Or we could use the FBI’s definition of a mass shooting: one in which at least four people, not including the perpetrator, are killed. This is a vastly larger category than the one Maddow employs: there were about 600 such incidents in the United States between 1980 and 2010.  As James Alan Fox, a professor of criminology at Northeastern University points out, the rate of such mass shootings does not appear to be rising.