The physics of best-sellers

UCLA physicist and complex systems theorist Didier Sornette 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 the "Physical Review Letters," Nov. 26.

"Complex systems can be understood, and the book market is a complex system," says Sornette. "Each buyer is not predictable, but complex networks have a degree of predictability."

A specialist in the scientific prediction of catastrophes in a wide range of complex systems, Sornette says his model for analyzing peaks and falls in book sales is similar to one he uses to understand...earthquakes.

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 illustrative example of this would be "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."

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. An example would be "The Divine Secrets of the Ya-Ya Sisterhood," which reached the best-seller list only 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 would be 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 says. "Word-of-mouth can spread like an epidemic."

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.

Sort of like a series of mini-earthquakes. Didn't know bookselling could get that exciting -- perhaps we should all look into that...

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Read more offbeat science stories in the DEC/JAN issue of "Arte Six."