Facebook on Monday said it was making changes aimed at keeping political bias out of its "trending" stories list even though an internal investigation revealed no evidence it was happening.
"Our investigation has revealed no evidence of systematic political bias in the selection or prominence of stories included in the Trending Topics feature," Facebook general counsel Colin Stretch said in a letter responding to a query from Republican US Senator John Thune, who chairs the commerce committee.
"In fact, our analysis indicated that the rates of approval of conservative and liberal topics are virtually identical in Trending Topics."
Facebook was unable to substantiate any specific accusations of bias made in media reports, which relied on anonymous sources, Stretch said in the letter, a copy of which was made available by the leading social network.
"At the same time, as you would expect with an inquiry of this nature, our investigation could not exclude the possibility of isolated improper actions or unintentional bias in the implementation of our guidelines or policies," Stretch said.
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"As part of our commitment to continually improve our products and to minimize risks where human judgment is involved, we are making a number of changes."
Facebook updated terminology in its guidelines to be clearer and gave reviewers refresher training that emphasized content decisions may not be based on politics or ideology, the letter said.
The review team will be subject to more oversight and controls, and Facebook will no longer rely on lists of external websites and news outlets to assess the importance of topics in stories.
"We want people to be confident that our community welcomes all viewpoints," Stretch said in the letter.
Facebook founder Mark Zuckerberg said last week that conservatives are an important part of the social network after a meeting aimed at defusing concerns it is politically biased.
"We've built Facebook to be a platform for all ideas," Zuckerberg said on his Facebook page after a meeting at the company's California headquarters to discuss the allegations about anti-conservative bias.
"It doesn't make sense for our mission or our business to suppress political content or prevent anyone from seeing what matters most to them."
Zuckerberg called the meeting after technology news outlet Gizmodo a week earlier reported allegations that Facebook was deliberately omitting articles with conservative viewpoints from the sidebar that lists popular stories.
"Very productive meeting at @Facebook with Mark and team," CNN conservative commentator S.E. Cupp tweeted after attending the gathering. "Strong commitments to address issues, as well as to work together on common goals."