www.bbc.com/news/technology-28102550

According to the report on the study: "The experiment manipulated the extent to which people were exposed to emotional expressions in their News Feed".
The study found that users who had fewer negative stories in their news feed were less likely to write a negative post, and vice versa.



In an alternate study it was found that users who discovered they were part of a study without their consent posted a lot of negative posts.
:-)