Scientists at Facebook changed hundreds of thousands of users’ “news feeds” to see if reading more negative or positive content could affect their moods.

“For people who had positive content reduced in their News Feed, a larger percentage of words in people’s status updates were negative and a smaller percentage were positive. When negativity was reduced, the opposite pattern occurred.”…

Read more:

http://www.smh.com.au/digital-life/digital-life-news/emotional-states-on-facebook-contagious-research-finds-20140628-zsp8m.html