This past Friday's horrific shooting at University of California - Santa Barbara has, understandably, renewed calls for federal action on gun control. But in that specific case, one struggles to see how additional regulations could have helped. "Elliot Rodger, the self-pitying Santa Barbara killer, passed background checks—three times—as he bought his Glock and Sig Sauer pistols," Businessweek's Paul Barrett notes. "He didn’t need an 'assault weapon,' or military-style semiautomatic rifle. Ordinary handguns did just fine. He didn’t need large-capacity ammunition magazines; those are already illegal in California."

The lazy thing to conclude from that is that gun control is futile. But what it really tells us is that the biggest benefits of tougher background checks and other barriers to purchase aren't in preventing highly visible shootings like Friday's. Indeed, barely anyone talks about one of the biggest potential benefits of gun control: preventing suicides.

Why means matter

The idea that limiting access to guns could reduce suicides gets a lot of resistance from folks who question whether the method of suicide actually matters. Won't people who really want to kill themselves do it anyway, after all?

In most cases, no, they won't. Most suicides aren't committed by determined people who can't be talked out of it. They're impulsive actions which usually can be prevented by small barriers. Many survivors say they deliberated less than a day, and sometimes for only a matter of minutes, before making an attempt. Ken Baldwin, who survived a jump off the Golden Gate Bridge, once told the New Yorker's Tad Friend that as he was falling, he "instantly realized that everything in my life that I’d thought was unfixable was totally fixable — except for having just jumped."

Baldwin's change of heart isn't too unusual. 90 percent or so of people who've survived suicide attempts do not end up dying by suicide. If access to guns were more limited and the people making those attempts used less lethal means, then, if that number holds, most of the people saved won't kill themselves later on. Their lives really would have been saved.

Comparing the problems

You wouldn't know it from media coverage of guns, but gun suicides outnumber gun homicides by a considerable margin. In 2010, the last year for which the CDC provides final numbers, 19,392 people committed suicide by firearm, while 11,078 people died in gun homicides; preliminary 2011 data shows similar numbers, and historical data shows it's been this way for a while:

Because suicide in general is so much more common than homicide (in 2010 there were 38,364 total suicides and 16,259 total homicides), a lower share of suicides are committed by firearm than homicides. In 2010, about 50.5 percent of suicides were committed using a gun compared to 68 percent of homicides.

But gun suicide attempts are particularly lethal. The CDC found that in 2001, 85 percent of suicide attempts involving guns resulted in death, significantly above other methods. A study looking at hospital admissions for suicides and suicide attempts in Illinois found that 96 percent of firearm cases resulted in death, while only 6.7 percent of cases involving cuts and 6.5 percent of cases involving poisoning did.

How gun control can prevent suicide

The Harvard School of Public Health's "Means Matter" project — in general a great resource on this topic — maintains a list of studies showing just how significant a risk factor gun ownership is for suicide.

People who die from suicide are likelier to live in homes with guns than people who merely attempted suicide. States with higher rates of gun ownership have higher rates of gun suicide. It's possible to think of reasons why this may not mean that gun ownership contributes to higher suicide rates but many of the most plausible ones — say, the possibility that people in rural areas are both likelier to own guns and likelier to be depressed — don't check out; depression actually isn't higher in rural areas, for one.

So how would we go about reducing gun ownership rates? Australia's gun laws might provide a roadmap. In the aftermath of a 1996 massacre that killed 35 people, the country banned semi-automatic and automatic rifles and shotguns and instituted a mandatory buy-back program that wound up reducing gun ownership in Australia by a fifth. An equivalent program in the US would destroy about 40 million guns.

A study by Andrew Leigh of Australian National University and Christine Neill of Wilfrid Laurier University looking at subsequent trends in homicides and suicides found that a buyback of that size reduces the firearm suicide rate by 74 percent. There wasn't a significant effect on non-firearm suicides. They also found an effect on firearm homicides (a 35 to 50 percent reduction), but it wasn't statistically significant because the homicide rate in Australia normally is so low. The homicide finding has been fiercely debated, but even some critics of Leigh and Neill's study conceded the effect on suicides was real. One important caveat is that handguns were already tightly controlled in Australia in 1996, which meant that long guns were being used more frequently for suicides than they are in the US. Consequently, limiting access to long guns here might have a milder effect.

A similar thing happened when the Israeli Defense Forces stopped letting troops bring their guns home over the weekend in 2006. A study by researchers with the IDF's Division of Mental Health and Sheba Medical Center found that policy change reduced suicidesamong IDF soldiers by 40 percent, mostly due to a drop in suicides using firearms committed over weekends, with no noticeable change in weekday suicides.

Of course, the odds of an Australian-scale buyback making it past a Congress that failed to pass a weak background checks bill and even loather to spend money on, well, anything are slim. But there's some reason to think that milder efforts that limit access to guns could do some good. A study from the University of Alabama - Birmingham's Bisakha Sen and the Advisory Board's Anantachai Panjamapirom found that firearm suicide deaths are lower in states checking for mental illness and fugitive status, and in states which had background checks before the Brady law required them nationally in 1993. Of course, Congress hasn't been been keen on passing more rigorous background checks either, but it suggests that expanding background checks at the state level — as New York did after the Newtown massacre, including adding ammunition background checks — could do some good.

Further reading