Diffusion/Contagion Networks

Diffusion is the spread of new ideas, products, or opinions through a social system. The study of diffusions has examined various concepts such as family planning practices, medical technology, policy innovation, and educational innovations, to name just a few. Diffusion is a social process where individuals choose to take a new idea as a result of communication with another [Page 215]individual who has already adopted it. Diffusion can be seen as the “taking off” of a product, idea, or opinion through society. Thus, diffusions occurs among individuals within a social system and through the patterns of communication that exist in a social network.

This Harpers Weekly print depicts the 1884 Wall Street banking panic on the morning of May 14, spread by contagion networks.

One of the main parts of the diffusion process depends upon diffusion networks. A network is made up of people who are interconnected and linked by patterns of communication that move information along. Networks allow people to gain information about an innovation about which they are uncertain.

A number of factors can influence whether people within a network choose to adopt an innovation. One factor is whether people in a network are heterophilous (a varying degree of difference between people) or homophilous (people are similar). In many cases, homophily can be a barrier to adoption because people will not interact with dissimilar others. As network diffusion is also affected by strong and weak ties, a similar barrier arising from homophily is that when people have a strong tie, they do not exchange ideas outside their close network. In this case, weak ties are vital for information to travel among large networks. Finally, diffusion networks can reach a critical mass. When this occurs, the adoption of the innovation becomes self-sustaining. Critical mass is simply the minimum number of people needed to sustain the diffusion process.

Contagion theory is the idea that everyone who is part of a given social network will begin to engage in uniform behavior due to communication among all of the individuals in the network. The contagion theory was put forth by social psychologist Gustave Le Bon, who proposed that people in crowds often act irrationally because they submit themselves to the overpowering, contagious emotion exuded by the crowd. Regarding the link between diffusion and social networks, T. W. Valente argues that contagion is (at least partially) a function of social/network influence. Contagion is also an endogenous process, where actors are adopting and imitating the behavior of others without incentives and constraints. This behavior occurs when a situation is framed in a particular way as a substitute for information. Choices based on anticipation can be explained with the existence of networks of potential interdependencies that are not realized yet but can be expected as probable, hence leading to transient, accelerating, self-reinforcing social bubbles.

Researchers have focused on leveraging the positive benefits from social contagion, but in social networks, research has identified some of the potential risks, such as drug use among teenagers.