FILE - A Facebook employee walks past a sign at Facebook headquarters in Menlo Park, California, March 15, 2013.
FILE - A Facebook employee walks past a sign at Facebook headquarters in Menlo Park, California, March 15, 2013.

WASHINGTON - Republican U.S. Senator John Thune says Facebook has been "forthcoming" about how it determines what appears in its Trending Topics section, and adds that he appreciates the company's efforts to address allegations of bias against conservative viewpoints.

Thune asked the company to answer questions about its practices after reports cited a former Facebook employee saying contractors on the Trending Topics team routinely suppressed stories that would interest conservative users.

He said if the allegations were true, then Facebook was misleading the public in its claim to be a platform for people and perspectives from across the political spectrum.

The company responded Monday with a 12-page letter from Facebook General Counsel Colin Stretch who said an internal review found no evidence of systemic political bias in either the selection or prominence of stories.

"In fact, our analysis indicated that the rates of approval of conservative and liberal topics are virtually identical in Trending Topics," Stretch said.  But he did not exclude the possibility that since the feature launched in 2014 there have been "isolated improper actions or unintentional bias."

The letter addressed some of the specific allegations, including that Facebook suppressed news about Republicans Ted Cruz, Rand Paul, Mitt Romney and Scott Walker.  The company said its probe did not substantiate the claims, and that stories about each figure appeared as trending topics dozens of times.

"Two of the most frequently accepted topics since early 2015 are presumptive Republican presidential nominee Donald Trump and #GOPDebate," Stretch said.

Thune, who chairs the Senate's Committee on Commerce, Science and Transportation, said after receiving the letter he looks forward to Facebook's actions meeting its public statements.

FILE - Sen. John Thune, R-S.D. addresses the media
FILE - Sen. John Thune, R-S.D. addresses the media.

"Facebook has recognized the limitations of efforts to keep information systems fully free from potential bias, which lends credibility to its findings," Thune said.  "While the committee remains open to new information on this matter, transparency -- not regulation -- remains the goal, so I thank the company for its efforts to acknowledge relevant facts and its recognition of a continuing need to transparently address relevant user questions."

The Trending Topics section appears in the upper right corner on the website version of Facebook.  The company says its 1.6 billion users get different content there based on a computer algorithm that has certain limitations, requiring a team of humans to take steps such as weeding out duplicate and nonsensical topics and writing descriptions.

Stretch said as many as half of the topics identified by the algorithm are thrown out by reviewers who also have the ability to sideline certain topics for a short time in order to let better sources develop or for the reason a word or phrase is trending to become more clear.  He gave as an example the hashtag #lunch that surges in use in the middle of every day but is not a meaningfully trending topic.

The system in part relied on looking at a number of prominent news sources and "boosting" those items that were leading the coverage across a number of sites.  Facebook says ending that practice is among the changes it is making following its review.  Others include updating terminology in its guidelines and giving refresher training to employees reminding them that their decisions about content cannot be based on ideology or politics.

"We want people to feel confident that our community welcomes all viewpoints and we are committed to designing our products to give all people a voice and foster the free flow of ideas and culture," Stretch said.