Methodology

To find the number of school shootings each year since 1982, 24/7 Wall St. reviewed the Center for Homeland Defense and Security’s school shooting database. School shooting incidents include any incident where a firearm is brandished or fired at a K-12 school property for any reason at any time of day, regardless of whether there were any shooting victims. 

Supplemental data on all mass shootings came from Mother Jones’ Mass Shooting study, which categorizes mass shootings as events where three or more people are killed other than the perpetrator (or where four or more victims are killed prior to 2013). Gun ownership estimates came from historical Gallup polls, representing the percentages of respondents who said yes to the question: “Do you have a gun in your home?” Prior to the year 2000, were not conducted every year. In the cases where Gallup gun ownership data was not available for a particular year, the most recent poll results were used. Some years have multiple gallup polls, and in those cases the latest poll for that year was used.