sunday morning. It was, in many ways, just another weekend in America, the only nation in the developed world where horrific gun massacres regularly occur. Though nothing new, the frequency of such public mass shootings appears to have accelerated over the past five years, along with larger and more tragic death tolls. According to one recent analysis by The Washington Post, a mass shooting event has claimed the lives of four or more people every 47 days since June 2015. In the mid-’90s, such attacks happened just twice a year, on average.
But this surge in public executions has not swept across all corners of the country equally. Hawaii, for instance, hasn’t seen a mass shooting since 1999. Florida, on the other hand, has had six such incidents, defined by the US government as four or more people killed by a single individual, in the last three years alone, according to data from the nonprofit Gun Violence Archive. And like other forms of gun violence—including homicide, suicide, and unintended accidents—researchers are finding that mass shooting events happen more often in states with looser gun laws.
Because while Congress may not have passed any national gun laws in the aftermath of past mass shootings, individual state legislatures have. And as the disparity between states with weak gun laws and those with tough ones has widened, so too has the gap in mass shootings. Which means that terrorist acts like those committed in El Paso and Dayton over the weekend are more likely to keep happening to people who live in places where it’s easy to buy, sell, and carry guns. The country is splitting into the gun law-haves, and the gun law have-nots, and deadly statistics are now revealing the impact those policy decisions have on people’s lives.
Studying mass shootings, which make up only a tiny fraction of all gun deaths, has long been tricky, because of their historical rarity and a general dearth of data on guns or gun deaths. (That’s because of research-stifling federal legislation that was only recently overturned.) But one ironic effect of there being more mass shootings lately is scientists now have enough data to start to see trends emerging.
In a paper published earlier this year in BMJ (previously the British Medical Journal), epidemiologists at Columbia University looked back at the Federal Bureau of Investigation’s crime database from 1998-2015 to calculate annual rates of mass shootings in each state. Then they matched that up against each year’s edition of the Traveler’s Guide to the Firearms Laws of the Fifty States—an annual report that tracks any changes to gun laws in all 50 states and rates each one on their permissiveness. Published by a Kentucky attorney-slash-arms dealer for a gun-toting audience, the guide is frequently promoted by the National Rifle Association. States are scored zero (for completely restrictive) to 100 (for completely permissive) based on 13 factors, including the right to carry guns in the open, limitations on the types of guns state residents can own, and whether out-of-state gun permits are recognized.
What the researchers found was that over time states have dug themselves into a bimodal distribution. That is, they’ve self-clumped into two distinct groups—a smaller one made up of eight states scoring between five and 25 and the other, much larger one, clustered around scores from 70 to 100. “One of the most interesting things about this data is that we aren’t seeing a full spectrum, because there just aren’t that many states directly in the middle,” says Paul Reeping, the study’s lead author.
When they compared those scores to mass shootings per million residents, they found that for every 10-point relaxation in a state’s gun laws, the rates of mass shootings in that state increased by 11.5 percent. This trend showed up even after the models were adjusted for population demographics like household income, unemployment, poverty, education, incarceration rates, and race. The eight most restrictive states include Hawaii, Massachusetts, New Jersey, Connecticut, Maryland, California, Illinois, and New York. Leading the pack in both permissive laws and mass shooting rate were Vermont, South Carolina, Louisiana, and Arizona. (Florida, where the Parkland shooting took place last year, was the only state not included in the analysis because it doesn’t participate in the FBI’s Uniform Crime Reporting program.)
Both Texas and Ohio, where the latest terror attacks were carried out, also scored high on gun law permissibility. In both states it’s legal to carry concealed weapons in public, provided the gun owner has the proper permits to own it. In Texas, permits are issued to applicants over the age of 21 who pass a four-to-six-hour training course and don’t have any pending criminal charges. According to Ohio’s gun laws, residents 21 years and older must complete an eight-hour training course, not be addicted to any controlled substances, and be able to pass a criminal background check.
Most relevant to the recent killings in El Paso and Dayton though, is the fact that the semi-automatic weapons used to carry out the attacks can be purchased legally. Only six states and the District of Columbia have enacted bans on these types of military-style firearms. Texas and Ohio are not among them. Both states also allow large-capacity magazines like those the gunmen in both El Paso and Dayton appear to have used to fire dozens of rounds in seconds without having to reload.
It’s worth noting here that while living in a state with strict gun laws does appear to confer some significant public health advantages—fewer gun-related suicides and homicides, one recent study found it cut rates of premature deaths in half—those laws only go so far. Motivated individuals will find ways around them, either over the internet or across porous state borders. The gunman who killed three people in Gilroy, California, in July, for example, traveled to Nevada to buy a military-style rifle configured in a way that was illegal in his home state.
And this type of thing happens a lot. Second Amendment activists often point to Chicago, a city with rampant gun violence in a state that has some of the nation’s strongest gun laws. But most of the guns recovered in Chicago were purchased outside Illinois, in neighboring states with laxer laws, according to a 2017 report by the Chicago Mayor’s Office.
But at least according to Reeping’s analysis, the trend of more permissive laws being linked to more mass shootings is actually gaining momentum. Starting around 2010, the data begins really diverging—mass shooting rates dropped in states with restrictive laws as they accelerated in states with more lax ones.
Reeping says this could be related to polarizing trends in gun policy-making, as generally permissive states make their laws more relaxed and restrictive states clamp down tighter and tighter in the face of rising violence. In Texas, for instance, where four of the ten deadliest mass shootings in US history have taken place, ten new pro-gun laws are set to take effect before the end of the month. The associations are strong, though Reeping shies away from suggesting any causality in the data. “There’s so much going on and we can’t control for everything,” he says. But as an epidemiologist he gets frustrated that the American public is willing to believe every study that suggests coffee is associated with living longer or that eating chocolate is linked to lower rates of depression but view the data linking gun laws to gun violence with suspicion.
“Right now we can only do associational studies because there isn’t the money to do the larger, more prospective studies that could answer these questions definitively,” he says. “But even now we have very, very strong indicators based off the number of studies published that more permissive gun laws really do have an effect.”