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

BMJ 2008; 337 doi: http://dx.doi.org/10.1136/bmj.a2338 (Published 5 December 2008)
Cite this as: BMJ 2008;337:a2338

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30 October 2009

In the words of Buddhist philosopher, Dr Daisaku Ikeda,'Happiness does not exist as an isolated quality, nor does it conform to a single fixed pattern.'

I applaud the authors for taking the brave pill and challenging current scientific parochalism. Despite the study's complexity and shortcomings (which research doesn't?), it sheds important light on human behaviour. I have observed the 'responses' to this paper, both in print and in daily life, and they range from 'should we only associate with happy people', 'should we ditch our moaning friends', 'are some people sources of misery', 'what makes people happy', 'this will marginalise unhappy people' etc.

However, the fact of the matter is that the authors and their findings claim no such thing! What is clear from the study, is that happiness is a dynamic phenomenon, and that happy people form clusters and these clusters of happiness can influence others. Although, I am not a sociologist, this seems rather positive and uplifting.

As to how happiness was assessed in this study, the two crucial components of 'hope' and 'joy' were ascertained. It is important not to mistake rapture for happiness. In that sense, humanity despite its struggles with illness, war, poverty and myriad other sociopolitical tragedies, can still generate and spread happiness.

Lastly, as an ex-researcher myself, it is heartening to see something positive come out of the Framingham Heart Study, after decades of cardiovascular anxiety, food fundamentalism and exercise gurus.

Competing interests: None declared

Competing interests: None declared

Sriram Vaidyanathan, Specialist Registrar Radiology

Southern General Hospital, Glasgow, G51 4TF

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I am glad to see that innovative researchers are extending boundaries and challenging the status quo. While acknowledge there are some shortcomings to the research, I believe these are adequately addressed.

I must say that as a rule of thumb I for many years have made a point of associating with happy people. I beleive that in the process I have 'learnt' to be happy. Here is a selection issue to consider in the construction of the network.

Obviously happiness is a two way street - it comes from within and without - and the happiness of our friends and family is one component.

Fantastic article. I wonder whether this type of analysis can be linked to findings in 'happiness economics' that have shown that after 'happiness shocks' people tend to return to a constant state of happiness. Are new happy friends a happiness shock?

Competing interests: None declared

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Cameron K Murray, Economist

Queensland, Australia

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We saw a similar, albiet more acute, impact of happiness following Hurricane Katrina when we were working in the Medical Triage Unit located at the New Orleans Convention Center. I've previously described Augie's story (read more and see his picture) and the impact that that he had on all of us. He was the type of person that smiled with his entire body. When he smiled, everyone within a 10 foot radius smiled with him. He had lost all his belongings other than three garbage bags and six blankets. Despite having nothing, he gave us something of immeasurable worth: happiness and love.

In these days of both economic and healthcare challenge it will do us well to remember that we, as individuals, have the possibility to impact the system at large. What type of a legacy will you leave?

Dan Diamond, MD
Director, Katrina Medcial Triage Unit New Orleans Convention Center
CEO, Powerdyme™

Competing interests: None declared

Competing interests: None declared

Daniel E. Diamond, Physician, CEO/Powerdyme


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24 January 2009

Fowler & Christakis report that people given a questionnaire (see footnote) to assess their ‘happiness’ tend to have similar scores to their family, neighbours and friends. As the authors freely acknowledge, this is not very surprising, since relations and friends share similar circumstances. However, Fowler & Christakis carry out further analysis to support their conjecture that there is an actual causal relation involved in the association, not merely a correlation. They are sure enough about their conclusion to conclude that their findings have ‘relevance for public health’, a serious and important claim. Have they made their case?

There seem to me to be three main arguments. The first is that the survey was taken at several points in time, allowing a longitudinal analysis. This meant that the changes in ‘happiness’ of a target individual (the ‘ego’) could be analysed, in an attempt to see if changes could be related to the present and past state of ‘happiness’ in the related individual (the ‘alter’). The key data presented in their Fig 4 show that if a ‘alter’ changes in state from unhappy to happy, this increases the probability that the ‘ego’ will be happier in the second survey. The probability increase is 0.25 if the ego and alter are friends living nearby, but close to zero if they are living far way. This is an impressive figure, but I could not see from the arguments advanced why this could not mean that nearby friends tended to share changes in fortune, particularly since far-away friends included those that had left the town.

