Emotions on Facebook are contagious, according to a new study, with positive posts spurring more positive posts and negative posts spurring more negative posts.
In addition, positive posts on social media seem to be more "contagious" than negative ones, the PLOS ONE study showed.
To come to this conclusion, researchers from the University of California, San Diego, analyzed Facebook updates from the 100 most populous U.S. cities that were posted between January 2009 and March 2012. Emotional content of the updates was determined with a program called Linguistic Inquiry Word Count.
Researchers looked specifically at how rainy weather -- which they knew increased negative Facebook updates by 1.16 percent and decreased positive Facebook updates by 1.19 percent -- affected emotional content of friends' posts, particularly friends who weren't living in cities where it was raining.
"For our analysis, to get away from measuring the effect of the rain itself, we had to exclude the effects of posts on friends who live in the same cities," study researcher James Fowler, professor of political science in the Division of Social Sciences and of medical genetics in the School of Medicine at UC San Diego, said in a statement.
Researchers also purposely didn't include status updates that were weather-related, in order to make sure it wasn't just the topic of weather that was being spread.
They found that the negative posts yielded 1.29 additional negative posts from friends, while positive posts yielded 1.75 additional positive posts from friends.
"If it rains on your friend in New York, does it make you less happy in San Diego? The answer is 'yes,'" Fowler told USA Today.
The LA Times pointed out that Fowler has done previous work showing that obesity can even be "contagious," though experts have criticized that work, calling it "not convincing."