Examining four decades of crime data, a team of Stanford researchers found that states that have enacted so-called ‘right to carry’ (RTC) concealed handgun laws experience higher rates of violent crime than states where these laws have not been adopted. The findings are among the most powerful evidence in a growing line of research refuting the claim that arming more citizens enhances public safety.

“There is not even the slightest hint in the data that RTC laws reduce overall violent crime,” Stanford Law Professor John Donohue and colleagues concluded in the new study.

RTC laws, also known as ‘shall issue’ laws, lower the bar to qualify for a concealed carry license by requiring states to issue concealed-carry permits to anyone who meets basic criteria for gun ownership. As a result, states that adopt RTC laws grant concealed carry permits at higher rates than states where more discretion is used (“may issue” states) and thus have greater numbers of armed citizens.

If, as groups like the National Rifle Association argue, higher rates of gun ownership really do reduce crime, we would expect to see lower crime rates in states with RTC laws, where more residents carry guns. But that’s not what the evidence shows. In fact, as this latest study found, the evidence suggests that just the opposite is true.

“We estimate that the adoption of RTC laws substantially elevates violent crime rates,” the Stanford researchers concluded in a working paper published by the National Bureau of Economic Research. “Ten years after the adoption of RTC laws, violent crime [in RTC states] is estimated to be 13–15 percent higher than it would have been without the RTC law.”

The analysis builds on a 2004 NBER report, which debunked claims that RTC laws were associated with less crime, but was not able to definitively conclude that concealed carry rates influenced violent crime rates — in either direction. At the time, researchers were limited by uncertainty in the estimates produced by the best available data and statistical models.

“The committee found that answers to some of the most pressing questions cannot be addressed with existing data and research methods, however well designed,” the 2004 report stated.

Synthetic States

To overcome the limitations in the initial report, the Stanford researchers used a new statistical method that estimates what crime rates would have looked like in RTC states had they not adopted RTC laws, accounting for differences across other explanatory variables such as demographic changes, economic factors, and policing practices.

To do this, the team built artificial, or “synthetic,” states to serve as near-identical counterparts to the 33 states that passed RTC laws between 1981 and 2014. Using state-level crime rates prior to the laws’ adoption, as well as national crime data from before and after, the researchers created an algorithm to predict what crime trends would have looked like had these areas never passed RTC laws. Then, they compared crime rates in the actual states with findings from the model using the synthetic control states, repeating the analysis for all 33 RTC states.

The results were strikingly consistent: After applying the synthetic control approach to four previously published statistical data models, the researchers found that in all four cases, RTC states experienced a 13–15 percent increase in violent crime rates within 10 years of the law’s passage.

“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.”

The study also found that although nationwide violent crime rates have fallen as right-to-carry laws have proliferated, the drop was not evenly distributed: In those states that didn’t adopt RTC laws, the decrease in violent crime was four times greater than in states that did enact these laws.

While violent crime rates fell nationwide as many states adopted right-to-carry (RTC) laws, the drop was four times greater in states that did not enact RTC — another piece of evidence showing that more people carrying guns does not deter violent crime.

These findings are particularly notable given that RTC states were found to have increased rates of incarceration and hiring of law enforcement personnel — factors that would usually be associated with less violent crime, not more.

“This suggested that RTC states were not simply experiencing higher crime because they decided to lock up fewer criminals and hire fewer police,” Donohue said. “The relatively greater increases in incarceration and police in RTC states implies that, if anything, our synthetic controls estimates may be understating the increase in violent crime, which was pretty persuasive to me.”

This study is consistent with other recent analyses examining the relationship between gun laws and violent crime rates. In one of most comprehensive studies in the field, researchers determined that gun ownership is the main factor driving gun violence trends in the United States. “For each percentage point increase in gun ownership the firearm homicide rate increased by 0.9 percent,” the study concluded. This relationship has also been documented on a global scale, with a country’s gun ownership rate emerging as a strong and independent predictor of their firearm homicide rate.

Concealed Carry: Weighing the Risks

Donohue acknowledges that under certain circumstances, carrying a gun may confer benefits. For example, many people carry guns for self-defense purposes; with sufficient training, successful defensive firearm uses do occur. However, the overall harm far outweighs the benefits, Donohue said, pointing to a 2013 report that found no evidence of any defensive gun uses in over 99 percent of violent crimes in the U.S. — despite the record number of firearms in circulation in the U.S. today (nearly 300 million).

Donohue’s claim is supported by an expansive body of research showing that guns are far more likely to be used to injure, kill, or threaten than to be used in self-defense. Furthermore, many reported self-defense gun uses are actually aggressive rather than protective in nature. For example, in a pair of nationwide surveys assessing incidents of gun victimization and defensive gun uses, many people reported using guns in situations that did not involve a physical threat in the first place — including verbal altercations, unarmed trespassing, and even minor annoyances like being interrupted while watching a movie. “Guns are used to threaten and intimidate far more often than they are used in self defense,” the study authors concluded. “Most self reported self defense gun uses may well be illegal and against the interests of society.”

For the vast majority of Americans, Donohue said, carrying a gun to avoid becoming a crime victim is akin to thinking that having a weekly brain scan will save your life, without considering the potential hazardous effects of radiation exposure.

“If we gave 300 million people a brain scan, we would save a certain number of lives,” Donohue said. “But you wouldn’t want to advocate that treatment without considering how many lives would be lost by exposing so many to radiation damage. One needs to consider both the costs and benefits of any treatment or policy. If the net effect of more gun carrying is that violent crime is elevated, then RTC laws seem much less appealing.”