Going Beyond Suffering in Public Goods Games When Low Contributions Are Inefficient: Experimenting with Two Institutions

We analyze a public goods game with linearly increasing marginal returns to contributions, leading to a non-monotonic group payoff. By allowing the incentive to freeride to persist at all contribution levels, we preserve the usual social dilemma of voluntary public goods provision. We compare two conditions in which both let participants face the voluntary contribution task over a finite number of rounds: one implements it as a static game (Baseline condition), and the other implements it as a dynamic game with four successive stages of simultaneous contribution choices within each round (Milestone condition). Our data show that cooperation in the Baseline condition is rare and mostly limited to the first few rounds. The evidence for the Milestone condition is much more encouraging: contributions beyond suffering are substantial and fairly stable across rounds, although full contributions remain rare. This evidence suggests that the Milestone protocol is a promising institutional device for enhancing voluntary cooperation.