The definition of a mass shooting remains under debate. The precise inclusion criteria are disputed, and there no broadly accepted definition exists. Mother Jones, using their standard of a mass shooting where a lone gunman kills at least four people in a public place for motivations excluding gang violence or robbery, concluded that between 1982 and 2006 there were 40 mass shootings (an average of 1.6 per year). More recently, from 2007 through May 2018, there have been 61 mass shootings (an average of 5.4 per year). More broadly, the frequency of mass shootings steadily declined throughout the 1990s and early 2000s, then increased dramatically.
