There’s plenty to digest from today’s Senate Judiciary Committee hearing on guns, but it’s worth setting the record straight about a key study that “proved,” as two Republican witnesses claimed, that the 1994 Assault Weapons Ban was a failure. The study did no such thing.

The study in question was the Department of Justice’s official assessment of the ban, which was completed when it expired in 2004. Congress mandated that the executive branch conduct the study, which was carried out on behalf of the DoJ by researchers at the University of Pennsylvania, led by criminologists Christopher Koper.

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If you listened to the testimony today of Wayne LaPierre, the executive vice president of the NRA, or David Kopel, a law professor and researcher at the libertarian Cato Institute, the study’s findings were unequivocal.

“Independent studies, including a study from the Clinton Justice Department, proved that ban had no impact on lowering crime,” LaPierre said. A footnote in his prepared testimony indicated he was referring to the Koper study.

Cato’s Kopel dwelled on the study at length, spending several minutes discussing its history and findings. “We do not have to speculate about whether ‘assault weapon’ bans do any good. A Department of Justice study commissioned by the Clinton administration found that they do not,” he explained. “The study found the [Sen. Dianne] Feinstein ban to be a complete failure.”

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So is that what the study said? No, according to the author of the study himself. I emailed Koper, now at George Mason University, after the hearing to note that I had a fairly different reading of his paper from that of LaPierre and Koper, and asked if he could sort it out.

“I agree with your reading of our 2004 study,” Koper replied. You can read the full study for yourself here and see that while it was not a ringing endorsement of the assault weapons ban, as many gun control advocates had hoped, it hardly “proved” the law to be a failure, as LaPierre claims. To the contrary, it found some encouraging signs, like an average 40 percent drop in the number of assault weapons used in crimes (some cities saw a drop of over 70 percent) and some benefit from the ban on high-capacity magazines.

But mostly, the study was inconclusive. Not enough time had passed for the ban’s effect to be fully felt and there were too many loopholes to get a good read on its effect. For instance, the number of high-capacity magazines in the country actually increased during time of the ban because it was still legal to import magazines made in other countries before the law went into effect. Meanwhile, numerous other variables contributed to the drop in crime during that decade, including better policing and the end of the crack epidemic.

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In his testimony, Cato’s Kopel zeroed in on this passage from the study: “We cannot clearly credit the ban with any of the nation’s recent drop in gun violence.”

By the same token, the study didn’t rule out the ban as a contributor to the drop in crime. Just because something can’t be proven does not mean that the opposite is automatically true.

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Meanwhile, the very next sentence after Kopel’s reads: “However, the ban’s exemption of millions of pre-ban AWs and LCMs ensured that the effects of the law would occur only gradually. Those effects are still unfolding and may not be fully felt for several years into the future.”

For more, study author Koper pointed me to an Op-Ed he wrote in the Baltimore Sun in 2004. “So is the ban working?” he asked rhetorically in the essay. “It’s a work in progress,” he answered.

There’s a big difference between “a work in a progress” and a failure. And there’s a big difference between inconclusive results and proof that something was fruitless. But LaPierre and Kopel would rather pretend there is not.