Once again, research threatens to vindicate an old intuitive idea: that the emotional states of happiness and sadness can be contagious, spreading between individuals in much the same way that flu does. The bad news? It looks like sadness is far more virulent than happiness…

In the current study, Hill’s team compared patterns of relationships and emotions measured in the study to those generated by a model designed to track SARS, foot-and-mouth disease and other traditional contagions. They discounted spontaneous or immediately shared emotion — friends or relatives undergoing a common experience — and focused on emotional changes that followed changes in others.

In the spread of happiness, the researchers found clusters of “infected” and “uninfected” people, a pattern considered a “hallmark of the infectious process,” said Hill. “For happiness, clustering is what you expect from contagion rates. Whereas for sadness, the clusters were much larger than we’d expect. Something else is going on.”

Happiness proved less social than sadness. Each happy friend increased an individual’s chances of personal happiness by 11 percent, while just one sad friend was needed to double an individual’s chance of becoming unhappy.

At this point it’s worth remembering (as the researchers themselves point out) that correlation isn’t causation:

Both Hill and Rand warned that the findings illustrate broad, possible dynamics, and are not intended to guide personal decisions, such as withdrawing from friends who are having a hard time.

“The better solution is to make your sad friends happy,” said Rand.

Amen to that.