How do different organizations define a mass shooting and how do counts vary?
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Executive summary
Different organizations use sharply different thresholds and criteria: the Gun Violence Archive (and media that use it) counts incidents with four or more people shot, excluding the shooter (e.g., GVA counted about 381–389 mass shootings in 2025) [1] [2]. Other trackers use fatality-based or public-place tests — the AP/USA Today/Northeastern “mass killings” database counts events with four or more killed [3] [4]. These definitional choices drive large differences in annual counts and which incidents are visible in public debate [5].
1. Why the numbers diverge: victims shot vs. victims killed
Counting “four or more shot” produces many more events than counting “four or more killed.” The Gun Violence Archive’s working definition — any incident in which four or more people are shot, not including the shooter — yields hundreds of incidents per year (GVA had recorded roughly 325–389 mass shootings in 2025 in different snapshots) [1] [2] [6]. By contrast, the AP/USA Today/Northeastern “mass killings” database, which requires four or more fatalities, recorded 17 mass killings in 2025 to date — the lowest in two decades — showing how fatality thresholds compress counts [3] [4].
2. Public place, motive, and “mass public shootings”: narrower academic definitions
Some researchers and institutes restrict the term to targeted violence in public or populated places, excluding domestic or gang incidents. The Rockefeller Institute cites a definition of “an incident of targeted violence … at one or more public or populated locations” and relies on curated academic datasets that cross‑check media reports against a strict public‑place standard [7]. Mother Jones and some academic datasets adopt similarly narrow, often fatality‑based criteria; Mother Jones has described its approach as a “conservative measure” that excludes many shootings with fewer deaths [8].
3. Crowd‑sourced and real‑time trackers broaden the picture
Crowd-sourced projects such as the Mass Shooting Tracker define a mass shooting as a single outburst in which four or more people are shot, producing tallies more aligned with GVA [9]. These projects prioritize near-real-time capture and broader inclusion — including domestic gatherings, gang incidents and nonfatal events — which surfaces a different pattern of gun violence than fatality‑only lists [1] [9].
4. The policy and narrative impact of definitional choices
Which definition a news outlet or policymaker uses shapes public perception and policy focus. Fatality‑based databases emphasize the deadliest incidents and may highlight public‑space rampages, which drive national policy debates; shot‑victim counts emphasize the wider burden of gun violence including mass injuries and family‑based incidents [4] [5]. Journalists and advocates commonly use GVA counts to show scope; researchers relying on strict “mass killing” definitions argue those numbers better measure the rarest, most catastrophic events [2] [3].
5. Year‑to‑year volatility and “regression to the mean”
Because some definitions capture only a few dozen events (fatality‑based mass killings), year‑to‑year totals are highly volatile; experts warn a small change can look like a long‑term trend when it is statistical noise. Analysts told PBS and The Guardian that 2025’s drop in mass killings is likely a return to average after spikes in 2018–2019 rather than a permanent change [10] [11]. GVA and other broader trackers also reported declines in 2025, but absolute counts remain much higher under their criteria [6] [12].
6. What gets excluded or hidden by each approach
Narrow public‑place or fatality‑only definitions exclude many incidents that cause trauma, injuries, and community harm: domestic mass shootings, many school‑adjacent incidents with nonfatal injuries, and events where rapid medical care reduced deaths [8] [13] [14]. Available sources do not mention a single universally accepted legal definition of “mass shooting” in the U.S.; they state instead that “there is no generally accepted definition” and that researchers recommend a standard that includes both fatalities and nonfatalities [8] [8].
7. Practical guidance for readers and reporters
When you see a headline about “mass shootings,” ask which definition is being used: four or more shot (GVA/Mass Shooting Tracker), four or more killed (AP/USA Today/Northeastern), or a public‑place/fatality threshold (Rockefeller/Mother Jones/academic datasets) [1] [3] [7] [8]. Different definitions highlight different policy problems — public rampage prevention vs. broader gun‑violence reduction — and each comes with implicit agendas: narrower definitions concentrate attention on high‑fatality public attacks; broader definitions emphasize the everyday scale of firearm injuries and community impact [4] [12].
Limitations: this account uses the provided sources; available sources do not mention any single, legally binding federal definition of “mass shooting” [15] [8].