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

Authors Yan Chen, Maxwell Harper, Joseph Konstan, Sherry Li

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Yan Chen
Maxwell Harper
Joseph Konstan
Sherry Li

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Yan Chen, Maxwell Harper, Joseph Konstan, and Sherry Li. Social Comparisons and Contributions to Online Communities: A Field Experiment on MovieLens. In Computational Social Systems and the Internet. Dagstuhl Seminar Proceedings, Volume 7271, pp. 1-7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2007)


We explore the use of social comparison theory as a natural mechanism to increase contributions to an online movie recommendation community by investigating the effects of social information on user behavior in an online field experiment. We find that, after receiving behavioral information about the median user's total number of movie ratings, users below the median demonstrate a 530% increase in the number of monthly movie ratings, while those above the median decrease their monthly ratings by 62%. Movements from both ends converge towards the median, indicating conformity towards a newly-established social norm in a community where such a norm had been absent. Furthermore, the social information has a more dramatic effect on those below the median, suggesting an interaction between conformity and competitive preferences. When given outcome information about the average user's net benefit score from the system, consistent with social preference theory, users with net benefit scores above average contribute 94% of the new updates in the database. In both treatments, we find a highly significant Red Queen Effect.
  • Social comparison
  • conformity
  • public goods
  • embedded online field experiment


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