UCLA physicist applies physics to best-selling books

December 01, 2004

Yes, says UCLA physicist and complex systems theorist Didier Sornette, who used statistical physics and mathematics to analyze 138 books that made Amazon.com's best-seller list between 1997 and April 2004. His team's initial results are published in Physical Review Letters Nov. 26.

"Complex systems can be understood, and the book market is a complex system," said Sornette, a professor of earth and space sciences, and a member of UCLA's Institute of Geophysics and Planetary Physics. "Each buyer is not predictable, but complex networks have a degree of predictability."

Best-selling books typically reach their sales peaks in one of two ways. The less potent way is by what Sornette calls an "exogenous shock," which is brief and abrupt. An example is "Strong Women Stay Young" by Dr. Miriam Nelson, which peaked on the list the day after a favorable review in the Sunday New York Times. A second example is Sornette's own 2002 book, "Why Stock Markets Crash: Critical Events in Complex Financial Systems," which spiked following a favorable review by Jon Markman on CNBC and TheStreet.com. "On Jan. 17, 2003, my book was ranked 2,000-something and then suddenly it was No. 17," Sornette recalled. "A few hours later, it was in the top 10. As a physicist, it looked to me like an exogenous shock to the system."

Sales are typically greater, however, when a book benefits from what Sornette calls an "endogenous shock," which progressively accelerates over time, and is illustrated in the book business by favorable word-of-mouth. Such books rise slowly, but the sales results are more enduring, and the decline in sales is slower and more much gradual, he found.

An example includes "The Divine Secrets of the Ya-Ya Sisterhood," which reached the best-seller list two years after it was published, without the benefit of a major marketing campaign. The book was popular with book clubs and inspired women to form "Ya-Ya Sisterhood" groups of their own. A second example is Nora Roberts' novel, "Heaven and Earth (Three Sisters Island Trilogy)," which peaked only after a slow rise and also fell slowly, which Sornette attributes to word of the book spreading among friends and family.

The slower peaks tend to generate more sales over time, Sornette said.

"Word-of-mouth can spread like an epidemic," he said.

The trajectories of many books' rankings are combinations of both kinds of peaks, Sornette says, which suggests that an effective, well-timed marketing campaign could combine with a strong network to enhance sales.

A specialist in the scientific prediction of catastrophes in a wide range of complex systems, Sornette said his model for analyzing peaks and falls in book sales is very similar to one he uses to understand earthquakes. He has applied techniques of physics to economic data, and has developed a quantitative model that can predict the signatures of a coming stock market crash.

"Is it possible to derive a quantitative law of how book sales behave?" Sornette asks. "We have derived a law of how a sale's shock to the system will jump up and decline over time. The books we analyzed behaved the same way. We can statistically predict how the system will evolve, how sales peaks can emerge, and we can predict the expected decline slope for books that rise sharply."

Sornette hopes this research will provide insights into complex physical systems, and will shed light on scientific questions in geophysics, biology and climatology. Sornette, who is also a research director at the University of Nice's National Center for Scientific Research in his native France, has written or co-written more than 350 papers in scholarly journals.

Complex systems in nature experience catastrophic events, such as earthquakes and climate change, but it can be difficult for scientists to tell whether these events are caused by natural, internal fluctuations or shocks from external forces. Sornette's team's success in distinguishing between internal and external causes suggests that it can be done for other extreme events in complex networks as well, he said.
-end-
Amazon.com, which updates the ranks of its top-selling books each hour, did not participate in this study.

Sornette's co-authors are Thomas Gilbert, a former UCLA graduate student who is now a graduate student at UC Berkeley's Haas Business School; undergraduate Fabrice Deschatres; and Yann Ageon at France's University of Nice.

Sornette's Web site is: http://www.ess.ucla.edu/faculty/sornette/.

University of California - Los Angeles

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