What are the definitions of mass shooting used by the FBI, Gun Violence Archive, and CDC?
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Executive summary
Different agencies and databases use distinct thresholds and concepts: the FBI reports on “active shooter incidents” — “one or more individuals actively engaged in killing or attempting to kill people in a populated area” — and applies the separate federal “mass killing” threshold of four or more people killed in some reports [1] [2]. The Gun Violence Archive (GVA) defines a “mass shooting” as an incident in which a minimum of four victims are shot (injured or killed), excluding the shooter [3] [4]. The CDC does not publish a single, standalone public definition called “mass shooting” in these sources; its data on firearm deaths are based on death certificates and different surveillance systems (available sources do not mention a CDC definition of “mass shooting”; p1_s7).
1. FBI: “Active shooter” language, and a four-or-more fatalities legacy
The FBI frames the problem as “active shooter incidents,” defining an active shooter as “one or more individuals actively engaged in killing or attempting to kill people in a populated area,” language the bureau uses in its public reports and tallying [1] [5]. Historically, law-enforcement and federal reporting have also used the related term “mass killing” — often defined as four or more killed — and some FBI analyses apply that four-or-more fatalities threshold when identifying “mass” incidents for certain historical or analytical purposes [2] [6]. The bureau’s operational focus on shootings in-progress and mass killings means its counts can be narrower than groups that count nonfatal victims [1] [2].
2. Gun Violence Archive: four-or-more shot (injured or killed), inclusionary approach
Gun Violence Archive defines a mass shooting as any single incident in which at least four people are shot — either injured or killed — not including the shooter [3] [4]. GVA emphasizes a purely numeric threshold and intentionally includes all settings and motives (domestic disputes, robberies, accidental shootings, public rampage events), explaining that it uses a fully inclusionary approach and does not exclude subcategories of shootings [4]. That methodology produces far larger counts than sources that require four fatalities or restrict to public, indiscriminate attacks [7] [8].
3. CDC: data source and surveillance role, not a standalone “mass shooting” definition in available sources
The sources provided describe the CDC’s role in collecting mortality data from death certificates and in public-health surveillance, but they do not present a single CDC definition of “mass shooting” [1]. Reporting contrasts CDC death-certificate–based statistics with FBI data drawn from voluntary law-enforcement submissions, underscoring that the CDC’s counting system measures deaths rather than a discrete “mass shooting” category [1]. Available sources do not mention a CDC definition of “mass shooting” (available sources do not mention a CDC definition of “mass shooting”; p1_s7).
4. Why definitions matter: tallies, trends and public perception
Differences in definitions produce dramatically different totals and narratives: using a four-or-more-killed threshold yields far fewer incidents than counting events with four or more people shot, and counting only “active shooter” public incidents narrows the scope further [6] [3]. Analyses and media relying on GVA’s inclusive threshold will report many more “mass shootings” than FBI reports that center on active shooters or federal “mass killing” criteria [7] [2]. Researchers and policymakers warn that the lack of a uniform federal definition complicates trend analysis and policy evaluation [9] [2].
5. Competing agendas and methodological trade-offs
Each approach reflects an implicit agenda: the FBI’s operational definition prioritizes incidents requiring immediate tactical response and identifies those with the highest lethality [1] [2]. GVA’s inclusive numeric rule prioritizes comprehensiveness and near-real-time public tracking at the cost of aggregating very different incident types into a single bucket [4] [8]. Public debate often pivots on which framing better serves prevention policy or public awareness; critics argue GVA’s counts inflate “mass shooting” as commonly understood, while proponents say fatality-only measures undercount the societal toll [10] [4].
6. Bottom line for readers and journalists
When you see a published count, check which definition is being used: FBI/“active shooter” language focuses on people actively attempting to kill in public and sometimes uses a four-or-more-killed mass-killing threshold [1] [2]; Gun Violence Archive counts events with four or more people shot, injured or killed [3] [4]; and the CDC provides mortality data from death certificates but does not supply a clear, separate “mass shooting” definition in the cited sources [1]. The divergent definitions drive the different headlines; understanding the metric clarifies what a number actually measures [9] [7].