Right-to-carry handgun laws trigger a 13% to 15% increase in violent crime a decade after the typical state adopts them, suggests a new statistical analysis of 33 US states.

The Journal of Empirical Legal Studies report released Monday is the latest in a thorny academic fight over how letting people more freely carry around guns affects those crimes.

Advocacy for and against looser gun laws will doubtless grow louder as the US Supreme Court is expected to hear a challenge to a ban on taking a licensed handgun outside New York City limits without a permit, its first gun control case in nearly a decade. The court, split along partisan lines 5–4 in favor of judges who have previously favored expanded gun rights, could decide that there is a constitutional right to carry a gun outside the home.

But that could be “a dangerous mistake to make,” according to the new study’s lead author, Stanford Law School’s John Donohue.

“The important takeaway is that more guns seems to lead to more crime,” Donohue told BuzzFeed News by email. “So it is probably wise to think in terms of appropriate controls and it would be very unwise to push the 2nd Amendment too far.”

This long-running and contentious statistical debate began with the 1998 book More Guns, Less Crime by John Lott Jr. of the Crime Prevention Research Center. Since its publication, 11 states have loosened right-to-carry laws, and more than 30 states now allow the open carrying of a gun without a permit.

About 3.1 million people in the US were victims of violent crimes, rapes, robberies, and assaults in 2017, according to the Bureau of Justice Statistics. In the new study, statisticians looked at right-to-carry law effects on those numbers by adding data from the 11 states that have adopted them in the last 15 years to create a record of 33 states that allowed citizens to carry concealed weapons from 1981 to 2007.

The team looked at violent crime rates in all of the states, controlling statistically for the effects of policing, incarceration rates, poverty, and other demographic trends to estimate the changes caused by the right-to-carry laws.

“It was really only after we had 14 more years of data and 11 additional adoptions of RTC laws that a clear picture emerged that RTC laws increase violent crime,” Donahue said.

For 23 of the 31 states adopting the laws, the increase in violent crime was large, for example, in Pennsylvania up by more than 24% in 10 years, and up by nearly 17% in Texas. In South Dakota, the results suggest a right-to-carry law led to a 1.6% drop in violent crime rates after a decade.

To jail all the people committing these added violent crimes, the average state would need to double its prison population, the analysis concludes. The study cataloged recent road rage disputes, bar fights, police shootings of armed civilians, and everyday vitriol that turned into shootings in right-to-carry states, to suggest mechanisms that explain how the increases might happen. The study didn’t find a statistically significant change in the rates of homicides or property crimes.

A number of crime scholars contacted by BuzzFeed News praised the finding as the most complete accounting yet for the violent crime effects of letting more people carry around guns.

“I have read the study and consider it to be the most rigorous of studies of right-to-carry laws to date,” Daniel Webster, director of the Center for Gun Policy and Research at the Johns Hopkins Bloomberg School of Public Health, wrote to BuzzFeed News in an email. Given state legislative and federal court battles over these laws, he said, “this is a very important piece of research.”

The More Guns, Less Crime estimate in the ’90s didn’t factor in the levels of police and imprisonment in each state, which the new study found grew significantly after the passage of right-to-carry laws, and helps explain their disagreeing conclusions.

Lott, however, was strongly dismissive of the study, arguing that the bulk of reports over the last two decades have supported his findings, or found no effect on violent crime rates. “Basically, poor areas are more likely to be affected by violent crime, so lowering barriers to permits has a bigger effect in states that do so,” Lott told BuzzFeed News, an effect he said the new study didn’t account for.

He complained that more right-to-carry studies than his, finding no effect or reduced crime rates, “have gotten no news coverage.”

However, Duke University criminologist Philip Cook told BuzzFeed News that a new study with better methods and data toppling an old, incorrect theory is just an example of how science works.

“The scientific process does not always get the right answer the first time, but if it’s working well, then important findings are reviewed and tested and the truth becomes clearer,” said Cook, in the case of the newer, better study of 33 states. Regardless, he added, advocates for the “more guns, less crime” idea will likely continue beating the drum for right-to-carry laws.