Popularity as a Network Phenomenon

For the past two chapters, we have been studying situations in which a person's behavior or decisions depend on the choices made by other people — either because the person's rewards are dependent on what other people do or because the choices of other people convey information that is useful in the decision-making process. We've seen that these types of coupled decisions, where behavior is correlated across a population, can lead to outcomes very different from what we find in cases where individuals make independent decisions.

Here we apply this network approach to analyze the general notion of popularity. Popularity is a phenomenon characterized by extreme imbalances: while almost everyone goes through life known only to people in their immediate social circles, a few people achieve wider visibility, and a very, very few attain global name recognition. Analogous things could be said of books, movies, or almost anything that commands an audience. How can we quantify these imbalances? Why do they arise? Are they somehow intrinsic to the whole idea of popularity?

We will see that some basic models of network behavior can provide significant insight into these questions. To begin the discussion, we focus on the Web as a concrete domain in which it is possible to measure popularity very accurately. While it may be difficult to estimate the number of people worldwide who have heard of famous individuals such as Barack Obama or Bill Gates, it is easy to take a snapshot of the full Web and simply count the number of links to high-profile Web sites such as Google, Amazon, or Wikipedia.