This research was conducted by Judith A. Chevalier and Dina Mayzlin at Yale University, USA


This paper looked into the effect of online customer reviews on the sales of books at Amazon and Barnes & Noble. They found that most of the reviews on both sites tended to be positive, that positive reviews were associated with a subsequent increase in sales, and negative reviews impacted more strongly to suppress sales than positive reviews enhanced them. They also found that people tend to read the reviews rather than simply looking at the star ratings given by online reviewers.

The fate of bestsellers at Amazon and Barnes & Noble

They tracked the sales of a large sample of books drawn from Global Books In Print and Publishers Weekly bestseller lists (in the end they had data for over 6,000 book titles published between 1991 and 2002). After whittling down the sample by removing duplicates and books that sold so little they were unlikely to attract a review at either site they were left with 2387 titles. They collected data from Amazon and on the price, delivery time and reviews of each title. They also looked at sales ranking (rather than strictly number of sales). They did this at three times: May 2003, August 2003 and May 2004.

An increase in relative, if not absolute, sales

By conducting analysis that controlled for all the various bits of data they collected they found that positive reviews did indeed increase sales at both Amazon and Barnes & Noble. However, they are cautious to point out that the effect is on relative sales (ie how popular a book is relative to other books). They have no evidence to support the fact that the total number of all books sold would increase if there were more positive reviews for all books published.

Title The effect of word of mouth on sales: online book reviews
Author(s) Chevalier, J. A. & Mayzlin, D.
Publication date 2006
Source Journal of Marketing Research, Vol 43, Iss 3, pp 345-354
Open Access Link
Author email