In 1995, Connecticut established a "permit to purchase" law, which required a background check and eight hours of safety training for those seeking to buy a handgun.

Missouri used to have a law like that, too, but repealed it in 2007.

New research shows what happened afterward. Firearm suicide rates fell 15.4 percent in Connecticut — but rose 16.1 percent in Missouri. The study, published in the journal Preventive Medicine, only confirms what other papers have found: Making it harder to access guns correlates with fewer suicides.

Most gun deaths in the United States are suicides

There were 33,636 gun deaths in the United States in 2013. While homicides and mass shootings dominate the headlines, nearly two-thirds of those deaths — 21,175 — were suicides.

More than half of all suicides in the United States are carried out with a gun. The evidence is pretty compelling that reducing access to firearms could prevent at least some of those deaths. My colleague Dylan Matthews has written about it here:

There's a popular myth that suicidal people will find a way to kill themselves no matter what, and that closing off one method (like guns) will just lead to an increase in suicides through other methods (like hanging or overdoses). But most suicides aren't committed by determined people who can't be talked out of it. They're impulsive actions that can usually be prevented by small barriers. Many survivors say they deliberated less than a day, and sometimes for only a matter of minutes, before making a suicide 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. Ninety percent or so of people who've survived suicide attempts do not end up dying by suicide. So blocking off particularly lethal suicide methods — ones where attempts almost always lead to death — saves life.

We know suicides are more common in places that have more guns. Research from other countries, including Australia and Israel, has shown significant drops in suicides in the wake of tighter gun control. This new paper shows something similar happening in the United States.

Stricter gun control in Connecticut — and a drop in suicides

A team of researchers at Johns Hopkins University looked at Connecticut and Missouri to understand what happens when access to guns gets, respectively, harder or easier.

Estimating the effect of one new law is, as the researchers admit, tricky. There are dozens of things happening in each state that could affect suicide rates and no perfect experiment to isolate each one.

To make their best guess, though, the Hopkins researchers compared the change in suicide rates among some comparison states (those that didn't change their handgun permit laws) with Missouri and Connecticut (which did). Researchers have used similar methods to do things like estimate how many deaths Medicaid prevents — again, not a perfect study, but the best they've designed for these real-world scenarios.

That research showed that Missouri's handgun suicide rate was 16.1 percent higher over the five-year period after repeal than would be expected looking at the comparison states. Likewise, Connecticut's rate over a five-year period was 15.4 percent lower.

Suicide is a massive public health problem in the United States, and the 10th leading cause of death overall. This new research suggests pretty compelling evidence that we know at least one way to reduce suicides: Make it more difficult to obtain guns. As Dylan put it in a recent Vox video, "If someone told you there was a pollutant killing 21,000 people a year, you'd want to do something about it. It's worth asking ourselves if guns are that pollutant."