While the National Rifle Association (NRA) has long insisted that allowing Americans to carry guns make communities safer, an analysis of nearly 40 years’ worth of data has found that is not necessarily true.

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A Stanford Law School professor, John Donohue, and his team analyzed crime data from 1977 to 2014 and didn’t find evidence that areas where more Americans carry guns enjoy enhanced public safety or less crime. On the contrary, the researchers discovered that states that have enacted so-called right-to-carry (RTC) concealed handgun laws have experienced higher rates of violent crime than states that did not adopt those laws.

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“There is not even the slightest hint in the data that RTC laws reduce overall violent crime,” Donohue said.

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Donohue’s paper revisits a 2004 study published by the National Research Council on Firearms and Violence that did not reach a definitive conclusion about the effect of “shall issue” laws on violent crime, saying there was insufficient data. Other studies conducted since 1994 have undermined the gun-rights movement theory, which The Trace reports was first posited by economist John Lott in a 1998 book, More Guns, Less Crime. The site calls the new report the most comprehensive and assertive debunking of the theory.

“All this work is based on statistical models,” Donohue said. “When the models all generate similar estimates, it increases your confidence that you have captured the true effect.”

Donohue’s paper has been included in court filings in federal district court in a case involving the NRA and California, according to Stanford. The gun group is suing the state over its gun laws, which are some of the strictest in the U.S. For six years since 2010, the Law Center to Prevent Gun Violence has ranked it No. 1 for strongest firearms legislation in the country.