Now I Get It: U.S. mass shootings compared with the rest of the world

On Wednesday, at least 17 people were killed and dozens injured when a gunman opened fire on Marjory Stoneman Douglas High School in Parkland, Fla. So far in 2018, there have been 17 other instances when a gun was fired on or near a U.S. school, including six incidents in which students were either killed or injured. A study by the University of Alabama's Adam Lankford says the U.S. has the most public mass shootings than any other country in the world. Why is that?