Your neighboring states’ strict gun laws could mean fewer homicides in your county, according to a new study published in JAMA Internal Medicine. Researchers also determined that states with stringent firearm regulations tended to have lower rates of homicides and suicides involving firearms, as well as lower suicide rates overall. They conclude that stricter gun laws at the state level could prevent firearms homicides and suicides in that state and neighboring states.

The debate following the mass shootings in Las Vegas, Sutherland Springs, Texas, and Parkland, Florida—which all occurred in the last five months—has largely focused on the need for nationwide gun regulation. However, the current reality is that firearms regulation varies largely by state and county. Lead study author Elinore Kaufman, chief resident of surgery at New York-Presbyterian/Weill Cornell Medical Center, tells Tonic that when she began her research in early 2015, she wanted to know more about the interaction between local regulations and firearms deaths.

“We were particularly interested in the interaction between deaths in one area and laws in another,” Kaufman says. “Looking at death rates on the county level allowed us to understand the geographic variation better.” For instance, Kaufman notes that a New York resident in the northeastern corner of the state might be more affected by gun laws in Vermont, whereas a resident of southwestern New York might be more affected by laws in Pennsylvania and Ohio.

Such regional interactions have headlined the gun regulation debate for decades. In the landmark McDonald v. City of Chicago case in 2010, the Supreme Court sided 5-4 in favor of overriding Chicago’s handgun ban on the basis of the Second Amendment. Chicagoans who wanted a handgun, however, could get one legally just a few miles away in Northwest Indiana anyway.

“Both Washington and Chicago had pretty good restrictions,” says John Donohue, a Stanford University law professor, economist, and gun violence researcher. “They were both surrounded by areas that were very lax, and that undermined them tremendously.” In reference to Chicago and District of Columbia v. Heller—a 2008 Supreme Court case that struck down the capitol’s handgun ban—Donohue says the nearby region’s laws impacted the effectiveness of local gun regulation. “Which is terrific for the NRA because it shows these types of restrictions don’t do any good,” Donohue says.

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Kaufman’s research challenges the NRA’s assertion that gun laws aren't effective. She examined Centers for Disease Control and Prevention data on firearm suicides and homicides in the 3,108 counties in the continental US between 2010 and 2014, and compared those death rates to state and county firearm policies. (It’s worth noting that gun-related suicides far outnumber homicides: In 2015, there were 12,979 firearms deaths from homicide and 22,018 from suicide.)

Each county got a state policy score, which Kaufman determined by codifying the strength of the state’s firearm laws, and an interstate policy store, used to adjust for population (researchers assumed more populous states were more likely to supply guns to neighboring states) and proximity to neighboring states. Among the rules that determined a state policy score were regulations on how firearms are transferred and tracked, policies on licensing, dealer inspections, and background checks.

They did a statistical analysis, which had multiple conclusions. First, states with strong gun laws had lower rates of firearm homicide in their counties. Counties in states with lax state firearm policies that bordered other states with lax policies saw the highest rates of gun-related homicides. For a county in a state that has lax firearm policies to have low rates of gun-related homicide, it needed to border states with stringent firearm policy. “This may mean that there is a protective effect of firearm regulation that extends across state lines,” Kaufman says.

Strong state firearm laws were also associated with lower rates of suicide deaths from guns and lower overall suicide rates, regardless of neighboring states’ laws. However, it’s unclear which policies were most associated with lower suicide rates. “Our study did not differentiate between individual laws,” Kaufman says, noting that further research could explore which policies influence suicide rates. Counties with lax state firearm laws experienced the highest rates of firearm suicide; the policies of neighboring states had little influence.

Kaufman says the timing of publication had everything to do with the academic review process and wasn’t influenced by the timing of the national debate on gun regulation, but her findings do add to a body of research which suggests that stricter gun regulations can reduce gun deaths. Last year, Donohue wrote an analysis of right-to-carry laws using data from 1977 to 2014. He found that, ten years after a state passed right-to-carry, its rates of violent crime rose between 13 to 15 percent.

The fact that states and counties can influence their own firearm homicide and suicide rates with regulation indicates that the same could be done on the federal level, says UCLA School of Law professor and firearms law expert Adam Winkler. “The study is really an argument both encouraging states to pass laws they think are necessary because they can work even with porous borders,” he says. “And it’s a call for federal laws, because we really need national uniformity to achieve those goals.”

The issue of porous borders is difficult to research because firearms can and do traverse county and state lines without proper documentation, thanks to illegal sales and private sales—such as gun show and online sales—which don’t require background checks in some states. “For this study, we did not directly assess how firearms might move across state lines,” Kaufman says. “We did find that counties in states with lenient laws that were also surrounded by states with lenient laws had the highest firearm death rates; we do not know if firearms are moving legally or illegally.”

In the wake of the Parkland, Florida, school shooting, President Donald Trump has opposed the NRA in suggesting universal background checks for firearms purchases. Both Donohue and Winkler agree that President Trump is in a unique position to change the law. “Only a Republican president can get gun control laws enacted; no Democrat can do that,” Winkler says. “No other Republican president is going to support gun control, and no Democrat would have the political support to get it done.” (Having a congressional majority always helps.)

Donohue, who has decades of experience in gun violence research, says he has no idea whether research like Kaufman’s and shootings like Parkland will influence gun policy. “Trump has oddly shaken up the NRA by saying he’s concerned about this, which is a surprise to everyone,” he says. “It’s also possible that [NRA CEO] Wayne LaPierre will call him up tomorrow and say, ‘When we say jump, you say how high.’”

Tonic spoke with Donohue on the afternoon of Thursday, March 1. Later that night, the New York Times reported that a top NRA lobbyist indicated President Trump had walked back his support for comprehensive gun control following a meeting with NRA officials.

As Robert Steinbrook, the editor at large of JAMA Internal Medicine, wrote in an editor’s note: “Because Congress has been unwilling or unable to act, the need for effective state firearm laws and policies in the United States has never been greater.”