The Diffusion of Innovation, 5th ed by Everett Rogers

Interpersonal networks influence people to adopt innovations. Opinion leadership is the degree to which a individual in able informally to influence other individuals’ attitudes or overt behavior in a desired way with relative frequency. The impact of opinion leaders helps explain why the diffusion curve is S-shaped.

This model postulates that the mass media has direct, immediate, and power effects on a mass audience. They were perceived as a strong influence on behavior change during the 40’s and 50’s. Later research show that it was too simple, too mechanistic, and too gross to give an accurate account of media effects. It ignored the role of opinion leaders.

This model holds that information flows from the mass media to opinion leaders who then influence people via face-to-face contact. Mass communication channels are primarily knowledge creators, whereas interpersonal networks are more important in persuading individuals to adopt or reject.

Homophily is the degree to which a pair of individuals who communicate are similar. Such similarity may be attributes such as beliefs, education, differences in technical competence, and socioeconomic status. It is the opposite of heterophily. Homophily occurs frequently in communication and is more effective. It requires less effort and enjoys a greater comfort level.

Heterophilous communication has a special informational potential even though it may occur rarely. Heterophilous network links often connect two cliques, thus spanning two sets of socially dissimilar individuals. Such “bridges” are especially important in conveying information about innovations. Homophily accelerates diffusion but limits the spread. People willing to engage in heterophyllous communication are less concerned about things like education and social status and are more innovative.

Sociometric – Ask system members who they go to for advice. Take me to your leader. Requires lots of interviews and analysis.
Informant’s ratings – If you can identify people in the system who know it well, ask them.
Self-designating method – Ask people if they think they are opinion leaders.
Observation – Works best in small systems when people don’t know they are being observed.

Polymorphism is the degree to which an individual acts as an opinion leader for a variety of topics. The opposite, monomorphism, is the degree to which a person acts as the opinion leader for a single topic. When looking at opinion leadership you need to be aware of how diverse the topic are that you are interested in.

On the night of April 18-19, 1775, two riders rode out from Boston to warn the local populace that British troops were marching from Boston to capture colonial leaders, John Hancock and Samuel Adams, and to capture stores of guns and ammunition. Paul Revere was much more effective because he knew who the anti-British opinion leaders were. He also persuaded young men on horseback returning from courting missions to spread the alarm. Dawes simply knocked on random doors causing most of the occupants to simply go back to sleep.

Opinion leaders have greater exposure to mass media. This puts them in greater contact with change agents. They are more cosmopolite and bring ideas across boundaries between groups.
They have extensive interpersonal network links. They are socially accessible.
They have higher socioeconomic status than their followers and they are recognized as trustworthy and competent experts about innovations.

The information exchange potential or communication networks is negatively related to their degree of proximity and homophily. Heterophilous links of low proximity are the weak ties that are rare yet play a crucial role in the flow of information about an innovation. An individual’s intimate friends rarely possess much information that the individual doesn’t already know.

One individual learns from another by means of observational modeling. One observes another’s behavior and then does something similar. The modeled behavior is similar but not an exact copy. Nonverbal communication is important in behavior change. This can happen via a social network, a public display, or by viewing visual media.

When critical mass is reached diffusion becomes self-sustaining. This is the point where the adoption rate accelerates. While the concept started with nuclear physics, it shows up in many fields including epidemiology, fashion, survival of species, language systems, racial integration, and political movements. This is why some innovations become more valuable as more people adopt them. The telephone and the Internet are examples.