The stories highlighted in Facebook's Trending Topics section are determined by an algorithm, but also influenced by human editors, documents leaked to The Guardian reveal.
They "Trending Review Guidelines" show that while Facebook's algorithm allows news stories to surface, its editors are tasked with determining the level of importance.
For a trend to achieve "national story" status, for instance, Facebook guidelines required it be the leading story on at least five of the following 10 news websites: BBC News, CNN, Fox News, The Guardian, NBC News, The New York Times, USA Today, The Wall Street Journal, Washington Post and BuzzFeed News. As The Guardian noted, most conservatives would say the majority of those sources lean liberal.
The documents also provided guidelines for editors to "inject" and "blacklist" topics.
Such guidelines prevented the team from injecting a story that was "not appearing in the demo or review tools." Moreover, the rules said blacklisting should only be used to eliminate duplicate topics or if the trend "doesn't represent a real-world event." Facebook explained the rule was often used for trends like "#lunch" which are talked about each day, but aren't tied to a news event.
In a blog post, Facebook Vice President Justin Osofsky again pushed back against allegations that "reviewers have been instructed by Facebook to inject specific stories into Trending Topics to suppress conservative news/sites."
"No — and the guidelines do not permit reviewers to add or suppress political perspectives," he wrote.
Osofsky noted that the blacklist guidelines "do not permit the suppression of political perspectives" and insisted the "tool is not used to suppress or remove articles or topics from a particular perspective."
He concluded his note saying that Facebook continued to investigate the allegations made in the Gizmodo report.
"We take these reports very seriously, and will continue to investigate the allegations. We have found no evidence to date that Trending Topics was successfully manipulated, but will continue the review of all our practices," he wrote.
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