• by Erik Sass , Staff Writer @eriksass1, March 13, 2014

It might be time to reconsider whose Facebook posts you read, since it turns out that emotional states, including good and bad moods, can spread from person to person via social media, according researchers at the University of California, San Diego. And bad weather doesn’t help, either.
 
The study, titled “Detecting Emotional Contagion in Massive Social Networks” and published in the journal Plos One, analyzed around 1 billion Facebook posts by 1 million users using a system called Linguistic Inquiry and Word Count, then overlaid this sentiment with weather data showing when it was raining in a particular location.

After showing the correlation between bad weather and negative emotional states in rainy cities, they then examined how Facebook posts by users experiencing bad weather affected Facebook posts by friends in places with good weather.
 
James Fowler, a professor of medical genetics and political science at UCSD, summed up the approach for an interviewer: “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?”
 
Overall, the study found, rain increased the number of negative posts from users in a given area by 1.16%, while positive posts decreased 1.9%. More interesting, however, both good and bad moods had ripple effects online, as Facebook friends in other parts of the country responded to the posts.

On average, a negative post from a person in a rainy area triggered a 1.29% increase in negative posts by Facebook friends living elsewhere, while each positive post triggered a 1.75% increase in positive posts. Thus, a rainy day in New York results in 1,500 incremental negative posts by Facebook users living there, leading to around 700 additional negative posts by their friends in other cities.
 
These data would appear to suggest happiness is more contagious than sadness -- but anger is a whole ‘nother ball game.

Last year, I wrote about a study by researchers at Beihang University, titled “Anger is More Influential Than Joy: Sentiment Correlation on Weibo.” The research team categorized around 70 million posts from 200,000 users on Weibo, a Twitter-like platform, according to sentiment, including anger, joy, sadness and disgust. Their analysis showed that Weibo users who post angry sentiments are more likely to be connected to other Weibo users who post angry sentiments -- making anger an “assortative” factor in the organization of online networks. The researchers also found that angry Weibo users are more likely to propagate angry sentiments via their networks.