But that figure is based on an analysis of a nearly two-decade-old survey of less than 300 people that essentially asked participants whether they thought the guns they had acquired — and not necessarily purchased — came from a federally licensed dealer. And one of the authors of the report often cited as a source for the claim — Philip Cook of Duke University — told our friends at Politifact.com that
he has "no idea" whether the "very old number" applies today or not. Even Vice President Joe
Biden acknowledged that the statistic may not be accurate in a speech at a mayoral conference on Jan. 17. Biden prefaced his claim that "about 40 percent of the people who buy guns today do so outside the … background check system" by saying that "
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."
...
Both of those statements were based on a single 1994 telephone survey on private gun ownership conducted by the Police Foundation and funded by the Justice Department. The survey asked the 251 participants who had acquired guns in the previous two years, "Was the person you acquired this gun from a licensed firearm dealer?" The answer choices were "yes," "probably was/think so," "probably not," "no/definitely not," "don't know" and refuse to report. Cook and Ludwig
found that 64.3 percent of those surveyed (Table 3.14) said that they had purchased or traded for a gun that came from a licensed dealer or "probably" did. The 40 percent figure comes from
assuming that the remaining 35.7 percent — which has been rounded up — did not.