States with weaker concealed carry laws are associated with significantly higher rates of handgun homicide, according to a study published in the American Journal of Public Health on Thursday.

The findings are the latest volley in the decades-old debate over whether arming citizens makes the public safer or increases violent crime, and they come while the National Rifle Association is pushing for legislation that would loosen safety standards on concealed carry all across the country.

Every state allows the carrying of concealed firearms under some circumstances, but the permitting process varies by jurisdiction. In some states, law enforcement can deny a permit if they believe the applicant lacks good character, or doesn’t have a good reason to carry a loaded gun in public. In other states, they are essentially required to issue a permit to anyone who meets certain statutory requirements. A growing number of states don’t require a permit at all.

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Researchers from the Boston University School of Public Health compared homicide rates from 1991 to 2015 in states where law enforcement has wide discretion to reject concealed carry permits, which they call “may-issue” states, with those of states in which permits must be issued if an individual meets the necessary criteria, referred to as “shall-issue” or “right-to-carry” states.

They found that shall-issue states were associated with 8.6 percent higher firearm homicide rates and 10.6 percent higher handgun homicide rates. The study suggests that allowing law enforcement the discretion to reject applicants may save lives.

“If these findings are accurate, we are really moving in the wrong direction by making it easier for people to carry concealed weapons,” said Michael Siegel, professor of community health sciences at the Boston University School of Public Health and the study’s senior author.

In some shall-issue states, a person can get a permit even if they have convictions for violent misdemeanors or were previously subject to a domestic violence restraining order. But if that same person resided in a may-issue state, Siegel explained, law enforcement could consider their history of red flags before approving them to carry a loaded gun in public.

“Just having a list of criteria is not enough ― especially if those criteria are not as stringent and only cover felonies,” he said.

The research coincides with the National Rifle Association’s lobbying efforts to pass federal legislation dubbed “national concealed carry reciprocity,” which would allow individuals to carry a gun in any state ― as long as they have a concealed carry permit in their home state. In January, Rep. Richard Hudson (R-N.C.) introduced the Concealed Carry Reciprocity Act. Sen. John Cornyn (R-Texas) introduced a similar bill in the Senate.

“Our research suggests that these laws would actually represent a threat to public safety,” Siegel said. “It would force states to allow people to carry concealed weapons who normally, under that state law, may not have access to one.”

Sen. Chuck Schumer (D-N.Y.), who criticized the NRA for pushing the concealed carry bill just days after a mass shooting in Las Vegas, said the new research “debunks the NRA’s false narrative” that lax gun laws make Americans safer.

“The study’s conclusions are crystal clear: The last thing we, as federal lawmakers, should do is support a dangerous national conceal carry law that could increase violence when our job is to pass laws to keep our communities safe,” he said.

Gun violence prevention advocates say national concealed carry reciprocity would turn states with the most permissive standards into the law of the land, and would erode states’ rights to protect their own residents.

But proponents argue that permits should be treated like driver’s licenses. If you have one in one state, it should be recognized everywhere else.

Daniel Webster, director of the Johns Hopkins Center for Gun Policy & Research, dismissed that analogy as absurd. The process of getting a license is fairly uniform across the U.S., he explained.

“You have a vision test, you have a driving test, and you have to demonstrate you know the laws,” he said. But the permitting process for concealed carry depends entirely on where a person is living.

“In the vast majority of states that issue permits, there is no such vetting to demonstrate that you can safely carry a concealed, loaded weapon around with you in public,” he said.

For example, only 31 states require individuals to complete some form of safety training before receiving a permit, according to Everytown for Gun Safety. If national concealed carry reciprocity passed, a person could get a permit in a state where safety training was not mandated, then carry it into a state with far more stringent requirements.

Webster also pushed back on the NRA’s talking point that concealed carry makes the country safer. On its website, the NRA implies that part of the reason the violent crime rate has plummeted since 1991 is because 25 states adopted right-to-carry laws, and more people are carrying concealed weapons. According to the Crime Prevention Research Center, there are over 16.3 million permit holders in the U.S.

Every state saw a substantial reduction in violent crime during the ’90s, Webster said, including right-to-carry states. “But what would have happened if they had not passed right-to-carry?” he asked. “We see even sharper declines in states that did not adopt those laws.”

The NRA did not respond to a request for comment.

Jonas Oransky, deputy legal director at Everytown for Gun Safety, said he has seen a significant loosening of concealed carry laws in recent years. Since 2014, eight states have repealed their permit requirements altogether, bringing the total number of states allowing people to carry without any permit whatsoever to 12.

“Concealed carry reciprocity would be the worst possible outcome for concealed carry laws ― gutting state gun laws and forcing all states to live with the most dangerous systems,” he said.

He called Boston University’s research one of two landmark studies this year on the issue, pointing also to a working paper published in June by John Donohue, a professor at Stanford Law School. It found states that adopted right-to-carry laws experienced a 13 to 15 percent increase in violent crime in the 10 years after enacting those laws.

When asked about the Boston University study, Donohue said he was not surprised by the results, as they aligned with his earlier work ― but they worried him.

“If you are in one of the states that doesn’t have right-to-carry, you should probably be calling your senator or congressmen right now to stop this new initiative,” he said of concealed carry reciprocity.

“All it will do is extend the pain,” he continued. “It’s a bad idea with respect to saving lives.”