5.61 Testimonials and Harry Potter: Amazon and other online bookstores offer readers the opportunity to write their own book reviews, and many potential readers scour these reviews to decide which books to buy. Harry Potter books attract a great deal of these reader reviews. One Amazon reviewer, “bel 78, ” submitted her review of Harry Potter and the Half-Blood Prince from Argentina. Of the book, she said, “It’s simply outstandingly good, ” and suggested that readers of her review “run to get your copy.” Do these reviews have an impact? In this case, more than 900 people had read bel 78’s review, and close to 700 indicated that the review was helpful to them.

a. Imagine that you’re deciding whether to buy Harry Potter and the Half-Blood Prince, and you want to know what people who had already read the book thought before you invest the money and time. What is the population whose opinion you’re interested in?

b. If you read only bel 78’s review, what is the sample from which you’re gathering your data? What are some of the problems in relying on just this one review?

c. About 5500 readers had reviewed this book on Amazon by 2016. What if all reviewers agreed that this book was amazing? What is the problem with this sample?

d. Given no practical or financial limitations, what would be the best way to gather a sample of Amazon users who had read this Harry Potter book?

e. A friend plans to order a book online to take on spring break. She is reading online reviews of several books to make her decision. Explain to her in just a few sentences why her reliance on testimonials is not likely to provide her with objective information.