Mass shootings in the U.S.: Numbers can be deceiving

Estimates of the number of mass shootings in the U.S. varies from a mere handful to around 350, depending on who is doing the counting and how they define mass shooting. Part of the problem with reporting an exact number results the lack of an official source.

Definitions of mass shooting vary, leading to vastly different numbers

Law enforcement officers search for suspects after a shooting at the Inland Regional Center in San Bernardino, Calif., Dec. 2. (Eugene Garcia/EPA)

Since the Dec. 2 killing spree in San Bernardino, Calif., many media sources have said there have been hundreds of mass shootings in the U.S. this year alone.

But coming up with an exact number poses a challenge. In fact, it can range from a mere handful to around 350, depending on who is doing the counting.

Much depends on the definition of "mass shooting" and even then, there is quite a bit of latitude on what is included.

Gang-related shootings, for example, are included in some accountings, but not others. The FBI is among those that don't include gang shootings in their compilation.

As there are no official sources cited in U.S. media, a web site called Mass Shooting Tracker ( now seems to be the main authority for news outlets trying to provide a number.

After the shooting in San Bernardino, which killed 14 and wounded 21, Mass Shooting Tracker's count stood at 353. Or 354.

The web site has been frequently inaccessible lately, because it had "exceeded its resource limit," according to a message on the site.

Mass Shooting Tracker is based on crowd-sourced data from the GunsAreCool web page on That web page, or subreddit, listed 354 shootings for 2015 so far.

Given the volunteer nature of the data collection, there are bound to be inaccuracies. For example, GunsAreCool lists the Nov. 29 shooting at a banquet hall in Kankakee, Ill., which left five people injured, but the tracker does not.

And on Thursday, both sources dropped a shooting in May in Arlington, Va., which never met their criteria for a mass shooting in the first place.

The San Bernardino killing spree has been the deadliest mass shooting in the U.S. so far this year. (NBC/Reuters)

Due to their limited resources for tracking the shootings, GunsAreCool states that, "we can say unequivocally with 100% certainly [sic] that more mass shootings occurred in the United States during the calendar year than are reported here."

So it's probably advisable, when using the site's data, to add the phrase "at least" before citing their number.

Defining mass shooting

According to GunsAreCool and Mass Shooting Tracker, "a mass shooting is when four or more people are shot in an event, or related series of events, likely without a cooling off period."

This may include the shooter(s) themselves as well as victims shot by police while attempting to end the incident.

GunsAreCool started tracking mass shootings in 2013. The site counted 365 that year and 336 in 2014.

Mass Shooting Tracker cautions against using its numbers of dead and injured, because it doesn't update them after the initial reports of a mass shooting. 

A daughter of the late Rev. Clementa Pinckney reaches up to U.S. President Barack Obama after the president eulogized Rev. Pinckney during funeral services in Charleston, South Carolina June 26. Pinckney died when a gunman opened fire in the mass shooting at a Charleston Church. (Jonathan Ernst/Reuters)

However, the New York Times, National Public Radio, and the Globe and Mail did exactly that following the San Bernardino shooting to provide total numbers for killed and injured in mass shootings.

But the dates of the mass shootings shouldn't change. 

The list shows that the longest stretch this year without a mass shooting in the U.S. was eight days, from April 8 to 15 inclusive.

But on April 18, there were five separate mass shootings — setting a new high for a single day in 2015. That record would be matched four more times in 2015.

Huge range in number of mass shootings

The Gun Violence Archive, a nonprofit organization founded by Washington businessman Michael Klein, also tracks mass shootings. On the site's home page, its count for 2015 after the Dec. 2 shootings stood at 309 — yet they list only 300.

But its definition is also slightly different: "Four or more shot and/or killed in a single event at the same general time and location, not including the shooter."

The Mother Jones web site has also been tracking mass shootings since 2012, but it uses a much narrower definition.

To meet its criteria, an attack must have occurred in a public place and appear to have "indiscriminate mass murder" as the motive. That means it excludes cases of "armed robbery, gang violence and domestic violence in a home." 

Mother Jones also oddly adds this: "The killer, in accordance with the FBI criterion, had to have taken the lives of at least four people."

However, that FBI criterion is for mass murder, not mass shooting.

Since not everyone dies after someone shoots them with a firearm, Mother Jones' count depends on the victims' survival, and therefore the accuracy of the shooter and the quality of emergency response and care. 

Mother Jones lists just four mass shootings this year. By comparison, the list  at Gun Violence Archive has 26 mass shootings in 2015 in which four or more people were killed.

Umpqua Community College alumnus Donice Smith (L) is embraced after she said one of her former teachers was shot dead, near the site of a mass shooting at Umpqua Community College in Roseburg, Oregon Oct. 1. It was the deadliest shooting in the U.S. in 2015, until the San Bernardino shooting. (Steve Dipaola/Reuters)

No official source

We didn't find a definition of mass shooting on the FBI web site. It tracks what it calls active shooter events, which it defines as "one or more persons engaged in killing or attempting to kill multiple people in an area occupied by multiple unrelated individuals — at least one of the victims must be unrelated to the shooter."

The FBI excludes gang-related shootings from its active shooter data, even though the bureau concedes they meet the criteria, because for some reason, gang shootings "are not considered ASEs by law enforcement."

Comparing active shooter events and mass shootings sounds like the old cliché about apples and oranges. In any case, the FBI doesn't provide a number for 2015.

The Centers for Disease Control seems like another possible official source for the number of mass shootings in the U.S. But in 1996, a law was passed banning the CDC from conducting firearms research.

That year, Republican Jay Dickey served as the National Rifle Association's "point person" in Congress (Dickey's description of his role). He inserted a clause into an appropriations bill stipulating that "none of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control."

The bill also reduced the funds provided to the CDC's injury centre by $2.6 million, the amount it spent on firearms-related research the year before.

The same language appeared in subsequent appropriations bills, including this year.

Other congressional amendments also have roadblocks for U.S. government funding on firearms research, or even tracing a gun.

Ironically, in 2012, Dickey, no longer a congressman but still an NRA member, complained in a Washington Post editorial that since 1996, "there has been almost no publicly funded research on firearm injuries."

Dickey had reversed his view and advocated Washington fund research on how to prevent firearm deaths and injuries.