If it rains on your friend in New York, does it make you less happy in San Diego?
The answer is “yes”, according to James Fowler, a social scientist at the University of California. Fowler and his team of researchers spent three years examining Facebook posts by more than 100 million users in the 100 most populous U.S. cities. Relying on automated text analysis, they measured the emotional content of each post and sorted the status updates by their positive or negative language.
The researchers used rainy weather as a variable to measure the effect of a change in one user’s posts on the posts of their friends, as rainy weather reliably changes the tenor of posts. To make sure that rain was not affecting the friends directly, they restricted their analysis to friends who were in different cities where it was not raining, and removed all weather-related status updates.
The researchers found that rainy days directly influenced the emotional tone of a person's Facebook posts, increasing the number of negative posts by 1.16% and decreasing positive posts by 1.19%. That, in turn, affected the Facebook status of one or two friends in other cities where it wasn't raining. Each additional positive post resulted in a further 1.75 positive posts among friends, while each negative post yielded 1.29 more negative posts by friends.
The study has widespread implications. Emotions, the researchers write, “Might ripple through social networks to generate large-scale synchrony that gives rise to clusters of happy and unhappy individuals. We may see great spikes in global emotion that could generate increased volatility in everything from political systems to financial markets.”