Professors Ghose, Smith and Telang chose a random sample of books in print and studied how often used copies were available on Amazon. In their sample, they found, on average, more than 22 competitive offers to sell used books, with a striking 241 competitive offers for used best sellers. The prices of the secondhand books were substantially cheaper than the new, but of course the quality of the used books (in terms of wear and tear) varied considerably.
According to the researchers’ calculations, Amazon earns, on average, $5.29 for a new book and about $2.94 on a used book. If each used sale displaced one new sale, this would be a less profitable proposition for Amazon.
But Mr. Bezos is not foolish. Used books, the economists found, are not strong substitutes for new books. An increase of 10 percent in new book prices would raise used sales by less than 1 percent. In economics jargon, the cross-price elasticity of demand is small.
One plausible explanation of this finding is that there are two distinct types of buyers: some purchase only new books, while others are quite happy to buy used books. As a result, the used market does not have a big impact in terms of lost sales in the new market.
Moreover, the presence of lower-priced books on the Amazon Web site, Mr. Bezos has noted, may lead customers to "visit our site more frequently, which in turn leads to higher sales of new books." The data appear to support Mr. Bezos on this point.
Applying the authors’ estimate of the displaced sales effect to Amazon’s sales, it appears that only about 16 percent of the used book sales directly cannibalized new book sales, suggesting that Amazon’s used-book market added $63.2 million to its profits.
Furthermore, consumers greatly benefit from this market: the study’s authors estimate that consumers gain about $67.6 million. Adding in Amazon’s profits and subtracting out the $45.3 million of losses to authors and publishers leaves a net gain of $85.5 million.