With three of the 10 most deadly mass shootings in US history coming in the last five months, Americans are clearly energized about this growing problem that disproportionately plagues the United States. While there are many steps that are widely popular, such as adopting improved, universal background checks, which could be expected to reduce all mass shootings and much other crime, President Trump has instead focused on the controversial suggestion of arming teachers to prevent school shootings. Unfortunately, this discussion is not being informed by the existing data on both mass shootings and what terminates them or the general information on the impact of increased gun carrying on violent crime.

The FBI analyzed 160 cases of active shooters over the period from 2000-2013, and not one was stopped by a concealed carry permit holder who was not active duty military, a security guard, or a police officer. 21 were stopped by unarmed civilians.

The President’s remarks also conveyed a sense that with an armed teacher around, any shooter would quickly be shot and killed, ending the potential tragedy quickly and happily. The real world has not been so neat. There was an armed law enforcement officer present at the time of the 1999 school shooting in Columbine who did engage in a gun battle with the killers but this did not quickly and easily stop the assault. In fact, twelve police officers fired 141 shots at the two killers, none of which hit their targets. Overall, 12 students and one teacher died, and 21 were injured before the two killers committed suicide.

The FBI report also shows that firing on active duty shooters is also a dangerous enterprise: in 21 of the 45 cases in which police exchanged gun fire, an officer either died (9 officers) or was shot (28 officers). The data from a large array of studies shows that trained police play a critical role in reducing crime, but it is important to note that in active shooter incidents they confront very significant dangers.

The President did indicate that he was not in favor of allowing any teacher with a concealed carry permit to have a gun in school but was referring to more skilled and trained individuals. This is an important point since the evidence for the average concealed carry individual is that he or she will not be of much help in a mass shooting incident and tends to elevate the risk of violent crime in general. Again, the existing debate does not seem well-informed by the full complexities of increasing the carrying of concealed weapons.

The best empirical evidence suggests that when states adopt right to carry laws, violent crime tends to rise by about 13-15 percent over the next ten years, so the general notion that arming law-abiding citizens to carry guns outside the home will improve safety has no statistical support. There are certainly beneficial uses of guns by permit holders that thwart or even deter crime, but these positive influences are outweighed by all of the ways—often not well understood—in which gun carrying elevates violent crime. In addition to any misconduct by the actual permit holder—such as the mass shooting in 2017 that killed five and wounded six others in the baggage claim area at the Fort Lauderdale-Hollywood Airport—gun carrying often leads to lost and stolen guns and occupies the time and complicates the task of law enforcement in ways that undermine their crime-fighting capacities.

I estimate that roughly 100,000 guns are stolen from concealed carry permit holders each year so any good they do has to be offset by the arming of 100,000 criminals and the violent crimes these armed criminals commit. If Trump’s plan were to lead to five armed teachers per school in the roughly 100,000 elementary and secondary schools, this would mean that 500,000 teachers would be bearing arms in school every school day. If they experienced a similar rate of lost and stolen guns as concealed carriers in general, that would suggest they would relinquish roughly 5000 guns per year, which is a threat to the entire community. It also suggests that should the Trump plan be adopted, it would be wise to insist that the only guns that teachers could bring to school would be smart guns that could only be fired by the permit holder, as opposed to some unauthorized individual.

Striving to keep guns away from identifiably dangerous individuals through an enhanced and universal background check system and limiting the destructive potential of their weaponry are likely to be critical components of any effective plan designed to reduce gun violence and mass shootings.