Reason, April 2021
In the last month, the United States has seen four mass shootings in public places that killed at least four people aside from the perpetrator, including yesterday’s attack at a FedEx warehouse in Indianapolis. Prior to the Atlanta spa shootings on March 16, more than a year had elapsed without such a crime, which is the definition of public mass shootings used by the Congressional Research Service.
That pattern is consistent with data indicating that public mass shootings tend to happen in clusters, suggesting that one such crime makes others more likely. “One happens, and you see another few happen right after that,” Hamline University criminologist Jillian Peterson noted in a 2019 interview with NPR.
A 2015 PLOS One study seemed to confirm that impression. Statistician Sherry Towers and her collaborators looked at 232 “mass killings” (defined as “incidents with four or more people killed”) from 2006 through 2013, based on USA Today‘s database. They also considered 188 school shootings—defined as incidents on campus (including college campuses) during school hours, on school buses, or at school-related events (such as football games) in which at least one person was shot—from 1998 through 2013.