The share of Americans killed by guns is without parallel in the developed world. The most striking statistic: 87 percent of children killed by guns in 23 of the world's most developed, wealthiest countries were Americans.

That comes from a 2011 analysis of 2003 mortality data from members of the Organization for Economic Cooperation and Development, a group of wealthy, developed nations. It found that in general, Americans were killed by guns far more frequently than people in the other 22 countries, including Australia, Canada, the United Kingdom, France, and Hungary. They were also more likely to be killed, period: The American homicide rate was seven times the rate of the other 22 countries.

The other findings underscore, in the wake of the San Bernardino massacre, that this is a uniquely American problem:

Firearm homicide rates in the US were 20 times higher than in the other countries studied.

American teenagers and young adults, ages 15 through 24, were 43 times more likely to be killed by a gun than their counterparts in other wealthy, developed countries.

Among the 23 countries with a combined population of 854 million people, the US had roughly one-third of the people — and 80 percent of the gun deaths.

Regardless of whether mass killings like the one in San Bernardino are becoming more frequent, they happen far more in the US than anywhere else.