Published 4 December 2008, doi:10.1136/bmj.a2338
Cite this as: BMJ 2008;337:a2338

Research

Dynamic spread of happiness in a large social network: longitudinal analysis over 20 years in the Framingham Heart Study

James H Fowler, associate professor1, Nicholas A Christakis, professor2

1 Department 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

Correspondence to: N A Christakis christak{at}hcp.med.harvard.edu

Objectives To evaluate whether happiness can spread from person to person and whether niches of happiness form within social networks.

Design Longitudinal social network analysis.

Setting 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.


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Rapid Responses:

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Excellent
umesh chandra
bmj.com, 6 Dec 2008 [Full text]
Personal view
Michael Tooth
bmj.com, 8 Dec 2008 [Full text]
Isn't Social Life, Then, Contagious?
Mauri O. Yambo
bmj.com, 9 Dec 2008 [Full text]
Interesting but where's the social politics?
Dr G Smith
bmj.com, 18 Dec 2008 [Full text]
A disappointing finding
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know your friends
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