Group size and collective action—Third-party monitoring in common-pool resources

This article examines the hypothesis that group size is inversely related to successful collective action. A distinctive aspect of the article is that it combines the analysis of primary data collected by the authors with a game-theoretic model. The model considers a group of people protecting a commonly owned resource from excessive exploitation. The authors view monitoring of indi-vidual actions as a collective good and focus on third-party monitoring. We argue that the costs of monitoring rise more than proportionately as group size increases. This factor along with lumpiness in the monitoring technology yields the following theoretical conclusion: Medium-sized groups are more likely than small or large groups to provide third-party monitor-ing. The authors find that the empirical evidence is consistent with this theoretical result