Facebook posts are 'contagious,' researchers find

That bad mood you're in isn't just a downer for those around you; it spreads to your friends in other cities via cyberspace. And if you're happy, you've boosted their mood and likely others' as well, according to new research that suggests that real-life emotions also can spread online.

The study, published Wednesday in the online journal PLOS ONE, analyzed more than a billion anonymous status updates among more than 100 million Facebook users across the USA and found a "multiplier effect on our emotions."

"This is a new way for emotions to spread that didn't exist before," says senior author James Fowler, a social scientist at the University of California, San Diego, who has spent years studying emotions and behaviors and how contagious they are.

A team of researchers analyzed Facebook status updates in the top 100 largest U.S. cities between January 2009 and March 2012, looking at between-city friendships rather than those in the same town. They used rain as a measurement tool – employed previously by researchers because it's a random element that can't be influenced by human emotion -- to see how friends exposed to rain influenced those who weren't.

"If it rains on your friend in New York, does it make you less happy in San Diego? The answer is 'yes,' " Fowler says.

Negative posts spawn negative posts, and positive posts generate positive ones, with positive ones more likely to spread, he says.

"Each happy post causes your friends in other cities to write an additional one to two happy posts," Fowler says.

Now, "we can make stronger claims that one person's emotions are influencing another person's emotions," Fowler says.

Keith Hampton, an associate professor of communication at Rutgers University in New Brunswick, N.J., who was not involved in the study, says the research provides "more solid confirmatory evidence" rather than the "modest evidence" of the past that emotions are contagious through social media.

"I'm not aware of any other studies that have done such a rigorous job," Hampton says. "This study is significant for showing there is a contagion of emotions on social media."

The researchers relied on automated text analysis, through a software program that allowed them to measure the emotional content of each post. They did not see names of users or the words posted.

In addition to UC-San Diego, the co-authors include researchers from Yale University in New Haven, Conn. and Facebook in Menlo Park, Calif. Fowler says he's an unpaid contractor with Facebook whose agreement allows him access to data for research, which is similar to arrangements with other university researchers.

"These results suggest that online social networks are a force for increasing happiness," he says. "Every post you write that's happy causes another person to write one or two more posts that's happy. That's a doubling to tripling of one emotional experience."