Group rewarding can promote cooperation and save costs in public goods games

Promoting cooperation in public goods games is a long-standing problem in multiple branches of science. Reward is an effective means of promoting cooperation, but can be costly if distributed on a large scale or over long periods of time. Avoiding excessive costs is naturally of critical concern. We introduce group rewarding into public goods games and explore the impacts of such rewarding on cooperation. Cooperators are rewarded in small groups based on the number of members of cooperative groups and those members' contributions. We consider a control parameter whose adjustments lead to more cooperation while cutting costs. Simulations performed on square lattice show that group rewarding can cost-effectively lead to higher contributions to the public good. Depending on returns from the public good, which are determined by the value of the synergy factor, rewards can be kept manageable while still promoting cooperation. By running simulations on large lattices, we reveal that our approach is cost-effective even in cases of large populations.