The authors try to address this point by pointing out that the effect is much stronger between strong, mutual, friends than between asymmetrical pairs in which one names the other as a friend, but the object of their affection does not reciprocate. The authors state that ‘..if some third factor were explaining both ego and happiness, it should not respect the directionality of the tie.’ This reasoning is hard to follow. If the ‘third factor’ or hidden variable were more highly correlated between mutual friends than between more distant ones, as one would expect, the findings are exactly what one would see. It needs to be demonstrated that mutual friends do not have closer socio-economic ties than those in which the friendship is presumably much weaker.

The third argument is related to the last. The effects of an alter’s happiness are found to be much increased if they live next door rather than in the same block (presumably in the US sense of that term). The authors argue that this demonstrates a direct contagion, rather than the influence of a hidden variable. They state that ‘…socioeconomic status probably cannot explain the clustering of happy people as next door neighbours'. The key word here is ‘probably’. This is a simple question of spatial scale, which should be addressed by evidence, not conjecture. One has to assume, of course, that next door neighbours did not get together to answer the questionnaire together over a few beers.

A key issue is assortative mating (http://en.wikipedia.org/wiki/Assortative_mating), which the authors dub ‘homophily’. Happy people may choose happy friends, or as the adage has it ‘misery seeks company’. The authors state that ‘Alter’s happiness in the previous exam helps to control for homophily.’ This is a promising line, but it is not pursued: the word does not appear again in the article, and in the supplementary notes only to say that the differential analysis controls for baseline states, and thus for homophily, a rather opaque statement. A simple version of the assortative mating hypothesis would that ego and alter happiness just after they form their friendship should be more related than a few years later, supposing the friendship to have survived. The contagion theory says that the relation should be equal. It would be interesting to know the facts.

Aldous Huxley said wittily that ‘several excuses are always less convincing than one’. The same is true in Science. An accumulation of individually weak arguments makes only another weak argument. I did not find a single one of Fowler & Christakis’ arguments individually compelling. The fact that there are several might mean that they share a common defect. This would not matter if they had presented their argument in the traditional scientific way as a conjecture, consistent with the evidence but not tested by it. Instead, their conclusions state that ‘People’s happiness depends on the happiness of others with who they are connected’. They go further. Since, they say, happiness has a causal role to play in health (another unproven conjecture), it follows that their findings have relevance for public health. Presumably, the idea is that if we wish to increase someone’s happiness, and thus their health, we should be trying to make their friends happier.

They go even further, into the realms of abstract philosophy. ‘Human happiness’ they state, ‘ is not merely the province of isolated individuals.’ We seem here to be entering Durkheim territory, where suicidal impulses, rather than coming from individual brains, hover like a shroud over a society. Durkheim’s hypothesis has been thoroughly discredited in the case of suicide, so why should we now want to rescusistate it for ‘happiness?’ Even if the author’s causal hypothesis were true, it would still not rule out happiness being an individual brain state.

The real purpose of these conjectures becomes clear in the final paragraph, when the authors say that their conclusion (the causal effect of inter-personal happiness on health) ‘provides a conceptual justification for the speciality of public health’. I take it that this is a plea for resources to be diverted. The plea has my sympathy, but it does not belong in a scientific article. As President Obama has recently and eloquently said:

‘Promoting science is about ensuring that facts and evidence are never twisted or obscured by politics and ideology’. (Quoted in FT Editorial, Jan 17 2009).


Happiness is never really defined in the paper, and is certainly not measured by anything other than self-report, with all the weakness that such a measure implies. The questionnaire is described as being validated, but it would be useful to know if the validation extends beyond its predicting depression.

Competing interests: None declared

Competing interests: None declared

Michael J Morgan, Professor of Visual Neuroscience

Applied Vision Research Centre, City University London

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27 December 2008

The findings of Fowler and Christakis (1), that happiness appears to spread through social networks, are an innovative use of the Framingham Heart Study data. However, the question still remains to what extent apparent contagion of happiness to second degrees of separation could in fact be accounted for by individuals not included in the Framingham study. The original cohort consisted of only two-thirds of the individuals of the town between the ages of 30 and 62.(2) This means that there will be a sizeable number of socially influential individuals not included in the social network; whose impact may be being mistaken for the impact of individuals at a second degree of separation.

There is enough data within the Framingham heart study to control for this effect. By only analysing those individuals who do not refer to friends outside the study's participants, we could look at a smaller but more complete set of social connections. The dependent variable would be restricted to the happiness of those individual’s who do not cite non-heart study individuals as part of their relationships. If, the same transmission of happiness at the second degree of separation occurred as with the original data then we could be more certain of the existence of network effects at this degree of separation as opposed to individuals, of one degree of separation, that were not included in the original analysis.

