Happiness is contagious and friendship is magic: That's the lesson from a 20-year multi-generational study, which concludes that people's happiness depends on the happiness of those we're connected with.
Of the types of relationships and social ties that spread happiness, the Framingham Heart Study, which tracked individuals from 1983 to 2003, found that mutual friends living within a mile of each other and next door neighbours influenced happiness the most:
People who are surrounded by many happy people and those who are central in the network are more likely to become happy in the future. Longitudinal statistical models suggest that clusters of happiness result from the spread of happiness and not just a tendency for people to associate with similar individuals. A friend who lives within a mile (about 1.6 km) and who becomes happy increases the probability that a person is happy by 25% (95% confidence interval 1% to 57%). Similar effects are seen in coresident spouses (8%, 0.2% to 16%), siblings who live within a mile (14%, 1% to 28%), and next door neighbours (34%, 7% to 70%). Effects are not seen between coworkers. The effect decays with time and with geographical separation.
It's hard to make friends as you get older, but worth the effort to make and maintain your friendships -- especially if your friends live nearby.