Americans aged over 65 are much more likely than younger people to share fake news on Facebook, researchers say.
Their study looked at the behaviour of Facebook users before and after the 2016 US presidential election.
It found age was a better predictor of whether people passed around links to sites producing untrue stories than any other characteristic.
But, it said, only 8.5% of people shared any stories generated by fake news sites.
The 3,500 people studied were recruited prior to the 2016 election and about half of them agreed to install an app that gathered information from their Facebook profile and logged what they shared.
It found that just over 11% of people aged 65 or over shared links to fake stories. By contrast, only 3% of those aged 18-29 actively passed on similar links.
"No other demographic characteristic we examined - gender, income, education - had any consistent relationship with the likelihood of sharing fake news," wrote the paper's authors in a report published in the Washington Post.
In addition, suggests the study, pro-Trump republicans were more likely (18%) to share links than those who identified as Democrats (3.5%).
The researchers, from New York University and Princeton, did not draw conclusions about why older people were more likely to direct their Facebook friends to fake news sites.
They speculated that digital illiteracy among older people stopped them spotting the signs of bogus news items or, they suggested, it could be linked to age-related cognitive decline, which made them easier to fool.
Although the numbers of links being shared were small, they could have a significant impact, said the researchers, because far more people read fake news than passed it on.
Separate research they cited suggested up to 25% of Americans read fake news stories from many different sources in the run-up to the 2016 vote.
The researchers suggested using education projects and online interventions to help people of all ages spot dodgy news stories.