Social Comparisons and Contributions to Online Communities: A Field Experiment on MovieLens

  • Yan Chen B
  • Maxwell Harper F
  • Konstan J
 et al. 
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We design a field experiment to explore the use of social comparison to increase contributions to an online community. We find that, after receiving behavioral information about the median user's total number of movie ratings, users below the median demonstrate a 530-percent increase in the number of monthly movie ratings, while those above the median decrease their ratings by 62-percent. When given outcome information about the average user's net benefit score, above-average users mainly engage in activities that help others. Our findings suggest that effective personalized social information can increase the level of public goods provision. (JEL C93, H41) With the increasing popularity of the Internet, information technology is changing the way we interact, entertain, communicate and consume. In online communities, groups of people meet to share information, discuss mutual interests, play games and carry out business. Users of communities such as SourceForge ( and Wikipedia contribute information goods, which are typically shared as public goods. However, despite the popularity of online communities, many such communities fail due to nonparticipation and under-contribution. For example, Brian Butler (2001) found that 50-percent of social, hobby, and work mailing lists had no traffic over a 122 day period. Under-contribution is a problem even in active and successful online communities. For example, in MovieLens (, an online movie recommendation website that invites users to rate movies and, in return, makes personalized recommendations and predictions for movies the user has not already rated, under-contribution is common. More than 22-percent of the movies listed on the site have fewer than 40 ratings, so few that the software cannot make accurate predictions about which users would like these movies (Dan Cosley, Pamela Ludford and Loren Terveen 2003). Similarly, Eureka, a Xerox Corporation online information sharing system, which enables its 20,000 worldwide customer service engineers to share repair tips, also suffers from under-contribution. While many service engineers download machine repair tips from Eureka, only an estimated 20-percent have submitted a validated tip to

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  • By Yan Chen

  • F Maxwell Harper

  • Joseph Konstan

  • Sherry Xin Li

  • Rachel Croson

  • John Duffy

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