Summary
The term "mass shooting" does not have a commonly agreed upon definition, however, in 2013 the FBI began tracking "mass killings", defined by the Investigative Assistance for Violent Crimes Act of 2012 as the killing of three or more people in public spaces. [i] While the Act does not specify, the FBI interprets mass killings as excluding the perpetrator from the three persons killed. The FBI has since published numbers for active shooter events meeting the federal "mass killings" definition for the years 2000 - 2020. These "active shooter mass killing" incidents in the United States (US) increased an average of 12% per year from 2000 to 2020. These 21 years experienced 260% net growth. In this article, we use Federal Bureau of Investigation (FBI) source data to chart yearly growth using the Average Annual Growth Rate method.
Active Shooter
An “active shooter” is defined by the US government as “an individual actively engaged in killing or attempting to kill people in a confined and populated area” with the exclusion of events such as drug and gang related violence. For a more detailed explanation of "active shooter", and the full list of exclusions, please see, "What is an Active Shooter?".
Mass Shooting vs. Active Shooter Mass Killing
The term "mass shooting" has many different interpretations, but no commonly agreed upon definition. However, in 2013, the FBI began tracking "mass killings", defined by the Investigative Assistance for Violent Crimes Act of 2012 as the killing of three or more people in public spaces. While the Act does not specify, the FBI interprets mass killings as excluding the perpetrator from the three persons killed. The FBI has since published numbers for active shooter events meeting the federal "mass killings" definition for the years 2000 - 2020. It is important to note that these events comprise a minimum of one less killing than the 2005 FBI definition of "mass murder" and also exclude the same special cases excluded by the "active shooter" definition. The events, termed here "active shooter mass killings", are put forward as a useful, if imperfect, proxy for the hotly debated term of mass shootings. For a more detailed explanation of "mass shooting" and "active shooter mass killing", please see "What is a Mass Shooting?"
How the data was analyzed
Change From Prior Year Formula: (Year2 Events / Year1 Events) - 1 = % Change.
Expanded: ( 5 [Year 2001 Events] / 3 [Year 2000 Events] ) -1 = 67%.
Average Annual Growth Rate (AAGR) Formula: ( % Change1 + % Change2 + ... ) / Years = AAGR
Expanded: ( 0% + 67% + ( - 40% ) + 100% + ( - 50% ) + 33% + 0% + 75% + ( - 29% ) + 20% + 0% + 17% + 71% + ( - 33% ) + ( - 13%) + 14% + ( - 13%) + 100% + ( - 29% ) + 30% + ( - 62% ) ) / 21 Years = 260% / 21 Years = 12% AAGR.
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Endnotes:
[i] Comment: The author is indebted to the work of Rosanna Smart, Terry L. Schell, and RAND in their highly valuable Mass Shootings in the United States, a key source for this article. Citation: Rosanna Smart and Terry L. Schell, "Mass Shootings in the United States," RAND Corporation, April 15, 2021. https://www.rand.org/research/gun-policy/analysis/essays/mass-shootings.html
[ii] Federal Bureau of Investigation (FBI): Active Shooter Incidents in the United States in 2020.
[iii] Federal Bureau of Investigation (FBI): Active Shooter Incidents 20-Year Review, 2000-2019.
[iv] Federal Bureau of Investigation (FBI): Active Shooter Incidents in the United States in 2019.
[v] Federal Bureau of Investigation (FBI): Active Shooter Incidents in the United States from 2000-2018.