University of California, San Diego (UCSD) researchers analyzed more than a billion anonymized status updates among more than 100 million Facebook users in the United States and found that positive posts encouraged positive posts and negative posts produced negative ones, with the positive posts being more influential, or more contagious. "Our study suggests that people are not just choosing other people like themselves to associate with but actually causing their friends' emotional expressions to change," says UCSD professor James Fowler. "We have enough power in this data set to show that emotional expressions spread online and also that positive expressions spread more than negative." Each additional negative post yields 1.29 more negative posts among a person's friends, while each additional positive post yields an additional 1.75 positive posts among friends, according to the study. To read further, please visit http://ucsdnews.ucsd.edu/pressrelease/facebook_feelings_are_contagious_study_shows.