As a country, the United States comprises 5 percent of the global population, but has experienced 31 percent of public mass shootings across the world between 1966 and 2012, according to new research.

This disproportionate number of mass killings is likely linked to civilian rates of gun ownership.

“The United States, Yemen, Switzerland, Finland and Serbia are ranked as the Top 5 countries in firearms owned per capita, according to the 2007 Small Arms Survey,” said study author Adam Lankford in a statement. “And my study found that all five are ranked in the Top 15 countries in public mass shooters per capita. That is not a coincidence.”

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At the same time, cultural and social factors unique to the United States might also play a role, said Lankford, who mined data from the NYPD, the FBI and multiple international sources to create the first qualitative analysis of public mass shootings that ended in four or more deaths.

“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,” he said.

Mental illnesses like paranoia, schizophrenia and narcissism may compound the problem,  Lankford said -- and though people in other countries wrestle with the same issues “they may be less likely to indulge in the delusions of grandeur that are common among these offenders in the U.S.”

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An unexpected discovery? Mass shooters in the United States kill fewer people, on average, than shooters in other countries.

This finding seems counterintuitive, but it might be a direct result of having been home to so many large-scale gun massacres: The police in the United States are better trained to respond to mass shootings because there have been so many of them, Lankford said.