[2][3] Gun Violence Archive, a nonprofit research group that tracks shootings and their characteristics in the United States, defines a mass shooting as an incident in which four or more people, excluding the perpetrator(s), are shot in one location at roughly the same time.
[4] The Congressional Research Service narrows that definition to four or more killed and excludes the injured who survive.
[6][7] The crowdsourced Mass Shooting Tracker project applies the most expansive definition: four or more shot in any incident, including the perpetrator.
[8][9] A 2019 study of mass shootings published in the journal Injury Epidemiology recommended developing "a standard definition that considers both fatalities and nonfatalities to most appropriately convey the burden of mass shootings on gun violence.
"[10] The authors of the study further suggested that "the definition of mass shooting should be four or more people, excluding the shooter, who are shot in a single event regardless of the motive, setting or number of deaths.