Coming and going: Experiments on endogenous group sizes for excludable public goods

When a public good is congestible, individuals wanting to provide the public good face challenges in forming groups of optimal size, selecting the members of the group, and encouraging members to contribute for the public good. We conduct a series of experiments in which subjects form groups using three different entry and exit rules. The experimental results are analyzed in terms of group size, the level of public good provision, social efficiency, congestion and group stability. We find that entry restriction improves the average earnings for some individuals compared to free entry/exit or restricted exit. For a given group size, individuals under the restricted entry rule contribute more for the provision of the collective good. Also, for a given average contribution level of group members, subjects under the restricted entry rule suffer less from the congestion problem and are better able to form groups of sizes closer to the optimal.