A gunman on Thursday night opened fire at a Lafayette, Louisiana, movie theater, reportedly killing three, including himself, and wounding nine others. The shooting came three days after the third anniversary of the spree shooting in an Aurora, Colorado, movie theater that killed 12 and injured 70.

It's disturbing and sickening that if someone were to ask about the movie theater shooting, the first response would be "which one?" — Nerdy Wonka (@NerdyWonka) July 24, 2015

Although these mass shootings make up a small portion of overall gun violence, they seem to be happening more often. And they point toward a larger truth: America is a huge outlier among developed countries when it comes to gun ownership and gun-related homicides.

1) Under one definition, public mass shootings appear to be more common since 2011

There's some debate about how to define mass shootings. But under one definition — shootings at a public place in which the shooter murdered four or more people, excluding domestic, gang, and drug violence — they appear to be getting more common, as the chart above from Mother Jones, based on an analysis from Harvard School of Public Health, shows.

But not everyone agrees with this definition. Northeastern University criminologist James Alan Fox, for example, defines mass shootings as any shooting in which at least four people were murdered. Under those terms, mass shootings don't appear to be increasing. Researchers from Harvard School of Public Health call that definition too broad, since it catches domestic, gang, and drug-related shootings that may not be considered mass shootings in layman's terms.

Using data from the Stanford Geospatial Center, which defines a mass shooting as an event in which someone shot three or more people, Vox's Soo Oh made this interactive map of mass shootings since the one at Sandy Hook Elementary School:

Although these mass shootings tend to draw a lot of media attention, they make up a fraction of a percent of overall gun violence in America. The problem with gun violence in the US reaches much further.

2) Gun violence is much more common in America than in its developed peers

Gun violence is much more common in the US than in its developed peers — and it's not even close. This chart, compiled using United Nations data collected by the Guardian's Simon Rogers, shows that America far and away leads other developed countries when it comes to gun-related homicides:

But why does the US have so many more gun homicides than other advanced countries? One possible explanation: Americans are much more likely to own guns than their peers around the world. And the empirical research shows places with more guns have more homicides.

Criminal justice experts widely recognize this is a result of cultural and policy decisions that have made firearms far more available in America than in most of the world.