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How Behavior Spreads

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How Behavior Spreads

The Science of Complex Contagions

Princeton UP,

15 min read
7 take-aways
Audio & text

What's inside?

How social and organizational networks accelerate or stop the spread of important ideas and better behaviors.

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  • Scientific
  • Applicable
  • Concrete Examples


University of Pennsylvania professor Damon Centola argues that the more complex an idea, technology or new behavior, the less likely large networks of weak ties will promote its adoption. In an increasingly connected world of loose and long ties, this matters. Through reference to extensive experimentation and research, Centola shows that the spread and adoption of important ideas – like getting vaccinated, voting or adopting healthier behaviors – require tight networks of strong ties.


Social contagions include ideas and behaviors.

The spread, or diffusion, of social contagions occurs through social networks. Conventional wisdom about how this occurs proves fundamentally wrong.

Consider how 1960s Korea dealt with runaway population growth. The Korean government sought to slow it through social influence via peer networks. Koreans in villages and towns gently diffused information about contraception to neighbors and close friends. These clusters of close ties overlapped, so that gradually, everyone in a village would get the message from a trusted peer.

Most theorists and students of social networking assume that ideas spread through society quickly and efficiently along weak ties – people who loosely associate with each other. This works well for simple ideas and information – and for highly transmissible diseases – but not when involving a potential contagion of complex ideas, a new technology adoption or a substantive behavior change. 

Weak ties in networks may slow the spread of innovation and behavior change.

Dangerous and detrimental contagions often spread despite efforts to contain...

About the Author

Sociology professor Damon Centola directs the Network Dynamics Group at the University of Pennsylvania.

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