Adam Lankford (2016) claims that the United States accounted for 31 percent of the world’s public mass shooters over the 47 years from 1966 to 2012. After four years of extensive worldwide media coverage, Lankford—in response to our paper (Lott and Moody 2019)—finally made one of his datasets available. In doing so, he revealed that he used a definition of public mass shootings that is inconsistent with those of the FBI, the Department of Homeland Security, and the New York Police Department that he had claimed to be following. We find that his dataset does not even follow his own...