The share of Americans who obtained a gun without first undergoing a background check is dramatically lower than previous estimates, researchers at Harvard and Northeastern universities have determined. The finding re-shapes one of the most prominent assumptions of the US gun control debate.

Just 22% of current gun owners who acquired a firearm within the past two years did so without a background check, according to a new national survey by public health researchers at Harvard and Northeastern universities shared in advance with the Trace and the Guardian.

For years, politicians and researchers have estimated that as many as 40% of gun transfers are conducted without a background check – a statistic based on an extrapolation from a 1994 survey. Gun rights activists had decried that estimate as outdated and inaccurate.