BERLIN, GERMANY - FEBRUARY 24: The Facebook logo is displayed at the Facebook Innovation Hub on February 24, 2016 in Berlin, Germany. The Facebook Innovation Hub is a temporary exhibition space where the company is showcasing some of its newest technologies and projects. (Photo by Sean Gallup/Getty Images)
Facebook said its "news curators" didn't suppress conservative news outlets in its trending news module, even though they have the capability to do so.
Tom Stocky, who is in charge of Facebook's trending topics team, said that after an algorithm picks out popular topics for the module, humans audit the results. During that review process, bias can easily seep into what's considered top news.
But the top news module is small and found on mobile devices only after a search. Some say it would be of more concern if Facebook used personal bias to curate users' main news feeds, which could happen.
In 2014, Facebook admitted to tweaking the news feed, or at least to letting researchers experiment with the feed.