There are so many different numbers because there’s no single agreed-upon meaning of “mass shooting.” Researchers, nonprofit trackers, and the media use different definitions.
The government, for its part, has no official definition. In 2012, Congress defined “mass killings,” but in a limited context. The next year, the Congressional Research Service adopted a different definition for “public mass shooting.” The FBI doesn’t define “mass shooting” — except it has defined “mass murder” and “active shooter,” different concepts entirely.
The debate over which definition is best is tricky. But this isn’t just a matter of semantics — nor is it just a debate researchers and academics should care about. How we think about what is and isn’t a “mass shooting” influences how we and our lawmakers respond to these events. Prevention programs, new legislation, and policy may not be effective if the problem they’re trying to address isn’t clearly defined.
Different uses of the term affect public perception of the severity of the problem, too. Narrower definitions can ignore victims who have historically been harmed by mass-casualty violence — just not the kind that makes national news. At The Trace, we often use the nonprofit Gun Violence Archive’s definition, a broad one that includes shootings in which four or more people are shot, not necessarily killed, and not including the shooter. But at other times, we have explored more stringent definitions or subset the Gun Violence Archive data.
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Much of the debate over how to define a mass shooting has come down to casualty or fatality counts. From the 1980s through the early 2010s, researchers generally agreed on a threshold of four victims killed in a premeditated attack, with some additional requirements.
But it’s not hard to show the cracks in that definition. Take the 1998 shooting at Thurston High School in Oregon: Two people were murdered at school, and 25 others were shot.
“How do you tell a school with 27 people being struck by gunfire that it is not a mass shooting?” researcher Jaclyn Schildkraut, the executive director of the Regional Gun Violence Research Consortium at the Rockefeller Institute of Government, told me. It highlights the problems with a definition that centers on a victim count. No matter what number you pick, it’s going to be arbitrary.
Another example is the 2022 New York Subway shooting, in which 10 people were wounded by a shooter who fired more than 30 rounds on a crowded train. No one died, but most people still refer to that as a mass shooting, even though it wouldn’t qualify under most definitions.
“There’s a million reasons why people will get shot and don’t die, right,” said Schildkruat, who recently co-authored a textbook chapter exploring mass shooting definitions. “How fast is medical assistance rendered? What type of bullet? What type of gun are you shot with? Where on your person are you shot? Distance to a trauma center? All of these other things play into it. It doesn’t mean that the individual intended for you not to die.”
A premeditated attack targeting six victims indiscriminately at a mall is very different from a father shooting and killing five members of his family. Even though these shootings may or may not qualify as “mass shootings,” each deserves the attention and support needed to prevent future similar tragedies. But a single policy prescription isn’t going to prevent both types of shootings. And on the other hand, even when shootings and shooters are similar in motivation, circumstance, and context, they can have vastly different death or injury tolls, but still respond similarly to different prevention strategies.
Take Emergency Risk Protection Orders. These laws, often referred to as “red flag” laws, allow authorities to seize guns from people who have been deemed dangerous by a court.
“ERPOs are going to be highly, highly effective in a premeditated mass shooting if the warning signs are put together,” Schildkraut told me. But “you don’t have the window of opportunity if it’s a firefight that escalates to a shooting with multiple people. You can’t go get an ERPO, come back, and stop what’s going to happen five seconds later.”
Another proposed solution is a ban on assault weapons. Most mass shootings, regardless of the definition used, involve handguns, not semiautomatic rifles. But the most deadly mass shootings have involved assault weapons, and the number appears to be increasing. In that case, to evaluate an assault weapons ban’s effectiveness, looking specifically at shootings with higher fatalities could prove valuable.
Many “mass shooting” definitions exclude shootings that result from the commission of another crime, like robbery or burglary, and those that are precipitated by alleged street gang conflict (setting aside the issues with the way we view gang conflict). These types of shootings may call for increased investments in gang interdiction or community-based violence prevention programs, and may not be prevented by ERPOs or an assault weapons ban. The same could apply to other crisis interventions, domestic violence prevention programs, and mental health supports. They may work on one mass shooting, but not another, and an understanding devoid of the nuances can obscure that reality.
With that in mind, maybe it’s best not to have a single definition of “mass shooting,” and instead create space to explore the motivations and precipitating factors, recognizing that there are different types of mass shootings and no one-size-fits-all solution.
Researchers and some trackers are already doing a version of this. Take USA TODAY, the Associated Press, and Northeastern University’s Mass Killing Database as an example. In addition to other mass fatality attacks, it tracks mass shootings and divides them into public and nonpublic, and subdivides nonpublic further into family-related and felony-related. (It does maintain a fatality requirement.)
“How we deal with one versus the other is very different,” James Alan Fox, the Northeastern University criminology professor who oversees the USA TODAY/AP tracker, told me. “The family ones are very different. They say a lot about how we deal with domestic violence, how we deal with people who lost their job, and are struggling to feed their family.”
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We know from years of research that other types of violence have similar stratifications. There are murders committed during a robbery, people who kill their romantic partners, people who shoot a person they don’t like or out of retaliation. And we recognize the diverse causes, circumstances, and precipitating factors, and how different strategies may be better able to prevent them in the future.
“All of those are different, and we don’t seem to argue that … they require us to look at and address them through different lenses,” Schildkraut told me. “But for some reason, we can’t seem to wrap our minds around mass shootings also having those same contextual differences.”
The definitions matter for prevention, but they shouldn’t come at the expense of victims. Some attempts to define mass shootings in law have done just that: excluded victims from resources in cases where the number of victims was not “sufficiently large.”
“At the end of the day, that definition only goes so far,” Schildkraut told me. “And if we’re going to sit here and cherry-pick who we’re going to include, then a lot of people who have been impacted aren’t going to get the services and support they need.”