(1) James H Fowler and Nicholas A Christakis, Dynamic spread of happiness in a large social network: longitudinal analysis over 20 years in the Framingham Heart Study, BMJ 2008; 337: a233 (2)http://www.framinghamheartstudy.org/participants/origina l.html

Competing interests: None declared

Competing interests: None declared

Jonathan A. Mellon, student

St Anne's College, Oxford University, OX2 6HS

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19 December 2008

Lovely research. But it is a disappointment to me that the findings didn't extend to co-workers. Like many people, I spend most of my awake time working, and spend more time with colleagues than with other "friends".

Competing interests: None declared

Competing interests: None declared

Risa Denenberg, Palliative Care Nurse Practitioner


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This is an interesting paper, and I can see a lot of hard work went into it. But like many pieces of statistical research on human social experience I feel that the authors overreach themselves.

1) Firstly, the authors can not claim that people's happiness "depends" on the happiness of others. Have they sampled the whole world and every person and experience of happiness to say this? This is a generalised and normative statement no matter how statistically systematic you are that is dangerous to make about social life which I discuss further below.

2) The definition of happiness is very value laden and too simplistic which is partly to do with trying to explore human experience using quantitative measures - i.e. "asking people about the future" and "I felt that I was just as good as other people" are value laden statements about life, with these values not explored or discussed fully in the paper or with the participants.

3) The reference list is too “scientific” and I would like to have seen more reference to social context. The authors might also find Anthony Storr's book "Solitude" an interesting counter argument to their assertion that happiness “depends” on our sociability and social networks and we are “fundamentally” social beings.

4) The authors use the example of illness (acute/chronic?) as a potential source of unhappiness for patients and those around them. I'm glad that the authors use the word "potential" here, but this is where my concerns begin to mount about this kind of research and this concern features in "Bowling Alone" that social network/capital classic. If one is not careful this kind of research of trying to essentialise happiness and who experiences it and how it is obtained or passed on – these normalising tendencies - will inevitably lead to prejudice and assumptions - in this case people avoiding other people with "problems" as some people may automatically be seen as sources of social unhappiness. Indeed, much research on carers of ill people, for example, already uses the term “burden” unquestionably to describe the ill persons needs on the lives of their carer without understanding that relationship and questioning the use of this value laden term. It is only a small step from there and a few assumptions about people being happier associating with happy people, to actually create more unhappiness in ill people and not necessarily less as the authors suggest, especially if despite all the care in the world, the (chronic) illness remains. Prof Sainsbury's comment about ”not dropping your friends yet”, although humorously meant, unwittingly hits the political nail on the head and my main concern with this research genre of finding the “holy grail” of happiness.

5) The authors should have discussed some of these socio-political issues and placed their work in these arguments. Research on happiness would be better if it explored the range of things that make people “happy” as defined by the people researchers talk to, to produce conclusions that reflect diversity in the “happiness” experience and minimise conclusions that normalise. Happiness research that attempts to find generalisations about happiness will ultimately cause some people to be unhappy and marginalised and will not challenge inherent assumptions about what makes people happy, what is happiness, and who is happy in society or indeed, as Anthony Storr suggests, who is “happy alone!”

Competing interests: None declared

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Dr G Smith, Senior Research Fellow

Royal Holloway, TW20 0EX

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If happiness is as contagious as that, is it really a stretch to infer that community life is likewise contagious? Might not all this "contagious" (this viral) thinking also lead us to the more fundamental conclusion that humans are social animals not because they are social (they live in social groups) -- that would be a tautology -- but because social life is itself contagious? But in what ways would this contagion be different from Durkheimian solidarity?

Competing interests: None declared

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Mauri O. Yambo, Lecturer

Department of Sociology, University of Nairobi, 00100

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8 December 2008

There are 2 episodes in my life that would give weight to the above finding.

1. When I moved to the town I live now, I was very happy to be there but amazed that everyone who walked past seem to smile at me. It only took a short time to prove that it was their smiled respnse to my smile that was the reason.

2. In another more distant time, I was quite depressed, and found that walking up a corridor the automatic door would not open for me, although it would for anyone else walking up the same corridor ... This happened over some weeks and did little for my self-esteem. It was only later that I realised that I was walking along the edge of the corridor, and the others were walking confidently in the centre and that I was missing the beam.

Happiness (and sadness) is indeed infectious.

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Michael Tooth, GP

Sandy Bay, Tasmania, Australia

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6 December 2008

The authors- you all deserve complement for the reasons that this article once more reinforces that science and art of medicine can not be separated the art of living and attaining complete health by healthy life style ,healthy behaviour ,and healthy thoughts is again proved scientifically. Umesh chandra ojha M.D., D.T.C.D.,F.I.M.S.A.

Competing interests: None declared

Competing interests: None declared

umesh chandra, chest physician

New Delhi

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