States that require background checks for all handgun sales have significantly fewer mass shootings than states without them, according to a new analysis by Everytown for Gun Safety,a gun violence prevention organization backed by former New York City Mayor Michael Bloomberg.
Under federal law, licensed gun dealers are mandated to conduct criminal background checks to identify those who are prohibited from owning guns. But in many states, individuals can skirt background checks by purchasing a gun online or through private sellers. Eighteen states and the District of Columbia have closed that loophole by requiring background checks for all handgun sales, including online and at gun shows.
Between January 2009 and July 2015, Everytown identified 133 mass shootings in the U.S. -- defined as as incidents in which at least four people were killed with a gun. Controlling for population, states that required background checks saw 52 percent fewer mass shootings than those without them.
Not that surprisingly, states with mandated background checks also saw 63 percent fewer mass shootings committed by individuals barred from gun ownership. Nationally during that period, nearly 40 percent of mass shootings were perpetrated by people prohibited by federal law from possessing guns.