According to 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 companys 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. 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% and 90% 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 friends timeline directly or reloading the News Feed.