Objectives To evaluate whether happiness can spread from person to person and whether niches of happiness form within social networks. Framingham Heart Study social network. Participants 4739 individuals followed from 1983 to 2003. Main outcome measures Happiness measured with validated four item scale; broad array of attributes of social networks and diverse social ties.
Results Clusters of happy and unhappy people are visible in the network, and the relationship between people’s happiness extends up to three degrees of separation (for example, to the friends of one’s friends’ friends).
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.
Conclusions People’s happiness depends on the happiness of others with whom they are connected. This provides further justification for seeing happiness, like health, as a collective phenomenon.
Happiness is a fundamental object of human existence, so much so that the World Health Organization is increasingly emphasising happiness as a component of health.
Happiness is determined by a complex set of voluntary and involuntary factors. Researchers in medicine, economics, psychology, neuroscience and evolutionary biology have identified a broad range of stimuli to happiness (or unhappiness), including lottery wins, elections, income, job loss, socioeconomic inequality, divorce, illness, bereavement and genes.
These studies, however, have not addressed a possibly key determinant of human happiness: the happiness of others.
Emotional states can be transferred directly from one individual to another by mimicry and “emotional contagion,” perhaps by the copying of emotionally relevant bodily actions, particularly facial expressions, seen in others.
People can “catch” emotional states they observe in others over time frames ranging from seconds to weeks. For example, students randomly assigned to a mildly depressed room-mate became increasingly depressed over a three month period, and the possibility of emotional contagion between strangers, even those in ephemeral contact, has been documented by the effects of “service with a smile” on customer satisfaction and tipping.
Yet, despite the evidence that certain emotions might spread over short periods from person to person, little is known about the role of social networks in happiness or about whether happiness might spread, by a diverse set of mechanisms, over longer periods or more widely in social networks.
As diverse phenomena can spread in social networks, we investigated whether happiness also does so. We were particularly interested in whether the spread of happiness pertains not just to direct relationships (such as friends) but also to indirect relationships (such as friends of friends) and whether there are geographical or temporal constraints on the spread of happiness through a social network.
The Framingham Heart Study was initiated in 1948, when 5209 people in Framingham, Massachusetts, were enrolled into the “original cohort.”
In 1971, the “offspring cohort,” composed of most of the children of the original cohort, and their spouses, was enrolled. This cohort of 5124 people has had almost no loss to follow-up other than death (only 10 people dropped out).
Enrolment of the so called “third generation cohort,” consisting of 4095 children of the offspring cohort, began in 2002. The Framingham Heart Study also involves certain other smaller cohorts (such as a minority over-sample called the OMNI cohort, enrolled in 1995).
At regular intervals participants in all these cohorts come to a central facility for detailed examinations and collection of survey data.
We used the offspring cohort as the source of 5124 key individuals to study—whom we term “egos.” Each ego in this cohort is connected to other people via friendship, family, spousal, neighbour, and coworker relationships. Each relationship is a “social tie.”
Each person who has a relationship with an ego was called an “alter.” For example, one ego in the offspring cohort had 18 alters: a mother, a father, a sister, two brothers, three children, two friends, five neighbours, and three coworkers. We wanted to know how each of these alters influences an ego.
Many of the alters also happened to be members of a studied cohort in Framingham, which means that we had access to detailed information about them as well.
Overall, within the entire Framingham Heart Study social network, composed of both the egos and any detected alters in any Framingham Heart Study cohort, there were 12 067 individuals who were connected at some point in 1971-2003.
James H Fowler1, associate professor, Nicholas A Christakis, professor
1Department of Political Science, University of California, San Diego, CA, USA , 2 Department of Health Care Policy, Harvard Medical School, and Department of Sociology, Harvard University, Cambridge, MA, USA