Gun control really works — here's the science to prove it

After last week's mass shooting at a Florida high school, many in the US are wondering what sort of gun-control measures could prevent more gun violence.
Despite some restrictions on gun research, scientists have sought to evaluate whether specific policies effectively reduce gun deaths.
Policies that seem to reduce rates of gun violence include stricter background checks, limiting access to dangerous weapons, and prohibiting domestic abusers from owning weapons.

There are close to as many guns in the US as there are people. There may be more, or there may be fewer, depending on which study you look at — there's no exact count, since there isn't a national database of gun purchases or firearm owners, and federal law does not require a prospective gun owner to get a license or permit.

That's one of the many obstacles researchers come up against when trying to evaluate why so many people die from guns in the US.

But as the country tries to figure what — if anything — can be done in the wake of yet last week's mass shooting at Marjory Stoneman Douglas High School in Florida, it's worth taking a look at the evidence we have on the effects of gun regulations.

Despite some congressional limitations on gun research, scientists have sought to evaluate the effects of gun-control legislation in the US and in other places around the world.

Here's what the data shows.

Making it easier to carry concealed guns increases the number of gun homicides.

States that have so-called right-to-carry laws require them to issue concealed-carry permits to anyone who is allowed to own guns and meets the necessary conditions.

Many people have argued that right-to-carry laws deter crime because there would be more armed people around to stop a shooter. Though that idea was supported by a controversial 1997 analysis, recent and more thorough analyses have found the opposite effect.

One recent study found that such laws increased the rate of firearm homicides by 9% when homicide rates were compared state-by-state. That could be because confrontations were more likely to escalate to a shooting, or because there were more guns around that could be stolen, or some other factor.

A spike in gun purchases after the 2012 shooting at Sandy Hook Elementary School led to an increase in accidental gun deaths, especially among kids.

Research has found that when people are around more guns, they're more likely to end up dying from accidental shootings.

After a 20-year-old man killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Connecticut, in December 2012, calls for legislation aimed at limiting access to firearms resulted in what's now become a predictable phenomenon after shootings: people bought lots of guns.

With more guns around in the following months, the rate of accidental deaths related to firearms rose sharply, especially among children, a recent study published in the journal Science found.

According to the researchers' calculations, 40 adults and 20 children died as a result of those gun purchases.

Barring people convicted of domestic abuse from owning guns has a huge effect on the number of gun deaths.

The so-called Lautenberg amendment to the 1968 Gun Control Act disqualifies people with a misdemeanor conviction for domestic violence from buying or owning weapons.

Researchers found that gun murders of female intimate partners decreased by 17% as a result of the amendment.

Laws that call for longer sentences for gun crimes also seem to help a little.

Gun-robbery rates have gone down in states that have approved longer sentences for assault or robbery with a gun.

In the 1970s and 1980s, there were 30 "add-on" sentencing laws calling for additional prison time for people convicted of robbery or assault with a gun.

A 40-year-analysis found that gun-robbery rates dropped by about 5% in the years after the sentencing laws were enacted.

States with stricter gun-control laws that spend more money on education and mental-health care have fewer school shootings.

One recent study found that a smaller number of school shootings was linked with stricter background checks for weapon and ammunition purchases as well as more money spent on education and mental-health care.

Though school shootings are not the most common form of gun violence, a recent spike in these types of events in the US has prompted concern. There was an average of one school shooting a year from 1966 to 2008, but an average of one per week from 2013 to 2015, the study found.

The researchers said that based on available data, it was difficult to say which factor was most important in reducing shootings in schools.

However, mental-health treatment is unlikely to be solely responsible, as people with mental illness are more likely to be a victim of violence than a perpetrator. Though about 20% of Americans have some form of mental illness, people with a serious mental-health problem account for only about 3% of violent crime.

After Congress let a 1994 ban on assault weapons expire in 2004, gun massacre deaths skyrocketed.

Arguments about the exact meaning of "assault weapon" obfuscate an important point: When people in the US were allowed to start buying military-style firearms with high-capacity magazines, the number of people dying in gun massacres, defined as shootings in which at least six people die, shot up.

The number of gun massacres and massacre deaths decreased by 37% and 43% after the 1994 ban on assault weapons went into effect, one researcher found. After it expired in 2004, they shot up by 183% and 239%.

There's debate over the effectiveness of this legislation in reducing overall gun crime or firearm deaths, as most gun deaths in the US are suicides and most murders involve a handgun.

But most of the deadliest mass shootings in recent US history have one big thing in common: They involved a military-style weapon with a high-capacity magazine.

Reducing access to guns could reduce the number of suicides in the US.

Some gun-rights advocates argue that if you limit access to guns, people will just find other ways to kill themselves or others.

But data indicates that this "substitution hypothesis" is not correct.

More than 60% of gun deaths in the US are suicides, and research has found that people are most likely to try to kill themselves shortly after they decide to do so. People who attempt to do that with a gun as opposed to another method are much more likely to kill themselves.

Data from other countries supports restricting gun access, too. When the Israel Defense Forces stopped letting troops bring weapons home on the weekends, suicide rates dropped by 40%, one study found.

Historically, suicides dropped after the UK switched from coal-gas ovens — which used a gas that people inhaled to kill themselves — to another fuel. The country saw an increase in the use of other methods to attempt suicide, but it did not offset the drop in suicides by coal gas.

Weapons buyback programs have been successful in reducing mass shootings.

After at 1996 mass shooting left 35 people dead in Australia, the country said "enough."

Leaders swiftly enacted gun-control legislation and set up a program for citizens to sell their weapons back to the government so they could be destroyed.

The initiative seems to have been successful; firearm suicides were found to have dropped by 65% and homicides by 59% over the next 10 years.

While Australia had seen 13 mass shootings — defined as five or more deaths — in the 18 years before the 1996 massacre, there have been none there since.

It's possible that some of those declines were part of other trends. But either way, getting many guns off the streets and out of shops has been connected to big drops in gun deaths in Australia.

The US has a higher rate of gun violence than any other similarly wealthy country. Why not try to change that?

The US has far more mass shootings than just about any country in the world. Of countries with at least 10 million people, there are more mass shootings per capita in only Yemen, which has the second-highest per-capita rate of gun ownership (the US has the highest).

Even other countries with lots of guns, like Switzerland, have far fewer firearm deaths.

In Switzerland, however, most people gain access to weapons because of military service that provides training; other prospective purchasers have to go through a multiweek background check. Authorities there also prohibit some citizens whom psychologists deem a potential risk from owning weapons.

The US is not inherently a more violent society. What sets the country apart is that it has a lot of guns that are still really easy to get. And the data that we have indicates that some gun-control measures — like banning some types of weapons, improving background checks, and putting more restrictions on weapon access — could help.

Analyzing that data and gathering more information could help leaders determine what sort of changes could help prevent another Parkland, Las Vegas, or Sandy Hook.

Or we could do nothing and wait for the same thing to happen again.