Mass Shootings and Civilian Armament provides the first comprehensive multi-methodological analysis of the relationship between mass shootings and firearm purchases (as proxied by background checks) in the US on national level data from 1999-2020. Since 1994, the number of civilian-owned firearms in the US has doubled to around 398 million while the population only grew by 70 million. On average, mass shootings have occurred once every two...