In a recent paper, Stanford law professor John Donohue found that states that adopted right-to-carry (RTC) concealed handgun laws were reported to have a 13 to 15 percent higher crime rate over a period of 10 years than states that opted to not adopt those laws.

Donohue worked with Stanford research fellows Abhay Aneja and Kyle D. Weber on the paper, which is titled “Right-to-Carry Laws and Violent Crime: A Comprehensive Assessment Using Panel Data and a State-Level Synthetic Controls Analysis.” The paper is based on his study of a 2004 report of the National Research Council on Firearms and Violence. This report originally proved that violent crime was higher after the passage of RTC laws; however, the experts on the panel were ultimately unable to conclude that the sole act of carrying weapons had an impact on violent crime.

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

Donohue then applied the synthetic control approach to four other statistical models: the DAW model, the Brennan Center model, the Lott and Mustard (LM) model and the Moody and Marvell (MM) model. According to the paper, in all four cases, RTC laws were shown to increase overall violent crime when allowed to run with the most complete sets of data.

However, with the increase of violent crimes comes the concern of incarceration rates. Donohue noticed an upward trend amongst RTC states and incarceration rates–not only were incarceration rates higher, but the hiring of law enforcement personnel was also greater. Donohue found that “the average RTC state would have to double its prison population to counteract the RTC-induced increase in violent crime.”

“RTC states were not simply experiencing higher crime because they decided to lock up fewer criminals and hire fewer police,” he said to Stanford News. “Our synthetic controls estimates may be understating the increase in violent crime.”