Many consumers who are in the process of making purchasing decisions overcome the limitations of e-commerce through online reviews. Overcoming such limitations requires them to reduce the information overload presented by the overwhelming number of online reviews. Many studies have examined the factors that may influence review helpfulness. This study explores the relationship between rating extremity and review helpfulness from the perspective of normative social influence. Online reviews on Amazon.com and Yahoo! Movies are analyzed through the response surface methodology to determine whether review helpfulness increases when review ratings are consistent with the average product ratings. The findings suggest that consumers tend to consider a review helpful when its rating is close to the average rating of a product, thereby demonstrating the effect of normative social influence. We expect this study to help online marketers understand the characteristics of helpful reviews and create a strategy that decreases the information overload caused by online reviews. This study can also serve as a starting point for solving the inconclusive findings of existing studies on the relationship between review rating and review helpfulness.