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Why this gun control study might be too good to be true

A customer looks at a pistol at a vendor's display at a gun show held by Florida Gun Shows in Miami in January.  (AP Photo/Lynne Sladky)

A prestigious medical journal just published a new study of gun deaths with shocking results: if just three gun control laws were adopted nationwide, the researchers found, deaths from firearms could be cut by more than 90 percent.

It's a reduction so staggering that it sounds hard to believe. And according to two outside scientists, we shouldn't.

"That’s too big -- I don’t believe that," said David Hemenway, a professor of health policy at the Harvard T.H. Chan School of Public Health. "These laws are not that strong. I would just be flabbergasted; I’d bet the house if you did [implement] these laws, if you had these three laws and enforced them really well and reduced gun deaths by 10 percent, you'd be ecstatic."

"Briefly, this is not a credible study and no cause and effect inferences should be made from it," Daniel Webster, director of the Johns Hopkins Center for Gun Policy & Research wrote in an e-mail.

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The lead author, epidemiologist Bindu Kalesan of Boston University, said that the study published in The Lancet provides policymakers the hard evidence they need to prioritize individual gun control laws that would have the biggest impact: background checks for gun and ammunition buyers and ballistic fingerprinting that allows bullets to be matched to the guns that fired them. Implementing background checks for gun buyers at the federal level, alone, would cut firearm deaths in half, the study found.

If ammunition background checks and ballistic fingerprinting were also implemented at the federal level, the study finds, the 2010 rate of death in the U.S. from firearms, 10 per 100,000, could drop to less than 1 per 100,000.

"We know that's a stretch, but we still think we can," Kalesan said.

To critics who do not believe a 90 percent decline is realistic, she points to two states: Louisiana and Massachusetts. In Louisiana, 19 of 100,000 people died of firearm deaths in 2010. In Massachusetts, which has stricter gun control laws, that rate is 4 per 100,000. She and colleagues controlled in the study for many of the factors that could influence likelihood of gun death beyond gun control policies -- including unemployment, gun ownership, gun export rates and non-firearm homicides.

"The validity has to be established with the next steps. We provide the first evidence that the three laws may reduce gun death rates. Now for the next step. Seldom is research a 1-stop process," Kalesan wrote in an e-mail.

But Webster and Hemenway -- who both say there is a growing and compelling body of evidence that gun control, and particularly background checks, do work -- cautioned against reading too much into some of its specific findings.

Why the impasse?

As anyone who has read a medical study knows, trying to parse cause and effect merely by observing the world around us is complex. Does coffee make us healthier, or is there something subtly different about coffee drinkers and those who don't partake?

Well, the same thing applies to understanding gun control laws. People may have very different inherent risks of death by firearm simply depending on whether they live in a rural or urban area. And while gun control laws may affect death from firearms, so will other factors, such as urban environments, poverty and gang violence.

Kalesan's team made an effort to account for differences that could change risk of firearm death in different states. But Webster and Hemenway said that there were many other factors that can influence a person's likelihood of dying by gunshot.

Hemenway pointed out that this isn't a flaw unique to this study -- the entire literature on gun policy comes with inherent limitations due to the nature of the data, and he suggested it is best to think of this new study as a part of the whole instead of as a policy prescription for how to do away with gun deaths. Taken together with a bunch of other research, it supports the broad idea that gun control laws work.

Some of the particulars of the study, however, are less clear. For example, the study found that ballistic fingerprint laws that require bullets to be able to be traced by guns had the third biggest effect on reducing overall firearm deaths and the strongest effect on preventing suicide death. Webster said that those fingerprinting laws aren't even currently being implemented, raising the question of how they would prevent gun deaths -- and particularly in suicides where tracing the bullet to the gun hardly seems like a deterrent. Kalesan said that that the laws would result in fewer guns, and said the study wasn't designed to distinguish how policy contributions to suicide or homicide deaths.

In an accompanying comment, Hemenway pointed out possible statistical problems and questioned its finding that nine minor laws might increase firearm fatalities, such as police inspection of firearm dealers or required theft reporting by gun dealers.

Instead of assigning too much importance to those findings, he thinks its reasonable to look at the study as yet another piece of supporting evidence for the broader idea gun control works.

But Webster took a different perspective, noting that any research on the effects of gun control policy can be politicized and that a high-profile study that is flawed but in favor of gun control laws could shake people's faith in the science and fuel critics to question the study's ultimate conclusion that gun control works. He said he frequently finds himself explaining to policy makers and the public that they should be cautious in accepting research that hasn't been peer-reviewed and published in a journal.

"What I find both puzzling and troubling is this very flawed piece of research is published in one of the most prestigious scientific journals around," Webster said in an interview."Something went awry here, and it harms public trust."

This story has been updated.

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