‘Going postal’—committing mass murder in a public place—seems to have become a horrifying symptom of our times. The latest example, the massacre at Sandy Hook Elementary in Newtown, Connecticut, has left Americans divided as to how to proceed. Recent data on mass shootings compiled and released by Mother Jones shed some new light on the issues.

The data refer to gun homicides in the U.S., during the past three decades, committed at a single time, away from home, and involving four or more victims. What’s fascinating in these numbers, grim as they are, is that they are often merely the tip of the iceberg: the larger truth lies beneath the surface.

Number of mass shootings in the United States since 1982: 62.

That’s a startling number, to be sure. But what’s truly startling is that despite their dramatic nature, mass shootings together account for “only” 1,007 deaths over 30 years. To put that in perspective, more than 11,000 Americans were killed by guns in 2009. In Chicago alone in 2012, 500 people have been killed in homicides. In the week after Sandy Hook, 100 Americans were killed by guns.

U.S. mass shootings since 1982 in which the shooter, or shooters were men: 61.

Is anyone surprised that the majority of mass shooters were male? Probably not. But that only one of the killers was female must surely be cause for serious consideration. Gun ownership among women in the U.S. as of 2005 was roughly 13 per cent; for men it was 47 per cent. Perhaps more important though, is how likely women are to be victims of gun crime. Harvard Injury Control Research Centre puts it this way: more guns = more female violent deaths.

U.S. mass shootings since 1982 involving semiautomatic or assault weapons: 58.

All but four of 62 shootings included one or more semiautomatic handguns, or one or more assault weapons, or both. There’s a widespread belief that the Second Ammendment to the U.S. Constitution, commonly known as ‘the right to bear arms’, gives carte blanche to gun owners.

Perhaps not: the Supreme Court in District of Columbia v. Heller in 2008 affirmed “The Second Amendment right is not a right to keep and carry any weapon in any manner and for any purpose.” Hence, a ban on semiautomatic and assault weapons might not be in violation of the Second Ammendment.

U.S. mass shootings since 1982 in which shooters used weapons obtained legally: 49.

This figure does not include the two semi-automatics Adam Lanza used in the Sandy Hook shootings. They’re considered to have been illegally obtained because Lanza apparently stole them from his mother—who obtained them legally, and taught him to use them. (An important fact not dealt with in the popular ‘I Am Adam Lanza’s Mother’ post by Liza Long.) In five of the 11 cases of illegally obtained guns in the Mother Jones data set, the weapons were stolen from family members.

Incidentally, in 2004, the makers of a Bushmaster assault rifle similar to the one Adam Lanza stole were sued for allowing their product to fall into the wrong hands after it was used in the Washington, D.C. shooting spree. Since then, the NRA lobbied for, and got Congress to pass a law that protects gun manufacturers from lawsuits seeking to hold them liable for gun crimes.

U.S. mass shootings since 1982 that ended as murder-suicides: 36.

This number may be even higher, because in seven instances, the shooters were ultimately killed by law enforcement officers in scenarios viewable as suicide by cop. For obvious reasons, a lot of attention is being paid to firearm homicides. But did you know firearm suicides are more common?

U.S. mass shootings since 1982 in which shooters had shown signs of mental illness: 40.

This should be the place where gun advocates, and gun control advocates can find common ground. Responsible gun dealers must want to eliminate those who are mentally ill and at risk for violence from their pool of potential customers. But that’s not always possible right now. A mere 12 states account for the vast majority of queries to the FBI database set up for the purpose. Nineteen states have submitted fewer than 100 records each to the FBI database.

One challenge in focusing on mental illness will be not stigmatizing mentally ill people. It’s been duly noted that most mentally ill people don’t commit violent crimes. But it’s also true, as one pundit put it, that “anyone who goes into a school with a semiautomatic and kills 20 children and six adults is, by definition, mentally ill”.

U.S. mass shootings that have occurred since 2006: 25.

Gun ownership is up, way up, in the U.S. since 1982, having outpaced population growth during the period reported by the survey. There are now nearly as many guns in the U.S. as people, which means there’s more than one for every adult American. At least 118 million of those are handguns, according to Mother Jones. And recent mass shootings have caused spikes in gun sales. As gun sales have gone up, so have mass shootings. Coincidence?

U.S. mass shootings since 1982 prevented or ended by armed bystanders: 0.

The NRA’s notion, that schools should be armed to prevent massacres like the one at Sandy Hook, is not borne out by the record. Mother Jones found that an armed bystander played a role in only one of the 62 mass shootings examined—by shooting the perpetrator after he had already fled the scene.

Politically, the issue of mass shootings is a highly visible, volatile one, for obvious reasons. No one wants another Sandy Hook, any more than anyone wanted another Aurora, another Virginia Tech, another Columbine. People keep “going postal,” and the horrifying results are plain to see.

But “going postal,” however common it appears, however visible its impact, remains relatively rare—mass shootings account for a tiny fraction of the deaths associated with guns in the United States today.

Put bluntly, mass shootings are not the problem. They are a symptom of the problem. The problem is as simple as the numbers; the solution is as complicated as the politics that surround it.