Networks, Crowds and Markets: Reasoning about a Highly Connected World

Over the past few decades, networks - both technical and social - have radically altered the ways in which we communicate. Access to information, resources and opinions has undergone a major change, enabling all kinds of collaborations and opportunities that previously were either restricted or unfeasible.

This excellent book by David Easley and Jon Kleinberg, both at Cornell University, is an interdisciplinary work that is well placed to channel and challenge the enthusiasm we have today for all things networked. It covers a wide range of theoretical and practical topics that effectively define the operation of networks, our relationship with them and the behaviours that they engender.

Far from being a terse, technical analysis, this is an elegant and engaging examination of the subject. Game theory, for example, suddenly gains a whole new interest when discussed, as it is here, in terms of the behaviour of buyers and sellers in an online auction - a subject that will appeal to the inner geek in those readers seeking to understand the "deep magic" of the process.

Similarly, the discussion of information networks provides some interesting insights into the philosophy and logistics of web page ranks, web search strategies and citation. The material presented may radically challenge readers' "intuitive" assumptions regarding how search engines now operate. This topic gets especially interesting when you start to develop an impression of the economic outcomes that flow from it, such as the effect that advertising can have on search behaviours - not forgetting the huge impact that a change of search engine strategy can have on a commercial organisation whose rank suddenly shifts.

It is, however, in the detailed examination of some popular network concepts that this book shows its full quality. The authors devote a whole chapter to a discussion of the "Small World" phenomenon, which describes the presence of short-chain connections between distant elements of social networks. This has entered popular thought through the concept of "six degrees of separation", a term taken from John Guare's 1990 play of that name, in which a character suggests that any two individuals on Earth are connected by a chain of no more than five intermediaries.

This comment has its roots in the classic 1967 study by social psychologist Stanley Milgram, who traced letters forwarded by mail between Nebraska and Massachusetts to determine degrees of connectivity. He found an intriguing pattern of delivery as the letters tunnelled through the social network and approached their intended targets in a series of hops of decreasing length. The median chain length between two apparently unconnected individuals was six hops. It is intriguing to look back on this hugely influential work in the knowledge that it was generated on a budget of only $680.

Today, in a digital and massively connected world, the options for study are almost endless and very significant. Easley and Kleinberg embrace recent work on blogging and email activity to show how our new and intensely active social networks operate across different levels of physical distance.

Few assumptions are made about readers' previous knowledge, although a grasp of pre-university mathematics will be helpful. The conventions used in the description and presentation of networks are explained clearly, and the authors build a well-structured and cohesive picture of network theory and practice.

The study of networks in the widest sense has a long and noble tradition, and one that has been revalorised by our new global obsession with connectivity. By placing the examples used so firmly within the immediate experience of today's networked community, the authors have given us a rich and familiar environment in which to develop our understanding.