Watts, Duncan J. 2003. Six degrees : the science of a connected age. New York: Norton.
Watts, Duncan J. 1999. Small worlds : the dynamics of networks between order and randomness. Princeton, N.J.: Princeton University Press.
Duncan Watts, I think, is a kind of rising star in recent interdisciplinary science in a connected age. Especially, in a field of management science, he and his colleagues argued viral marketing which exploits an existing social networks or communication networks (by the way, my personal view on ‘viral marketing’ sounds not positive and creates some unexpected reactions for readers who have no knowledge over epidemiology or network sciences).
Anyway, while it is a hyperbole or not, a so-called network science has lots of implications and gives scholars very valuable theoretical insights.
First, Watts’ book published in 1999 is a little bit hard for ordinary social scientists to follow the arguments and presentation of results. As he told in a book, his original idea about the topic comes from his studies on natural phenomena via theoretical lens of physics. Results are filtered via mathematical formula (in other words, lots of Greeks!!) and lots of scatterplots. However, if readers feel comfortable for the writing styles, they will find that the 1999 book is really beautifully written with great conciseness and details.
Second, the 1999 book is well structured: introduction, explanation, representation of results, interpretations, and summaries. Readers who are very familiar with the writing style of physics can skip some sentences and save their time.
However, I think ordinary social scientists (like me) will be more benefitted from the 2003 book. Basically, the 2003 book is a sort of lecture note or research diary for ordinary readers. Readers get more knowledge over the context and the academic collaboration of the author, which is also very interesting and valuable for baby-students who want to know how scientific collaboration emerges and happens and forms. (Personally, I am really enjoying over the critics of Stanley Milgram’s research about how much overblown the original paper, despite its theoretical importance)
Thus it is better for social scientific readers to start with the 2003 book and to go forward the 1999 book for understanding Watts’s arguments over small-world phenomena.