The researchers built fictional, or “synthetic,” states as near-identical counterparts to the 33 that passed right-to-carry laws between 1981 and 2014. Using the states’ crime rates prior to the laws’ adoption, as well as national crime data from before and after, they created an algorithm to estimate what trends would have been prevalent had these areas never passed right-to-carry. The researchers then compared crime in the real states with findings from their synthetic versions.

“Ten years after the adoption of RTC laws, violent crime is estimated to be 13 [percent to] 15 percent higher than it would have been without the RTC law,” the authors concluded. Just five years after, it’s about 7 percent higher. “There is not even the slightest hint in the data that [these] laws reduce violent crime,” they write.

I spoke with one of the lead authors, Stanford Law School economist John J. Donohue III—who personally supports stricter gun-control laws—about the report and its implications. Our conversation has been edited for length and clarity.

Maura Ewing: Could I sum up your new study with the phrase “fewer guns, less crime”?

John J. Donohue III: It’s probably too general a statement. But if states are contemplating, “Should we move to the more permissive regime of allowing citizens to carry concealed handguns?” I do think we can say that it’s not a good idea. That will lead to higher levels of violent crime.

Ewing: Why didn’t you focus on states that don’t require a gun permit at all?

Donohue: I could have done that, although it’s a very recent phenomenon that states have moved in that direction. Usually we’d like to have 10 years of data after a [legislative] change gets made. Most of the states that have eliminated permits have done so just in the past couple of years.

Ewing: So you’re specifically tracking the loosening of gun laws, which is the predominant trend among states?

Donohue: Indeed. When John Lott wrote his paper, there were just a handful of states that had adopted these permissive [right-to-carry] laws. Over time, more and more states have moved in that direction. Clearly the trend is in the direction that the National Rifle Association wants.

Ewing: Why was your study necessary? A 2004 National Research Council report essentially debunked Lott and Mustard’s claim that these laws reduce violent crime.

Donohue: It did. I was probably the first one, with various co-authors, to come down hard on the Lott study [in previous papers]. The NRC report essentially adopted all of our criticism on the Lott study, but was much more muted in their expression of what they actually thought the effect of these laws was. The authors essentially said: “There are no statistical supports for the claims that Lott has made, but we are not drawing any inference as to whether they are good or bad or crime goes up or down.” So it was essentially a dismantling, but not an affirmative statement.