Beware of Early 5-Star Book Ratings on Amazon.com

A study finds that shoppers who rely on customer ratings at Amazon.com to choose books often get misled by the author's fans who reviewed the book shortly after its release.

The long-anticipated novel by a best-selling author is finally released. Pre-orders snap it up by the thousands and within hours, customer reviews appear on Amazon.com. The book is a success; the reviewers award five stars.

But after six weeks of brisk sales and heady reviews, the tone changes. The latest customer ratings at Amazon are less favourable. Instead of five stars, the bestseller now often gets a mediocre three.

The book itself hasn't changed. So what caused readers to lower their ratings?

This ratings pattern was discovered by researchers studying trends in book reviews on Amazon. Reviews declined for 70 percent of the 2200 hardcover books that they tracked from the release date.

Researchers found this effect even though they discarded the first five reviews posted for each book. Doing so helped them avoid including reviews written by possible forum manipulators, positive reviews from, for instance, the author's friends or colleagues. That left the study with data from 135,000 customer reviews.

Why Ratings Decline

Productive authors are most likely to receive declining reviews. The honest bias in early reviews arises because devotees who follow an author become the first to buy that author's latest book. Fans are already predisposed to liking the author's work. The declines in ratings reflect different tastes between early readers and later purchasers, who aren't such avid fans.

About one-quarter of declining reviews show a sharp ratings dip that typically hits bottom from six weeks through to 19 weeks after the book's release. After that, ratings rise slightly, then settle at a steady long-term average.

This overshoot in the ratings dip occurs because the stellar early ratings attract more mainstream readers, who end up disappointed. A positive review bias can increase book sales substantially.

Early Reviews Mislead Buyers

For a broader audience, the highly-rated new release doesn't live up to the initial exuberant reviews. Biased reviews mislead subsequent shoppers into buying a book they might not otherwise get. Some vent their disappointment in an online review that pulls down the book's rating.

The pattern discovered by this study demonstrates that shoppers who rely on customer ratings to choose books, don't account for the inherent bias of early reviewers. Those shoppers are misled by the author's fans who reviewed the book shortly after its release.