Socially Nudged: A Quasi-Experimental Study of Friends’ Social Influence in Online Product Ratings

Social-networking functions are increasingly embedded in online rating systems. These functions alter the rating context in which consumer ratings are generated. In this paper, we empirically investigate online friends’ social influence in online book ratings. Our quasi-experimental research design exploits the temporal sequence of social-networking events and ratings and offers a new method for identifying social influence while accounting for the homophily effect. We find that rating similarity between friends is significantly higher after the formation of the friend relationship, indicating that with social-networking functions, online rating contributors are socially nudged when giving their ratings. Exploration of contingent factors suggests that social influence is stronger for older books and for users who have smaller networks, and that relatively more recent and extremely negative ratings cast more salient influence. The online appendix is available at https://doi.org/10.1287/isre.2017.0741 .