WASHINGTON — Some of the numbers being hurled around in the gun control debate passed their freshness date eons ago. Perhaps none is more prominent than the claim that 40 percent of gun sales take place without background checks.

The statistic is ubiquitous these days and cited as gospel by a variety of public figures and gun-control advocates, President Barack Obama among them, but it is 20 years old and was not much more than an educated guess at the time.

A 1996 law pushed by the gun-rights lobby closed the spigot on federal gun research, leaving scholars, private groups and states to pick up some pieces. Only now, under a recent order by Obama, can federally financed research resume.

No one questions that criminals get their hands on guns, and do so primarily from the off-the-books market. But no one knows how many guns skirt the criminal-check system by taking place at gun shows, in private transactions or otherwise outside the regulated channels. Public policy research is scarce on the subject.

Into this statistical vacuum rush voices of certitude.

OBAMA, on Jan. 16: “It’s time for Congress to require a universal background check for anyone trying to buy a gun. The law already requires licensed gun dealers to run background checks, and over the last 14 years that’s kept 1.5 million of the wrong people from getting their hands on a gun. But it’s hard to enforce that law when as many as 40 percent of all gun purchases are conducted without a background check. That’s not safe. That’s not smart. It’s not fair to responsible gun buyers or sellers.”

MAYORS AGAINST ILLEGAL GUNS, a coalition favoring tighter gun controls, on Tuesday: “Around 40 percent of U.S. gun transfers are conducted by unlicensed ‘private sellers’ who are not required to conduct a federal check, and who often do business at gun shows and on the Internet.”

VICE PRESIDENT JOE BIDEN, Jan. 17: “Because of the lack of the ability of federal agencies to be able to even keep records, we can’t say with absolute certainty what I’m about to say is correct. But the consensus is about 40 percent of the people who buy guns today do so outside the ... background check system.”

The facts

Biden stands alone here in acknowledging he may be saying something that isn’t right.

The claims that gun sales made without background checks comprise “more than,” “as many as,” “nearly” or “about” 40 percent of all gun sales are rooted in a poll looking broadly at gun ownership in America. Sponsored by the Justice Department through a grant to the Police Foundation, the poll’s principal relevance today is as a snapshot of the way things were when it was taken — 1994.

The research reported on the nature of gun acquisitions made in 1993 and 1994, asking people who had obtained guns then where the guns had come from and whether they thought the source was a federally licensed dealer. Transactions through licensed dealers were considered covered by the background check system, which was just then coming into effect.