People opposed to gun control often have argued that they need firepower to protect themselves against criminals. Take this example from January 2013 when a Georgia woman shot a crowbar-wielding intruder who broke into her home and confronted her and her two young children [source: CBS News]. A number of armed American citizens have also used their firearms to stop or limit mass killings. Like Stephen Willeford, the armed citizen who stopped the massacre at First Baptist Church of Sutherland Spring, Texas in 2017 [source: CNN]. Gun control opponents say that a vast number of crimes are prevented by armed citizens, who either shoot an assailant — an event that happened 326 times in 2010, according to a 2012 Wall Street Journal state-by-state analysis of crime statistics — or more often, chase the would-be criminal away by brandishing a weapon [source: Palazzolo and Barry].
There is some social science to back up that thesis. Perhaps the most often-cited evidence is a 1995 study by Northwestern University School of Law researchers Gary Kleck and Marc Gertz. Based upon a random telephone survey of 5,000 Americans, they concluded that there were between 2.1 and 2.5 million defensive gun uses each year. This works out to about 1 percent use of a gun for defensive purposes [source: Kleck and Gertz].
But critics questioned whether Kleck's and Gertz's findings were reliable. Harvard public health researcher David Hemenway published a paper refuting this and pointing out that "since only 42 percent of U.S. households own firearms and victims in two-thirds of the occupied households were asleep, the 2.5 million figure requires us to believe burglary victims use their guns in self-defense more than 100 percent of the time" [source: Hemenway]. Another mid-1990s study, based upon a Justice Department survey of nearly 60,000 households, came up with a much smaller estimate of about 21,500 defensive gun uses annually [source: Committee on Law and Justice].
Even if the low-end estimates are closer to the truth, this still could mean that tens of thousands of crimes are prevented by gun owners annually. But a 2009 University of Pennsylvania School of Medicine study found that people with a gun were 4.5 times more likely to be shot in an assault than those who were unarmed.