People handle guns on display at a show in Las Vegas.
People inspect guns displayed at the SHOT (Shooting, Hunting, Outdoor Trade) Show in Las Vegas in January. Steve Marcus/Reuters

States with stricter gun-control laws have fewer homicides, especially when they’re used in combination, according to a new study.

The United States remains an outlier when it comes to gun control. When Australia witnessed a mass shooting in 1996, it almost immediately enacted stricter gun-control measures, and saw faster falls in firearm deaths and suicides. After 50 people were killed in attacks on two mosques in New Zealand last month, that country’s prime minister quickly called for bans on semiautomatic guns, assault rifles, and high-capacity magazines, leading many (including Scientific American) to ask, “Why Not U.S.?” But in America, gun control remains largely the province of individual states, where policies vary widely.

A new study by researchers Michael Siegel, Molly Pahn, Ziming Xuan, Eric Fleegler, and David Hemenway finds conclusive evidence that states with stricter gun-control laws have lower rates of both murders and suicides. (Nearly two-thirds of U.S. gun deaths are suicides.) We covered an earlier study that found that states with higher rates of gun ownership had higher rates of teen suicide. Research by one of us (Richard) has found that states with stricter gun-control laws have fewer gun deaths. And a meta-analysis of more than 130 studies across 10 nations found strong evidence of the same.

But this new study scrutinizes how different types of gun laws—alone and in combination—affect homicides and suicides. The study examines 10 different types of measures, including universal background checks, age limits for handgun purchases, concealed-carry laws, assault-weapon bans, prohibiting purchases for those who have committed violent crimes, stand-your-ground laws, and bans on large-capacity ammunition magazines.

The study tracks the effects of the 10 gun laws below on gun deaths between 1991 and 2016, while controlling for factors like gun ownership, the overall violent-crime rate (excluding homicide), alcohol use, unemployment, poverty rate, and density (at the state level), all of which affect the rate of gun deaths.

State firearm laws (based on Siegel et al.)

Law Description
Universal background checks

Background checks conducted through permit requirement for all firearm sales or through required background checks for all sales.

Violent misdemeanor prohibiting for handgun possession

Handgun possession is not allowed for people who have committed a violent misdemeanor.

Age 21 limit for handgun possession

No possession of handguns allowed until age 21.

Shall-issue law Law provides no discretion to law enforcement in deciding whether to grant a concealed-carry permit. In other words, a permit must be issued unless the applicant meets pre-established disqualifying criteria.
Permitless carry No permit is required to carry a concealed handgun.
Trafficking prohibited

No one is allowed to purchase a firearm with the intent of reselling to another person who is prohibited from buying or possessing one.

Junk-gun ban

Law prohibits the sale of handguns that fail to meet certain safety requirements. In other words, a ban on guns sometimes called “Saturday night specials.”

Stand-your-ground law

Use of deadly force is allowed to be a first resort if you’re threatened in a public space in which you have the right to be present.

Assault-weapons ban Ban on sale of assault weapons beyond just assault pistols.
Large-capacity ammunition magazine ban Ban on sale of large-capacity magazines beyond just ammunition for pistols.
*May-issue law (included in study’s supplemental policy brief) Police have discretion in issuing concealed-carry permits (as opposed to “shall-issue” laws)

It’s not just that gun control works—and it does, according to the study—it’s that particular kinds of gun-control measures are significantly more effective than others. In fact, three types of restrictions are most effective, individually and in combination, in reducing the overall homicide rate. They are: universal background checks, bans on violent offenders purchasing guns, and “may-issue” laws (which give police discretion in issuing concealed-carry permits).

Universal background checks are associated with a nearly 15 percent drop in the homicide rate. Measures that prohibit people who committed a violent crime from owning a handgun are associated with an even larger reduction in homicide, 18 percent. Conversely, requiring police to approve concealed-carry permits unless the applicant meets explicitly stated exclusion criteria—so-called “shall-issue” laws—are associated with a nearly 10 percent higher homicide rate. None of the other seven firearm laws had a statistically significant association with the homicide rate when controlling for other factors.

Four types of laws were associated with the suicide rate, but only two had statistically significant relationships with it after controlling for all 10: permitless carry laws and bans on junk guns (these laws prohibit the sale of handguns that fail to meet certain safety requirements). Junk-gun bans are associated with a 6.4 percent reduction in overall suicide rates, whereas not requiring a permit for concealed carry was associated with a 5.1 percent increase in suicide rates. None of the other laws had statistically significant relationships with overall suicide rates.

An analysis the researchers did in a related policy brief shows that gun-control restrictions work even better when they are enacted in combination. States with all three of the most effective measures—universal background checks, bans on violent offenders, and “may-issue” laws (which give police discretion in issuing concealed-carry permits)—had homicide rates that were 36 percent lower. States with two of these measures had 13-percent lower rates, and those with just one had 6-percent lower rates.

Those are big differences. Over the study period, more than 350,000 homicides were committed in America. But the homicide rate varies widely across U.S. states, as the study points out. Over the study period, it ranged from a low of 1.4 per 100,000 in New Hampshire to 12.7 per 100,000 in Louisiana; the age-adjusted firearm homicide rate ranged from 0.7 per 100,000 in New Hampshire to 9.8 per 100,000 in Louisiana.

The most effective gun-control measures are those that regulate who has legal access to guns as opposed to what kinds of guns they have access to, the study concludes. Especially effective are measures that restrict the access of people with a history of violence.

Certain kinds of gun-control measures have more public support than others. For example, a large majority of Americans support universal background checks, including a whopping 97 percent of people in gun-owning households. Meanwhile, just two-thirds of Americans and roughly half of people in gun-owning households support assault-weapons bans.

The researchers note in their policy brief:

The underlying goal of firearm policy should be to find the most effective ways of limiting access to firearms among individuals who are shown to be potentially dangerous based on their criminal history without casting the net so wide as to prevent law-abiding citizens from purchasing or possessing guns. This is precisely what our research suggests would be most effective: identifying people who are at the highest risk for violence based on a past history of violence or the presence of a restraining order and stringently enforcing that gun possession prohibition.

Ultimately, this is strategic and useful advice for policymakers, gun-control advocates, and all Americans who would like to see the nation finally make progress in restricting guns and bringing down high homicide rates. Focusing on who does and doesn’t have access to guns—especially violent offenders—appears more effective, and more politically feasible, than trying to limit access to this or that kind of firearm.

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