We already know that cat memes and BuzzFeed lists spread around Facebook quicker than germs in a kindergarten classroom. But can emotions go viral as well?
Perhaps, researchers say. When your Facebook friends post happy things online, you're more likely to do so too, according to a study published Wednesday. And the same applies for negative posts: If your friends are being grumpy online, you're more likely to post something negative.
Researchers from the University of California, San Diego, analyzed millions of Facebook posts over the course of three years. To gauge how moods traveled across social networks, the researchers looked at the example of rain.
"We were literally trying to answer the question: If it rains on your friend in Los Angeles, does it make you a little less happy in New York?" says James Fowler, the lead researcher and a professor of medical genetics and political science at UCSD.
After controlling for things like the average weather in a Facebook user's city, the researchers found that a rainy day increased the number of negative posts that users published on Facebook by a little more than 1 percent.
It's a small change, Fowler tells Shots. But the researchers also found that each sad status posted on a rainy day gave rise to another negative post by a friend living in a city that was dry. Positive moods seemed even more contagious each happy post typically yielded two additional happy posts by others. The scientists detailed their findings in the current issue of the journal PLOS ONE.
To measure how positive or negative the posts were, the researchers used a word classification system called the Linguistic Inquiry and Word Count.
Rain seemed like a good variable because it's essentially random it tends to fall on happy and sad people in equal measure. Most studies that show a correlation between social interaction and mood can't prove that one causes the other, Fowler says. Positive people, for example, might simply choose to associate with other positive people, and grumpy people might befriend other grumpy people.
But this study, he says, found that even a single, isolated rainy day could affect a person's mood and that mood could be contagious online.
Of course, the research only looked at how rain affected the general tenor of Facebook posts. And the effect was fairly small. Fowler says the next step is to look at how specific emotions spread across social networks. He says it's likely the study underestimates how emotion spreads online, since a bit of bad weather isn't the worst that can happen.
But the takeaway here, Fowler says, is that social media's influence on mood isn't all bad, despite studies that show young people can pick up bad habits online and that social media use can make us feel sad.
You can spread happiness online as well, Fowler says: "While it's true that there are always people out there who might influence our mood, we also have the capacity to influence other people's mood."
That's something to consider before posting your next rant about this winter's horrid weather.
Copyright 2014 NPR. To see more, visit http://www.npr.org/.