In the United States, a right-to-carry law (sometimes abbreviated RTC law, also known as a shall-issue law) is one that requires that governments issue concealed carry handgun permits to any applicant who meets the necessary criteria. These criteria are: the applicant must be an adult, have no significant criminal record, and no history of mental illness, and successfully complete a course in firearms safety training (if required by law).
Effects
In 1997, John Lott and David Mustard published an influential study analyzing data from all 3,054 United States counties in The Journal of Legal Studies. The study concluded that right-to-carry laws deterred violent crime, "without increasing accidental deaths". In the study, Lott and Mustard also stated that right-to-carry concealed handgun laws were "the most cost-effective method of reducing crime thus far analyzed by economists." The following year another study was published in the same journal which re-analyzed Lott and Mustard's data and concluded that there was "no basis for drawing confident conclusions about the impact of right-to-carry laws on violent crime." Also that year, a study in the American Economic Review found that the effects of concealed handgun laws on crime rates were much smaller than estimated by Lott and Mustard, and that these effects were not negative with respect to all types of crime. For example, the study found that such laws reduced murder only by, at most, a small amount, and that many states' robbery rates increased after these laws were passed. A 2003 study found that the Lott and Mustard study inappropriately used a dummy variable, leading to misspecification, and, based on a different method of analysis, concluded that the effects of these laws varies from county to county and from state to state and "are not crime-reducing in most cases".
A 2002 study found no evidence that right-to-carry laws either increased or decreased the number of mass shootings.
Another study, published in 2001, found that right-to-carry laws "appear to have statistically significant deterrent effects on the numbers of reported murders, rapes, and robberies." In 2004, a report by the National Research Council concluded that there was insufficient evidence to conclude whether there was a cause-and-effect relationship between RTC laws and crime rates. A 2005 study, looking at every American city with a population of at least 100,000 in 1990, found no evidence that these laws affected violent crime rates either. A 2011 study concluded that the most consistent finding from analyses conducted over the 1977-2006 period was that after RTC laws are adopted, aggravated assault increases, though the researchers noted even this finding was not uniform.