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

BMJ 2008; 337 doi: (Published 05 December 2008) Cite this as: BMJ 2008;337:a2338
  1. James H Fowler, associate professor1,
  2. Nicholas A Christakis, professor2
  1. 1Department of Political Science, University of California, San Diego, CA, USA
  2. 2Department of Health Care Policy, Harvard Medical School, and Department of Sociology, Harvard University, Cambridge, MA, USA
  1. Correspondence to: N A Christakis christak{at}
  • Accepted 10 September 2008


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.


  • We thank Laurie Meneades, Rebecca Joyce, Molly Collins, Marian Bellwood, and Karen Mutalik for the expert assistance required to build the analytical data. We thank Chris Dawes, Dan Gilbert, Tom Keegan, Erez Lieberman, Andrew Oswald, Mark Pachucki, and Holly Shakya for helpful suggestions regarding the manuscript.

  • Contributors: Both authors participated in the conception and design of the study, analysis and interpretation of data, drafting and revising the article, and its final approval. Both authors are guarantors.

  • Funding: This was work was supported by NIH (R-01 AG24448, P-01 AG031093) and by the Pioneer Portfolio of the Robert Wood Johnson Foundation; NHLBI’s Framingham Heart Study is supported by contract number N01-HC-25195. Neither author has a dependent relationship with any of the funding agencies.

  • Competing interests: None declared.

  • Ethical approval: This work was approved by the Harvard institutional review board; the parent Framingham Heart Study has separate IRB approval. All participants gave informed consent.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

View Full Text