We then summarize findings from the literature regarding the characteristics of mass shootings, including offender characteristics, types of firearm(s) used, and community-level correlates. In this essay, we first describe different approaches for defining a mass shooting and discuss how using different definitions can influence estimates of mass shooting levels and trends. Mass shootings also frequently generate extensive media coverage related to guns, prompt political discussions about legislative initiatives for how better to prevent gun violence, and may lead to substantial state gun policy changes (Schildkraut, Elsass, and Meredith, 2018 Newman and Hartman, 2019 Luca, Malhotra, and Poliquin, 2020). These mass public shootings are rare events-they constitute less than 15 percent of all mass killings in the United States and are responsible for less than 0.5 percent of all homicides (Duwe, 2020)-but they have far-reaching impacts on citizens’ mental health, anxiety, and perceptions of safety (Lowe and Galea, 2017). There has been extensive media coverage of many incidents in the United States in which individuals have used firearms to kill large numbers of people. Incidents of mass firearm violence galvanize public attention. Implementing broader violence prevention strategies rather than focusing specifically on the most-extreme forms of such violence may be effective at reducing the occurrence and lethality of mass shootings. The rare nature of mass shootings creates challenges for accurately identifying salient predictors of risk and limits statistical power for detecting which policies may be effective in reducing mass shooting incidence or lethality. But several other characteristics that are statistically predictive of perpetration are still uncommon among offenders on an absolute level. These inconsistencies lead to different assessments of how frequently mass shootings occur and whether they are more common now than they were a decade or two ago.ĭata show that, regardless of how one defines mass shootings, perpetrators are likely to be men. For instance, when various organizations measure and report on mass shootings, the criteria they use in counting such events might differ by the minimum threshold for the number of victims, whether the victim count includes those who were not fatally injured, where the shooting occurred, whether the shooting occurred in connection to another crime, and the relationship between the shooter and the victims. Summary: There is no standard definition of what constitutes a mass shooting, and different data sources-such as media outlets, academic researchers, and law enforcement agencies-frequently use different definitions when discussing and analyzing mass shootings.

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