The number of shooting incidents resulting in more than four deaths has continued to increase in recent decades.
A 2015 analysis by the Congressional Research Service defined mass public shootings as incidents in which four or more people are killed in one event in a public place such as a workplace, school, restaurant or church. The CRS reported that the number of such incidents had increased steadily in every decade from 1970 to 2013.
The nonprofit Gun Violence Archive uses a broader definition of mass shooting: any incident in which four or more people are killed, excluding the assailant. Their reports have tracked an increase in mass shootings since 2014.
The FBI defines “active shooter” incidents similarly to the CRS, but without a numerical requirement. The agency reports a net increase in such shootings in the period from 2000 through 2018.