WASHINGTON — Speaking on gun violence in Minneapolis Monday, President Obama sounded a refrain similar to those coming from gun control proponents: Enacting a system of expanded background checks on gun purchases should be a simple step for lawmakers, despite debates over other parts of broader gun control platform.

Voters support such a plan, polls show, and it's gotten a bit of traction on Capitol Hill, especially with Democrats. But detractors, the National Rifle Association among them, say one of the biggest statistics gun control advocates use in advancing the measure is based on faulty research.

Obama has used the stat in the past, saying some 40 percent of guns are purchased without the buyer going through a federal background check, which is required only when someone purchases a gun from a federally-licensed dealer (unlike private sellers you might see at a gun show). Just last week, at a Senate Judiciary hearing on gun violence, Baltimore County Sheriff Jim Johnson used the stat in response to a question from Sen. Amy Klobuchar. It’s also a component of the Brady Campaign’s push for stricter gun laws.

The conservative National Review has questioned the number, and PolitiFact has broken down the claim a handful of times. Their conclusion: the stat is based on old research with a fairly small sample size, though gun violence researchers say it might still be true today.

From PolitiFact:

The original source of the 40 percent figure is a 1997 National Institute of Justice study [PDF] by researchers Philip Cook of Duke University and Jens Ludwig of the University of Chicago, who examined data from a 1994 telephone survey about gun ownership. The survey, which sampled 2,568 homes, asked owners an array of questions, including how many guns were in the house, what they were used for, how they were stored and how they were obtained.

But it’s important to note that of the 2,568 households surveyed, only 251 people answered the question about the origin of their gun

But in those answers, Cook and Ludwig found that 35.7 percent of respondents reported obtaining their gun from somewhere other than a licensed dealer. (That has been rounded up to 40 percent.) Some people answered "probably" and "probably not" if they weren’t entirely sure whether the seller was a licensed dealer. In some cases, where the respondent skipped the question about whether the gun came from a licensed dealer, the researchers made a judgment call. Ludwig said in an email that they mined answers to other questions (such as whether the gun was a gift) to guide them.

One of the study’s researchers said he has “no idea” if the number is still accurate. PolitiFact asked the opinions of a handful of experts on both sides of the gun debate, and they were divided on the current validity of the stat. PolitiFact gives the claim a “half true.”

Though lawmakers may very well end up considering several gun bills, they’ll defeat most of them (In Minneapolis, Obama called on the Senate to, at the very least, vote on some of his proposals). But background checks, as Obama said, might be one of the few areas where compromise is possible.

Polls show huge support for expanded background checks, even among members of the NRA. Gun control advocates say background checks should be an easy reform for Congress to pass, and Obama insinuated Monday that they should be considered light lifting, that the real fights lie in bans on assault weapons or high-capacity magazines.

Statistical validity aside, the NRA has opposed new background check measures until current federal laws are enforced more vigorously, CEO Wayne LaPierre said last week.

“If you’re talking about expanding that system to every hunter, to every family member, every relative all over the United States when the system already can’t handle what it has,” he said, “you’re creating an enormous federal bureaucracy, and it’s only going to hit the law-abiding people, not criminals. … It’s an unworkable, universal, federal nightmare bureaucracy being imposed under the federal government.”

Devin Henry can be reached at dhenry@minnpost.com. Follow him on Twitter: @dhenry