According to a new paper in the Proceedings of the National Academy of Science, Facebook altered the News Feeds for hundreds of thousands of users as part of a psychology experiment devised by the company's on-staff data scientist. By scientifically altering News Feeds, the experiment sought to learn about the way positive and negative effect travels through social networks, ultimately concluding that "in-person interaction and nonverbal cues are not strictly necessary for emotional contagion."
"Each emotional post had between a 10 percent and 90 percent chance...of being omitted."
To test the hypothesis, the researchers identified 689,003 different English-language Facebook users, and began removing emotionally negative posts for one group and positive posts for another. According to the paper, "when a person loaded their News Feed, posts that contained emotional content of the relevant emotional valence, each emotional post had between a 10 percent and 90 percent chance (based on their User ID) of being omitted from their News Feed for that specific viewing." The posts were still available by visiting a friend's timeline directly or reloading the News Feed. The researchers also state that they did not alter any direct messages sent between users.