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Member Research & Reports

Member Research & Reports

Johns Hopkins: Researchers Recommend Standard Definition of “Mass Shooting”

A new study led by researchers at the Johns Hopkins Bloomberg School of Public Health highlights inconsistencies in five different databases used to collect information on mass shooting events. The number of mass shootings, average number of individuals killed per mass shooting, and number of total mass shooting victims varied depending on which definition of “mass shooting” was applied and which database was used. The paper was published online December 10 in Injury Epidemiology.

Lead author Ms. Marisa Booty, a senior research data analyst at the Johns Hopkins Center for Gun Policy and Research, and coauthors recommend defining “mass shooting” as four or more casualties, not including the shooter, regardless of location. Applying this definition captures individuals who are both fatally and nonfatally injured, as well as gang- or drug-related events.

Currently, there is no federal definition of “mass shooting.” Establishing a standard mass shooting definition would improve public awareness and understanding of mass shootings as well as research credibility when presenting evidence to policymakers.

Taking 2017 data from five databases — the Gun Violence Archive, Everytown for Gun Safety, a Mother Jones Investigation, Federal Bureau of Investigation (FBI)’s record of active shooter incidents, and the FBI’s Supplementary Homicide Report — the researchers applied different definitions of “mass shooting.” They found that the number of mass shootings varied from 11 to 346 depending on the database’s definition. The total number of fatalities varied from 612 to 2,240. Only two shootings were found in all databases.

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