How Do One's Peers on a Leaderboard Affect Oneself?

Leaderboards are a workhorse of the gamification literature. While the effect of a leaderboard has been well studied, there is much less evidence how one's peer group affects the treatment effect of a leaderboard. Through a pre-registered field experiment involving more than 1000 users on an online movie recommender website, we expose users to leaderboards, but different sets of users are exposed to different peer groups. Contrary to what a standard behavioral model would predict, we find that a user's contribution increases when their peer's scores are more dispersed. We also find that decreasing average peer contributions motivates a user to contribute more. Moreover, these effects are themselves mediated by group size. This sheds new light on existing theories of motivation and demotivation with regards to leaderboards, and also illustrates the potential of using personalized leaderboards to increase contributions.