NEW YORK • Fake news evolved from seedy Internet sideshow to serious electoral threat so fast that behavioural scientists had little time to answer basic questions about it.
But now the first hard data on fake-news consumption has arrived. Researchers last week posted an analysis of the browsing histories of thousands of adults during the run-up to the 2016 US presidential election - a real-time picture of who viewed which fake stories, and what real news those people were seeing at the same time.
The reach of fake news - a term which has evolved into an all-purpose smear, used by President Donald Trump and other politicians to deride journalism they do not like - was wide indeed, the study found, yet also shallow. One in four Americans saw at least one false story, but even the most eager fake-news readers - deeply conservative supporters of Mr Trump - consumed far more of the real kind, from newspaper and network websites and other digital sources.
In the new study, a trio of political scientists - Professor Brendan Nyhan of Dartmouth College, Dr Andrew Guess of Princeton University and Professor Jason Reifler of the University of Exeter - analysed Web traffic data gathered from a representative sample of 2,525 Americans who consented to have their online activity monitored anonymously by the survey and analytic firm YouGov.
The data included website visits made in the weeks before and after the 2016 election, and a measure of political partisanship based on overall browsing habits.
The team defined a visited website as fake news if it posted at least two demonstrably false stories, as defined by economists Hunt Allcott and Matthew Gentzkow. On 289 such sites, about 80 per cent of bogus articles supported Mr Trump.
The online behaviour of the participants was expected in some ways, but surprising in others. The most conservative 10 per cent of the sample accounted for 65 per cent of visits to fake news sites.
Pro-Trump users were about three times more likely to visit fake news sites supporting their candidate than partisans of Democrat Hillary Clinton were to visit bogus sites promoting her.
Still, false stories were a small fraction of the overall news diet, regardless of political preference: just 1 per cent among Mrs Clinton's supporters, and 6 per cent among those pulling for Mr Trump.
The study found that Facebook was by far the platform through which people most often navigated to a fake news site. Last year, in response to criticism, the company began flagging stories on its site that third-party fact-checkers found to make false claims with a red label saying "disputed".
There was no way to determine how much, or whether, people believed what they saw on these sites.
"For all the hype about fake news, it's important to recognise that it reached only a subset of Americans, and most of the ones it was reaching already were intense partisans," Prof Nyhan said.
Given the ratio of truth to fiction, fake news paled in influence beside mainstream news coverage, said research scientist Duncan Watts at Microsoft.