New study: Happiness is a disease
Well, not really, but a recently-completed 20 year longitudinal study published in BMJ, a British medical journal, suggests that happiness is contagious. After following thousands of people for years, they found that happy people cluster together - and the data suggest that these clusters are not merely happy people choosing others like themselves. The researchers discovered that happiness spreads for up to "three degrees of separation" - to the friends of one's friends' friends. Similar contagion has been found for smoking and obesity. Because the study was conducted over time, it showed that if a friend living within a mile of someone increases that person's chance of being happy by 25%! Similar effects were seen for happy spouses, siblings living within a mile, and next-door neighbours, but not for coworkers. You can read more here - the entire article is online as I write this, including graphics of their social network data.