There were between 11 and 346 mass shootings in 2017, depending on the database. The discrepancy has real-world impacts

Shortly after the school shooting in Parkland, Florida, in 2018, the research analyst Marisa Booty was tasked with updating data about mass shootings for the Center for Gun Policy and Research and Johns Hopkins University in Baltimore. But while sorting through publicly available data, she found all of the sources defined mass shootings slightly differently.

Now, Booty and her team of researchers are calling on the US government to establish a consistent definition of mass shootings. In a study published on 3 December, Booty and other researchers analyzed four commonly cited public databases and found that the reported number of mass shootings in 2017 ranged from 11 to 346.

This led to concerns about lobbyists and lawmakers only using the mass shooting data that best matches their individual agenda. The researchers say this inconsistency can slow legislative progress and affect the level of media attention on incidents that don’t meet certain standards.

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The four sources include the not-for-profit organizations Everytown for Gun Safety and the Gun Violence Archive, as well as Mother Jones and the FBI’s Supplementary Homicide Report (SHR). Mother Jones, a news organization that tracks mass shooting incidents, excludes shootings that result from domestic violence, drug deals and gang activity. The others recognize these instances but diverge when it comes to including nonfatal gunshot injuries.

“Since a lot of these definitions revolve around persons killed and fatalities, events with nonfatal injuries are easily overlooked in discussion and policy,” Booty says.

In January 2013, less than a month after 20 children and six adults were fatally shot at Sandy Hook elementary school in Connecticut, Barack Obama signed legislation that defines a “mass killing” as three or more people killed in a single incident.

Since then, mass shootings have been generally understood to mean four or more people shot and killed, excluding the shooter, in a public place. But Booty worries that this narrow definition can hinder researchers and policymakers from capturing the impact of shootings that happen in homes and on single neighborhood blocks.

“We hear about high-profile mass shootings that are happening at schools and in churches but a lot of violence in neighborhoods isn’t being as heavily weighted,” Booty says.

“Regardless of the circumstances of the incident, multiple people are being shot and potentially killed, and people are suffering lifelong consequences.”

Besides the number of fatalities and injuries, mass shootings are often distinguished by heavy news coverage that analyzes statistics and theories about what causes these tragedies. But instances of domestic and community violence often don’t receive this level of extensive media attention.

“The news has a big role to play in what we are and aren’t talking and thinking about,” says Pamela Mejia, the head researcher for the Berkeley Media Studies Group. “We can’t solve a problem that we don’t know is happening.”

Booty and her team recommend that the definition of mass shooting should be four or more people, excluding the shooter, who are shot in a single event regardless of the motive, setting or number of deaths. They hope that the federal government can agree on a consistent definition that researchers and officials can use as the basis of policy recommendations.

“We need to come together and come up with a definition that not necessarily everyone agrees on but will help us better determine the burden that mass shootings are having on the country,” Booty says.