The fear of gun control in the United States might be one of the leading drivers behind people’s tendency to purchase firearms after a mass shooting, according to a new study based on the information-theoretic concept of transfer entropy.

The research, which appears in Nature Human Behaviour, is the first to demonstrate a causal link between media coverage of gun control policy and increases in firearm acquisition in the wake of mass shootings.

“In 2006, I left the Engineering Science and Mechanics Department at Virginia Tech, just a few months before we mourned one of the most gruesome mass shootings in history. During the Virginia Tech mass shooting, I lost one of my role models, Prof. Liviu Librescu, and I saw the lives of many friends and colleagues who were there changed forever,” said study author Maurizio Porfiri, a professor at New York University’s Tandon School of Engineering.

“As I went through the steps of my academic career at NYU, I always had in the back of my mind to find some way to contribute to research on gun violence, but only last year this desire materialized into a concrete effort that brought to this field of investigation through my experience in dynamical systems theory.”

To analyze 69 mass shootings in the United States between January 1999 and December 2017, the researchers created a database of thousands of newspaper articles on shootings and firearm regulations from The New York Times and The Washington Post. They also gathered data from the National Instant Criminal Background Check System.

Porfiri and his colleagues employed a mathematical construct known as entropy transfer, which can establish causal links between multiple variables by examining the degree to which one variable influences another.

In these analyses, influence is defined as an improved ability to make predictions about the future status of a variable (in this case, background checks) based on present knowledge of another variable (media stories about gun control policy).

Previous research has suggested that there is usually a spike in gun purchases after mass shootings. However, the new study indicates that this spike is caused by media coverage related to gun control rather than the shootings themselves.

“Through a statistically-principled analysis that looks at almost 20 years of data, this study suggests that gun acquisition is influenced by media coverage of gun control regulations, more than it is influenced by the occurrence of mass shootings,” Porfiri told PsyPost.

“The influence of media coverage is stronger in states with a less restrictive legal environment, that is, where there are less laws on guns. In this vein, people might seek to buy guns in the aftermath of a mass shooting because they fear that regulations might become stricter, thereby preventing new purchases in the future.”

The study — like all research — includes some limitations. Monthly firearm background checks were used as a proxy measure for gun purchases, but some gun sales do not result in a background check and a background check may be used to issue a concealed carry permit rather than to authorize the purchase of a new weapon.

“The study is far from being perfect, but I believe it makes an important step toward bringing quantitative methods from applied mathematics, statistics, and engineering to the field of gun violence,” Porfiri explained.

“The main limitation of the study is certainly due to the available data, which has only a resolution of one month and amounts to a couple of hundreds of samples per time series. Also, we only focused on mass shootings, which account for a small fraction of gun-related deaths, thereby calling for more research to understand the complex underpinnings of all gun violence.”

“Considering the complexity that surrounds gun acquisition and violence in the United States, it is important to extend our analysis to identify potential factors that may influence the causal relationship between gun violence and acquisition, such as socioeconomic status and political climate. We need more data to address these questions,” Porfiri said.

“I hope that this study will inspire more interdisciplinary research at the interface of criminology and applied mathematics, statistics, and engineering toward a better understanding of gun violence.”

“I strongly believe that a coordinated effort across disciplinary boundaries is needed to surpass anecdotal evidence and offer robust models that can inform policy makers. Ultimately, we hope that our study will invigorate the field of gun violence research, which is extremely behind compared to other domains related to public health,” Porfiri added.

The study, “Media Coverage and Firearm Acquisition in the Aftermath of a Mass Shooting“, was authored by Maurizio Porfiri, Raghu Ram Sattanapalle, Shinnosuke Nakayama, James Macinko, and Rifat Sipahi.