During Thursday's debate, Republican frontrunner Donald Trump said that the answer to America's gun problem is, well, more guns: "I am a Second Amendment person. If we had guns in California on the other side where the bullets went in the different direction, you wouldn't have 14 or 15 people dead right now. If even in Paris, if they had guns on the other side going in the opposite direction, you wouldn't have 130 people plus dead."
Trump was articulating the "good guy with a gun" myth: the idea that the answer to shootings — like those in San Bernardino, California, and Paris — is having more people with guns to stop violent perpetrators.
But the research clearly shows that Trump is wrong. Time and time again, the empirical research has found that more guns lead to more gun deaths, and that the US's easy access to guns in fact contributes to gun homicides.
More guns mean more gun deaths
The theory behind the mantra of "a good guy with a gun" is that more people should be armed so they can be ready to defend themselves and others from an active shooter.
But the research suggests that's plainly false: When there are more guns and gun owners, there are far more gun deaths. Studies have found this to be true again and again — for homicides, suicides, domestic violence, and violence against police.
Here's one chart, from a 2007 study by Harvard School of Public Health researchers, showing the correlation between statewide firearm homicide victimization rates and household gun ownership after controlling for robbery rates:
A more recent study from 2013, led by a Boston University School of Public Health researcher, reached similar conclusions: After controlling for multiple variables, the study found that a 1 percent increase in gun ownership correlated with a roughly 0.9 percent rise in the firearm homicide rate at the state level.
This holds up around the world. As Vox's Zack Beauchamp explained, a breakthrough analysis in the 1990s by UC Berkeley's Franklin Zimring and Gordon Hawkins found that the US does not, contrary to the old conventional wisdom, have more crime in general than other Western industrial nations. Instead, the US appears to have more lethal violence — and that's driven in large part by the prevalence of guns.
"A series of specific comparisons of the death rates from property crime and assault in New York City and London show how enormous differences in death risk can be explained even while general patterns are similar," Zimring and Hawkins wrote. "A preference for crimes of personal force and the willingness and ability to use guns in robbery make similar levels of property crime 54 times as deadly in New York City as in London."
THE US APPEARS TO HAVE MORE LETHAL VIOLENCE — AND THAT'S DRIVEN IN LARGE PART BY THE PREVALENCE OF GUNS
This is, in many ways, intuitive: The prevalence of guns can cause petty arguments and conflicts to escalate into deadly encounters. People of every country get into arguments and fights with friends, family, and peers. But in the US, it's much more likely that someone will get angry during an argument, pull out a gun, and kill someone.
These three studies aren't the only ones to reach similar conclusions. Multiple reviews of the research, including the Harvard Injury Control Research Center's aggregation of the evidence, have consistently found a correlation between gun ownership and gun deaths after controlling for other factors.
So chances are a good guy with a gun will not stop a bad guy with a gun. In fact, trying to produce more good guys with guns could make gun deaths far, far more frequent.