When it comes to gun ownership, the US blows the rest of the world out of the water. And the research on guns suggests that's probably contributing to our gun murder problem — one that the 74 school shootings that have happened since Sandy Hook demonstrate isn't yet under control.
Here's a map of firearm ownership around the world, using 2012 data compiled by The Guardian. The United States has nearly twice as many guns per 100 people as the next closest, Yemen — 88.8 guns per 100 as opposed to 54.8 in Yemen. Here's how that looks mapped:
How does this relate to homicide rates? Not simply. For instance, the United States has over 12 times as many guns per person as Honduras, but the 2012 US gun homicide rate per 100,000 people (2.97) is 1/22 of Honduras' (68.43). That's because, while guns make murder easier, wealthy industrialized countries generally have significantly lower rates of violent crime than comparatively impoverished ones.
But when you compare the United States to nations like Britain and Japan, it becomes clear that firearm ownership contributes to America's murder problem. The American firearm homicide rate is about 20 times the average among Organization for Economic Cooperation and Development countries (excluding Mexico).
Harvard researchers Daniel Hemenway and Matthew Miller examined 26 developed countries, and checked whether gun ownership correlated with murder rates. They found that "a highly significant positive correlation between total homicide rates and both proxies for gun availability." They also didn't find much evidence that a higher rate of gun murders led to lower rates of other kinds of murder (i.e., stabbings).
Interestingly, these results tended to hold true even when you exclude the United States and its super-high homicide and gun-ownership rates. "More guns are associated with more homicides across industrialized countries," Hemenway and Miller conclude.
Data from inside the United States suggests the same thing. A recent, highly sophisticated study found that, once you control for general crime rates and other confounding factors, "each 1 percentage point increase in proportion of household gun ownership" translated to a 0.9 percent increase in homicides. A meta-analysis — study of studies — found a strong consensus among researchers that access to guns correlated with higher homicide rates in the United States.
So it seems very, very likely that the US' exceptional rate of firearm ownership is contributing to its exceptionally high murder rate. But it's not all bad news: the murder rate is falling sharply, both inside the United States and around the world. There's a lot of reasons why this might be true, including smarter policing methods, a decline in the crack and heroin epidemics, and the removal of toxins like lead from the environment. Thankfully, these factors are dramatically lowering crime rates worldwide despite the massive quantity of guns in the United States and elsewhere.