State laws that require gun purchasers to obtain a license contingent on passing a background check performed by state or local law enforcement are associated with a 14 percent reduction in firearm homicides in large, urban counties, a new study from the Johns Hopkins Bloomberg School of Public Health found.

Studies have shown that these laws, which are sometimes called permit-to-purchase licensing laws, are associated with fewer firearm homicides at the state level. This is the first study to measure the impact of licensing laws on firearm homicides in large, urban counties, where close to two-thirds of all gun deaths in the U.S. occur.

The study was published online May 22 in the Journal of Urban Health and was written by researchers at the Johns Hopkins Center for Gun Policy and Research, based at the Johns Hopkins Bloomberg School of Public Health, and the Violence Prevention Research Program at the University of California, Davis.

Handgun licensing laws typically require prospective gun purchasers to apply directly to a state or local law enforcement agency to obtain a purchase permit, which is dependent on passing a background check, prior to approaching a seller. Many state licensing laws also require applicants to submit fingerprints.

The study also found that states that only required so-called comprehensive background checks (CBCs) - that is, did not include other licensing requirements-- were associated with a 16 percent increase in firearm homicides in the large, urban counties. In states that only require a CBC the gun seller or dealer, not law enforcement, typically carries out the background check.

"Background checks are intended to screen out prohibited individuals, and serve as the foundation upon which other gun laws are built, but they may not be sufficient on their own to decrease gun homicides," said Cassandra Crifasi, PhD, MPH, assistant professor with the Johns Hopkins Center for Gun Policy and Research and the paper's lead author. "This study extends what we know about the beneficial effects of a licensing system on gun homicides to large, urban counties across the United States."

In addition to sending potential purchasers to law enforcement and requiring fingerprints, state licensing laws provide a longer period for law enforcement to conduct background checks. These checks may have access to more records, increasing the likelihood that law enforcement can identify and screen out those with a prohibiting condition. Surveys from the Johns Hopkins Center for Gun Policy and Research find that the majority of both gun owners and non-gun owners support this policy.

CBC laws generally depend upon the use of the National Instant Criminal Background Check System (NICS), but problems with the NICS include incomplete records and the quality and timeliness of reported records. Permit-to-purchase laws provide a longer period for law enforcement to conduct background checks at the local level, and these checks may have access to additional records.

Previous research examining the impact of CBC-only laws has documented the importance of enforcement and compliance. Licensing laws, however, have consistently been associated with reductions in gun homicide.

For the study, a sample of 136 of the largest, urban counties in the U.S. was created for 1984-2015 and analyses were conducted to assess the effects of changes to the policies over time.

The study also examined the impact of right-to-carry (RTC) and stand- your-ground (SYG) laws. SYG laws give individuals expanded protections for use of lethal force in response to a perceived threat, and RTC laws make it easier for people to carry loaded, concealed firearms in public spaces.

The researchers found that counties in states that adopted SYG laws experienced a seven percent increase in firearm homicide, and counties in states with RTC laws experienced a four percent increase firearm homicide after the state's adoption of the RTC law.

"Our research finds that state laws that encourage more public gun carrying with fewer restrictions on who can carry experience more gun homicides in the state's large, urban counties than would have been expected had the law not been implemented," said Crifasi. "Similarly, stand-your-ground laws appear to make otherwise non-lethal encounters deadly if people who are carrying loaded weapons feel emboldened to use their weapons versus de-escalating a volatile situation."

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"Association between Firearm Laws and Homicide in Urban Counties" was written by Cassandra K. Crifasi, Molly Merrill-Francis, Alex McCourt, Jon S. Vernick, Garen J. Wintemute and Daniel W. Webster. All researchers are with the Johns Hopkins Center for Gun Policy and Research, with the exception of Wintemute, who is with the Violence Prevention Research Program, Department of Emergency Medicine, University of California, Davis.

Funding for the research came from the Joyce Foundation.