\ Prompted vs. Unprompted Reviews 2. Selection Bias and Social Influence Bias Shape How People Write Reviews SELECTION BIAS: Shoppers who have had a negative experience The finding that anonymous reviewers typically give lower ratings is con- are more likely to make the effort of going to a sistent with our theory that “friction” causes selection bias when it comes site, creating an account, and posting a review. to reviews. When responding to an email prompt, verified buyers typically only have to make a few clicks to submit a review. Anonymous reviewers, on the other hand, must go to the review site and create an account before they can submit a review. Thus, we hypothesize that customers who are very unhappy with their purchase are much more likely to go to the effort to post an unprompted review. We also found that ratings from anonymous reviewers tend to decline over SOCIAL INFLUENCE BIAS: time while ratings from verified buyers remained steady, which suggests some degree of social influence bias is at work. Verified buyers are asked Verified buyers typically don’t see average star to fill out a review via email and are taken to a page where they don’t ratings when posting their reviews. Anonymous see any other reviews. Anonymous reviewers, on the other hand, have reviewers, on the other hand, do have this visibility to average star ratings and others’ reviews. Thus, anonymous visibility, which could influence their ratings. reviewers may be influenced by the product’s average star rating or the volume or tone of review comments. Askalidis, Y., Kim, S.J., and Malthouse E.C. (2017), “Understanding and Overcoming Biases in Customer Reviews.” Decision Support Systems. 97 (May 2017), 23-30. 15 \ How Online Reviews Influence Sales \ spiegel.medill.northwestern.edu