Glossary
Social diffusion
What is social diffusion?
Social diffusion is the spread of innovations, behaviors, information, or practices through social networks. It concerns both what spreads and the connections through which it travels.
How networks matter
Some forms of spread can occur after one contact. Others may require reinforcement from several people. These are often described as simple and complex contagions. A network that reaches many distant people may behave differently from one with tightly connected clusters.
Research example
In Centola’s 2010 experiment, participants joined an online health community and were assigned “health buddies.” The behavior being tracked was registration for a separate online health forum. When someone registered, their buddies received notifications inviting them to join.
Participants were randomly assigned to clustered or rewired random networks. The number of buddies per person was held constant across the corresponding conditions; what changed was how those connections overlapped. Registration spread farther and faster in the clustered networks.
The design distinguishes reach from reinforcement. A connection into a distant cluster can carry a message to someone new, but several overlapping contacts can expose a person to adoption by multiple buddies. The latter pattern supported this forum-registration behavior. The experiment did not show that every health behavior requires multiple exposures or that a fixed number of friends makes someone exercise.
Why it matters
When trying to spread a practice, consider the contacts and reinforcement it may require. A pattern found in an online experiment is a starting point for testing a real program.