Fair comment

Illustration by Pelle Mellor

IF A book on Amazon.com, the leading online retailer, already has hundreds of reviews, is it worth bothering to add another? Evidently some people think it is. Peter Hoflich, a financial journalist based in Singapore, recently wrote the 3,250th review of “Harry Potter and the Deathly Hallows”, for example. “I wonder if anyone will benefit from my review, especially since there are so many,” he muses. Oddly enough, somebody might. That is because the raw number of reviews or comments, and the proportion of positive and negative ones, send useful signals to other people, even if they do not trawl through all of them. Accordingly, websites make it as easy as possible for people to add their comments.

Amazon was a pioneer in this regard: it has allowed customers to post reviews of books and other products for many years. Initially, publishers and authors were worried that allowing negative reviews would hurt sales. Online retailers have generally been reluctant to allow users to leave comments, says John McAteer, Google's retail industry director, who runs shopping.google.com, the internet giant's comparison-shopping site. But a handful of bad reviews, it seems, are worth having. “No one trusts all positive reviews,” he says. So a small proportion of negative comments—“just enough to acknowledge that the product couldn't be perfect”—can actually make an item more attractive to prospective buyers.

The sheer volume of reviews makes far more difference, according to Google's analysis of clicks and sales referrals. “Single digits didn't seem to move the needle at all,” says Mr McAteer. “It wasn't enough to get people comfortable with making that purchase decision.” But after about 20 reviews of a product are posted, “We start to see more reviews—it starts to accelerate,” says Sam Decker, the chief marketing officer of Bazaarvoice, a firm that powers review systems for online retailers.

His company's research shows that visitors are more reluctant to buy until a product attracts a reasonable number of reviews and picks up momentum. In a test with Kingston, a maker of computer memory, Bazaarvoice collected reviews of Kingston products from the firm's website and syndicated them to the website of Office Depot, a retailer. As a result there were more than ten reviews per product, compared with one or two for competitors' offerings. The result was a “drastically” higher conversion rate, which extended even to other Kingston products that lacked the additional reviews.

Yet even when a product has attracted hundreds or even thousands of reviews, they keep coming in. Five reviews of the first book in the popular “Twilight” series, which was published in October 2005, were posted on Amazon.com on a typical day recently. Most retailers and comparison sites try to strike a balance between recent reviews and helpful ones. Allowing visitors to rate reviews allows the most informative to rise to the top. And displaying recent reviews indicates that people are still interested in the product.

“Most people only look at the most recent—they don't go back and look at the first review,” says Mr McAteer. Clay Shirky, a consultant on social media, points out that reverse-chronological sorting, which is how blog posts, comments and reviews are generally displayed on the web, “gives people a latent expectation that recency matters.” People like to read recent reviews, but why does anyone post new ones? Mr Shirky suggests that in many cases, writing a review is more like writing fan mail (or hate mail) for a product, and the people who post them do not really expect it to be read.

But Daphne Durham, books editor at Amazon, says some reviewers really do want to shape others' opinions. “Someone out there is reading Harry Potter for the first time,” she says. This prompts other readers who feel strongly about it “to debunk the hype, or to validate it.” On Amazon, indeed, the most prolific reviewers are promoted almost as celebrities in their own right. This prompts reviewers to focus on quantity, not quality, however, so Amazon recently changed its ranking system. Now the “helpfulness” of reviews is taken into account, causing Harriet Klausner, the most prolific reviewer with over 18,000 reviews to her credit, to drop below 500th place in the rankings. Readers rated her reviews as helpful 71% of the time, compared with 95% for the new number-one reviewer, “Mark”, who has written fewer than 500 reviews.

What is true for reviews does not appear to apply to comments left on news stories or blogs, however. “You can probably have a decent discussion until you get to about 350 comments,” says Markos Moulitsas, the founder of Daily Kos, a popular left-leaning political site. But after that, he says, “most outside people will stay away from the thread, and further growth will come from people already inside that thread carrying forth a discussion, debate, or argument.” Such discussion threads are more of a conversation, and the page they inhabit usually has a limited lifespan during which people continue to post—unlike the Amazon pages for the “Harry Potter” books, which continue to attract reviews even today, years after the books' publication.