Cheering news in gloomy times. New research from James Fowler of UC San Diego and Nicholas Christakis of Harvard Medical School shows that happiness can spread from person to person to person in a chain reaction through social networks. ‘One of the key determinants of human happiness is the happiness of others,’ said Christakis. ‘An innovative feature of our work was exploring the idea that emotions are a collective phenomenon and not just an individual one.’
Christakis and Fowler used data from the Framingham Heart Study to recreate a social network of 4,739 people whose happiness was measured from 1983 to 2003. To assess the participants' emotional wellbeing, they relied on answers to four questions: ‘I felt hopeful about the future’; ‘I was happy’; ‘I enjoyed life’; and ‘I felt that I was just as good as other people’.

The research shows that happy people tend to cluster together, and what matters is the total number of happy connections. On average, every happy friend increases your own chance of being happy by 9%. Each unhappy friend decreases it by 7%.

Happiness, it appears, spreads in a social network up to three degrees of separation. You are 15% more likely to be happy if directly connected to a happy person; 10% if it's the friend of a friend who is happy; and 6% if it's the friend of a friend of a friend. Unhappiness also spreads, but not nearly as much. To get this in perspective, in 1984 an extra $5,000 (a lot of money then) was associated with just a 2% rise in happiness – compared with a 6% rise for a friend of a friend of a friend being happy!

The structure of connections matters, too. According to the study, individuals' happiness depends not only on how many friends they have but also on how many friends their friends have. In social network terms, this is known as ‘centrality’. And the more central a person is, the better connected their friends, or the wider the social circle the more likely they are to become happy. (The effect does not work the other way around: becoming happy doesn't widen a social circle.)
Fowler and Christakis also looked at what happens to happiness with distance. When a friend (or sibling) who lives within a mile becomes happy, it increases the probability a person is happy by 25%. More distant friends have no significant effect. Next-door neighbours have a significant effect, 34%, while neighbours further away, even on the same block, do not. They believe that physical personal interaction is necessary, so the effect decays both with distance and with time.
There are several practical implications to the work, not least of which might be to take greater responsibility for your own happiness because it affects dozens of others.

The study appeared in the British Medical Journal in December

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03/09

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