When the world looks at the United States they are puzzled by the many mass shootings. Some speculate that American society is unusually violent. Or its racial divisions have frayed the bonds of society. Or its citizens lack proper mental care under a health care system that draws frequent derision abroad.
Americans make up about 4.4% of the global population but own 42% of the world's guns. From 1966 to 2012, 31% of the gunmen in mass shoots worldwide were American, according to a 2015 study by a professor at the University of Alabama.
Adjusted for population, only Yemen has a higher rate of mass shootings among countries with more than 10 million people. Yemen has the world's second-highest rate of gun ownership after the United States.
If mental health made the difference, the data would show that Americans have more mental health problems than people in other countries with fewer mass shootings.