There may be a literal truth underlying the common-sense intuition that happiness and sadness are contagious.
A new study on the spread of emotions through social networks shows that these feelings circulate in patterns analogous to what’s seen from epidemiological models of disease.
Earlier studies raised the possibility, but had not mapped social networks against actual disease models.
“This is the first time this contagion has been measured in the way we think about traditional infectious disease,” said biophysicist Alison Hill of Harvard University. [...]
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.