YouTube Cut Down Misinformation. Then It Boosted Fox News.

A Fox News spokesperson said the network had worked hard to elevate its presence on YouTube. Fox News created a team focused on the platform and has made a point of posting videos that perform well with YouTube’s search engine and with viewers, such as live broadcasts of breaking news.

On Facebook, Fox News’s page accounted for 10 percent of all interactions with posts about the election over the past week, according to CrowdTangle. That was second only to President Trump’s official page, at 18 percent, and above Breitbart’s at 6 percent.

The next major network was CNN at 2 percent, roughly on a par with the page of “Fox & Friends,” the Fox News morning show. Facebook declined to comment but noted that interactions do not entirely reflect a post’s reach, though they are the only measure of a post’s popularity that the company makes available.

In one analysis, Mr. Chaslot and Mr. Faddoul collected recommendations daily on videos posted by 800 of YouTube’s most popular news-related channels over the three weeks that ended on Oct. 27. Fox News accounted for more than 3 percent of the 300,000 recommendations collected, more than twice the rate of the next-closest channel, the History Channel. CNN and MSNBC accounted for about 1 percent of recommendations.

When the researchers analyzed only videos about the election from the same channels, Fox News accounted for 10 percent of all the recommendations, nearly three times the rate of the No. 2 most-promoted channel, MSNBC. Other analyses of recommendations alongside some of the most popular election-related videos also showed Fox News as the most-promoted channel.

Given the enormous size and influence of social networks like YouTube and Facebook, changes to how they promote content often causes unforeseen outcomes, such as news organizations writing headlines or framing stories to please the new algorithms, said Arvind Narayanan, a computer scientist at Princeton University who studies the effect of algorithms on society.

“YouTube is constantly tinkering with its algorithms,” he said. “And when it does that, it always is going to have both intended and unintended effects.”