With 5% of world's population, U.S. had 31% of the world’s public mass shooters in 1966-2012

“Given the fact that the United States has over 200 million more firearms in circulation than any other country, it’s not surprising that our public mass shooters would be more likely to arm themselves with multiple weapons than foreign offenders,” Lankford said. “I was surprised, however, that the average number of victims killed by each shooter was actually higher in other countries (8.81 victims) than it was in the United States (6.87 victims) because so many horrific attacks have occurred here.”

The side-effect of America having experienced so many mass shootings may be that our police are better trained to respond to these incidents than law enforcement in other countries, which reduces the number of casualties, Lankford suggested.

The ASA notes that in addition to killing fewer people and using more weapons, U.S. public mass shooters were also more likely to attack in schools, factories/warehouses, and office buildings than offenders in other countries. Compared to U.S. shooters, however, attackers abroad were significantly more likely to strike in military settings, such as bases, barracks, and checkpoints.

While Lankford’s study revealed a strong link between the civilian firearm ownership rate and the large number of public mass shooters in the United States, he said there could be other factors that make the United States especially prone to public mass shooting incidents.

“In the United States, where many individuals are socialized to assume that they will reach great levels of success and achieve ‘the American Dream,’ there may be particularly high levels of strain among those who encounter blocked goals or have negative social interactions with their peers, coworkers, or bosses,” Lankford explained. “When we add depression, schizophrenia, paranoia, or narcissism into the mix, this could explain why the United States has such a disproportionate number of public mass shooters. Other countries certainly have their share of people who struggle with these problems, but they may be less likely to indulge in the delusions of grandeur that are common among these offenders in the United States, and, of course, less likely to get their hands on the guns necessary for such attacks.”

In terms of the study’s policy implications, Lankford said, “The most obvious implication is that the United States could likely reduce its number of school shootings, workplace shootings, and public mass shootings in other places if it reduced the number of guns in circulation.”

There is evidence that such an approach could be successful, according to Lankford. “From 1987 to 1996, four public mass shootings occurred in Australia,” Lankford said. “Just twelve days after a mass shooter killed thirty-five people in the last of these attacks, Australia agreed to pass comprehensive gun control laws. It also launched a major buyback program that reduced Australia’s total number of firearms by 20 percent. My study shows that in the wake of these policies, Australia has yet to experience another public mass shooting.”