This blog is a part of our series, “Perspectives in Crime” where we explore leading academic studies that touch on crime data.

The prevalence of mass shootings in the United States has increased in recent years. The capacity for these attacks to happen almost anywhere and anytime have struck a particular chord of anxiety among the public, and the phenomena is of pressing concern to criminologists, policy makers, law enforcement, and security professionals.

Bar graph showing the number of mass shootings per year, 2014-2022. 2022 is greyed out to show the year is still in progress. The highest bars are 2021 and 2020, with over 600 mass shootings each. The next highest is 2022, in progress. Then 2019 at just over 400. The rest of the years are under 400.
Figure 1 shows Mass Shootings (4 or more victims shot) since 2014. Source: Gun Violence Archive.

While highly difficult to anticipate, a growing arena of scholarship have begun to utilize empirical evidence to understand why and when these events may occur.  In particular, a series of studies have traced the potential contagion nature of active shooting scenarios. Using the analytical toolkits of public health has proven a compelling lens for understanding how violent crime moves through a community. (Our recent “Epidemic of Gun Violence” blog recently summarized a study that employed network modeling, often used in context of tracing a respiratory pathogen, to model gun violence in Chicago.)

Sherry Towers, Andres Gomez-LIevano, Maryam Khan, Anuj Mubayi, Carlos Castillo-Chavez working together at Arizona State University and Northeastern Illinois University published the study “Contagion in Mass Killings and School Shootings” in 2015. They utilized mass killings data from USA Today, school shootings data from the Brady Campaign, measurements of state gun ownership rates and mental illness prevalence, and rankings from the Brady Campaign on state firearm legislation to investigate the factors that contribute to episodes of mass violence. 

Increased probability of a mass shooting event

Towers et al’s (2015) analysis found an increased probability of both mass shooting and school shooting events in the 13 days directly following a prior shooting incident. For instances of mass violence, the 13-day probabilistic increase was the magnitude of at least 0.3 new incidents. The increase for school shootings was an average of 0.22 new incidents per shooting incident. State prevalence for firearm ownership was associated with the likelihood of a mass shooting or school shooting event. Researchers found no statistically significant relationship between state prevalence of mental health or the strength of firearm legislation in the likelihood of shootings occurring. 

The relationship between mass shootings and media coverage

Michael Jetter and Jay Walker’s 2018 study “The Effect of Media Coverage on Mass Shootings” published by the Institute of Labor Economics, studied the relationship of media coverage on shootings and subsequent shootings. Jetter and Walker (2018) used the Gun Violence Archive and the Vanderbilt Television News Archive, employing data specifically for ABC World News Tonight, the 30 minute nightly national news program.  

During the study period (2013-2016), this program averaged eight million viewers daily, making it the most watched national evening news programs. Researchers tracked news segments that mentioned the term shooter or shooting as well as searches with alternative and related terms including rampage and gunman to identify coverage of mass shooting events. They summed the total time in seconds covering these stories and divided by total seconds for all news segments of that day. On average, they found an average of 3.7% of nightly news coverage during the study period was about mass shooting incidents.

Jetter and Walker (2018) found that despite shootings being more likely to happen on the weekend, news coverage focused on shootings received an average of approximately 4% of airtime every day of the week. They also analyzed which months shootings occurred and their related media coverage. They found a strong seasonality in the breakdown of mass shootings per day, with the warmer months seeing an increased number of shooting events and January typically being the annual low point for events. Despite this, media coverage of mass shootings spiked in December and had the lowest relative airtime at the beginning of the year, January through March.

Line graph showing a rise in prediction additional shootings in the days following inital media coverage. The line peaks at just above 0.8 additional shootings at about 7 days after initial coverage.
Figure 2

Violence causes violence

Both studies approaching contagion effects in relation to mass shootings found support for the hypothesis that violence begets more violent. Mass shooting and school shooting events appears to produce a short-term increase of the likelihood that comparable events will occur.

Additionally, the degree of salience and attention given to an event appears to also impact the likelihood of future events. Many media outlets have already begun to alter the way they cover incidents of mass violence, reducing coverage and images oriented around shooters, and instead placing significance on their victims. Further research and potential policy interventions will continue to provide guidance in approaching this social problem.

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Published September 30, 2022


Gun Violence Archive. Accessed 9/18/22.  

Jetter M, Walker J .(2018). The Effect of Media Coverage on Mass Shootings. IZA Institute of Labor Economics Discussion Paper Series. 

Towers S, Gomez-Lievano A, Khan M, Mubayi A, Castillo-Chavez C. (2015). Contagion in Mass Killings and School Shootings. PLoS ONE 10(7).