Facebook pages for local Republican Party groups saw greater engagement over local Democratic Party pages as news of a Facebook algorithm change came to light in 2018, according to new research.

The research, shared on Wednesday in Research & Politics, details a gap in engagement growth “unique to Facebook” between the GOP pages and their Democratic counterparts by 2019.

The growth included a “doubling of the total shares” of local GOP parties’ posts to their pages compared with Democratic posts ― posts that occurred more often ― on their pages in the first half of 2019, the research said.

“Regardless of Facebook’s motivations, their decision to change the algorithm might have given local Republican parties greater reach to connect with citizens and shape political realities for Americans,” the research authors noted in their abstract.

“The fact that private companies can so easily control the political information flow for millions of Americans raises clear questions for the state of democracy.”