Last month, Dr. James Fowler (UCSD) and Dr. Nicholas Christakis (Harvard University) published a research paper evaluating the spread of happiness within social networks. Their findings? Happiness is contagious up to three degrees of separation [doi:10.1136/bmj.a2338].

The following is an excerpt from an article written by the authors of the aforementioned paper:

By Nicholas A. Christakis & James H. Fowler

…Our happiness is determined by a complex set of voluntary and involuntary factors, ranging from our genes to our health to our wealth. Alas, one determinant of our own happiness that has not received the attention it deserves is the happiness of others. Yet we know that emotions can spread over short periods of time from person to person, in a process known as “emotional contagion.” If someone smiles at you, it is instinctive to smile back. If your partner or roommate is depressed, it is common for you to become depressed.

But might emotions spread more widely than this in social networks—from person to person to person, and beyond? Might an individual’s location within a social network influence their future happiness? And might social network processes—by a diverse set of mechanisms—influence happiness not just fleetingly, but also over longer periods of time? 

We recently published a paper in the British Medical Journal that addressed these questions. We studied 4,739 people followed from 1983 to 2003 as part of the famous Framingham Heart Study. These individuals were embedded in a larger network of 12,067 people; they had an average of 11 connections to others in the social network (including to friends, family, co-workers, and neighbors); and their happiness was assessed every few years using a standard measure. 

We found that social networks have clusters of happy and unhappy people within them that reach out to three degrees of separation. A person’s happiness is related to the happiness of their friends, their friends’ friends, and their friends’ friends’ friends—that is, to people well beyond their social horizon. We found that happy people tend to be located in the center of their social networks and to be located in large clusters of other happy people. And we found that each additional happy friend increases a person’s probability of being happy by about 9%. For comparison, having an extra $5,000 in income (in 1984 dollars) increased the probability of being happy by about 2%.

Happiness, in short, is not merely a function of personal experience, but also is a property of groups. Emotions are a collective phenomenon…

I’m infectious! :)