Emotions spread through a social group in ways that resemble the spread of disease. According to a study performed in Massachusetts, sadness is more contagious than happiness. "'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...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.'"