If he wins the presidency, Democratic Sen. Cory Booker says he will fight to deliver tougher gun control laws.

In an interview on ABC This Week, the senator from New Jersey pointed to what he said was the success of a gun licensing law in Connecticut.

"When Connecticut did licensing, their shootings dropped, their murders dropped 40%. Suicides dropped 15%," he said. "These are things that have been tried and done and that work."

We found that he correctly cited two studies, but experts said more research is needed to draw definitive conclusions.

Connecticut’s 1995 gun licensing law

Booker was referring to two different studies about the effects of a 1995 Connecticut law requiring handgun purchasers to get a license. The law was passed after a series of gang shootings in 1993 and 1994 claimed dozens of lives.

One study published in the American Journal of Public Health in 2015 examined the impact of the Connecticut law on subsequent homicides. (Researchers were from Johns Hopkins as well as University of California at Berkeley and San Francisco.)

Under the law, a prospective handgun buyer had to clear an application process that included a background check to obtain a license. The buyer also had to apply for a permit with local police.

The law also raised the legal age to buy a handgun from age 18 to 21, and it required applicants to undergo at least eight hours of gun safety training.

Researchers found the "permit to purchase" law was associated with a 40% reduction in gun homicides between 1996 and 2005. The reduction amounted to 296 lives.

They determined this by comparing Connecticut’s homicide rates after the law went into effect to rates that would have been expected if the law had never passed. Researchers used comparison data from other 39 states that did not have a similar law.

Researchers also discovered the large drop in homicides was found only in gun-related killings, not homicides caused by other means, which suggests the law was the driving force behind the reduction.

The other paper, which appeared in Preventative Medicine, examined the effects of two opposing state measures on suicide rates. In addition to the Connecticut law, Johns Hopkins researchers looked at a 2007 repeal of a 1921 Missouri law that had required anyone who wanted to buy a handgun to obtain a permit from the sheriff’s office.

Using similar methods as the homicide study, the researchers calculated the cumulative percent change in firearm suicides during the post-law change periods for Connecticut (1996–2005) and Missouri (2008–2012).

They found a 15.4% reduction in firearm suicide rates associated with Connecticut's law. Missouri's repeal of its law was associated with a 16.1% increase in firearm suicide rates.

Daniel Webster, an author of both studies and gun researcher at Johns Hopkins, said it is impossible to determine with certainty causal connections of the effects of the law.

However, researchers used the best available data and forecasted what would have happened to Connecticut’s homicide and suicide rates had the state never implemented such a law, he said.

Webster said there is debate among researchers whether one should forecast counterfactuals — what would have happened without the law, in this case — for a longer period than 10 years. While generally more data are better in research studies, too many years of data can make it harder to determine the impact of a law in some cases.

However, Webster said that he has extended his research to look at the impact of Connecticut’s gun law through 2017 and found that the trend of the impact of the law continued. Researchers plan to submit their findings to a journal.

While other experts have cited the Johns Hopkins studies, the RAND Corporation in a 2018 review of studies found the effects of licensing and permitting on homicides and suicides inconclusive. (RAND examined thousands of studies about the effects of various types of firearm laws in various places.)

RAND doesn’t consider studies about a single state to show a causal effect that can be generalized to the United States population.

"These particular studies are well-conducted and useful, but are not scientifically definitive," Terry Schell, senior behavioral scientist at RAND, told PolitiFact.

However, RAND’s "inconclusive" finding should not be treated as evidence that there is no true effect of the Connecticut policy or that Johns Hopkins findings were wrong, Schell said. RAND’s finding only concludes that more research — for example, in different states or using different methods — is needed.

David Hemenway, director of the Harvard Injury Control Research Center, explained it to us this way: the Johns Hopkins studies are strong but they are not definitive proof of the impact of these laws.

"There is a strong belief that licensing is one of those crucial things if you want to get a handle on trying to reduce gun violence," he said.

That’s different from other types of research that have been replicated multiple times, such as showing that seat belts help keep passengers safe.

Our ruling

Booker said, "When Connecticut did licensing, their shootings dropped, their murders dropped 40%. Suicides dropped 15%."

Booker is correctly citing research by Johns Hopkins University. Researchers found that Connecticut’s 1995 law was associated with a 40% reduction in gun homicides between 1996 and 2005. In a separate paper, researchers found a 15.4% reduction in firearm suicide rates associated with the law.

However, more research is needed on the topic to draw further conclusions.

We rate this statement Mostly True.