Authors: Nicholas Christakis and James Fowler



This book explores social networks, real and virtual. Describing them as ‘…intricate things of beauty…’ (page ix), the authors show the extensive influence social networks have on individuals and societies. The concepts they discuss go far beyond the commonplace expectations of networks. How, for instance, does your friend’s friend’s friend’s weight influence your weight? How does one sick person affect the health of other family members? More disturbingly, how does your social network restrict your autonomy? The authors address these and other curious and practical properties of social networks. Throughout the book, the authors stress the overarching significance of networks, saying ‘the key to understanding people is understanding the ties between them’ (page x).



The authors started by explaining the structure of networks. They describe the ‘nodes‘ that make them up, and their connecting links which they depict as ‘…chains that branch like lightning bolts forming intricate patterns throughout human society’ (pages x). They defined different characteristics of networks such as connectedness and contagion (page 16), and remarked on their emergent properties (page 26). They show the power of social networks which influence significant life choices such as the selection of marriage partners.

A major part of the book examined the spread of different phenomena within networks. The authors discuss this ‘hyperdyadic spread‘ with illustrative anecdotes such as the Corsican family ravaged by a cascade of revenge killings (page 3). They show how behavioural imitation may result in the spread of harmful practices (page 112). Such ‘negative spread’ may lead to the adoption of unhealthy sexual and dietary habits, and physical symptoms such as headaches, back pain, anxiety and depression (page 31). They give several examples of ‘diffusion’ within networks of such curious phenomena as suicide cascades, laughing epidemics, and mass psychological illnesses. The book explores the biological and neuroscientific explanations for these with reference to the brain’s mirror neurone system (page 39).




The book however stresses that the influence of networks is not limitless. The spread of trends within networks is typically restricted to a ‘three degree of influence rule‘; this constrains how trends such as ideas, innovation, political views, and habits spread within a network (page 28). Whilst the strong links within networks are important, the authors emphasise that the wider effects of networks require the weak links which connect individual networks. Making reference to the seminal work of Mark Granovetter, the authors state that ‘strong ties may bind individuals together into groups, but weak ties bind groups together into the larger society…'(page 157). The authors also address digital social networks with reference to websites such as Google, Facebook, YouTube, Wikipedia, eBay and World of Warcraft. They reviewed the similarities of virtual and real social networks, and showed how the two types of network often interact and sometimes merge.

Drawing together their experience, the authors made several recommendations on how the knowledge of social networks could aid health policy development. They suggest, for example, that habit-reforming health campaigns should target groups rather than individuals (page 130). Referring to work done by Brian Uzzi which shows a correlation between size of research groups and the impact of their research output, the authors recommend large collaborative research over more confined team efforts (page 164).” target=”_blank”>

One of the authors, Physician Nicholas Christakis, giving a TED talk on ‘Connected’


The book successfully demonstrates the importance of social networks. It is an exciting excursion into a topic that feels familiar, but which has very surprising revelations. The authors have comprehensively researched the topic, and traversed a staggering diversity of disciplines. With flawless writing devoid of technical language, the book shows how networks influence health and life outcomes. I particularly enjoyed the anecdotes sprinkled throughout the book; these graphically show how our ever-widening, real-life and digital social networks influence us individually and collectively.


Networks are crucial for healthcare and this book shows the extent of their influence. The increasing role of networks requires doctors to appreciate their benefits and risks. Most of the books contents are relevant to healthcare, not least because one of the authors (NC) is a physician. I therefore unstintingly recommend it all doctors.



  • Publisher, place, date: Harper Press, London, 2009
  • Edition: 1st
  • Number of chapters: 9
  • Pages: 338
  • ISBN: 978-0-00-730360-1
  • Price: £7.99
  • Star rating: 5 stars


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