The public goods game is the classic laboratory paradigm for
studying collective action problems. Each participant chooses
how much to contribute to a common pool that returns benefits
to all participants equally. The ideal outcome occurs if everybody
contributes the maximum amount, but the self-interested strategy
is not to contribute anything. Most previous studies have found
punishment to be more effective than reward for maintaining
cooperation in public goods games. The typical design of these
studies, however, represses future consequences for today’s
actions. In an experimental setting, we compare public goods
games followed by punishment, reward, or both in the setting
of truly repeated games, in which player identities persist
from round to round. We show that reward is as effective as
punishment for maintaining public cooperation and leads to higher
total earnings. Moreover, when both options are available, reward
leads to increased contributions and payoff, whereas punishment
has no effect on contributions and leads to lower payoff. We
conclude that reward outperforms punishment in repeated public
goods games and that human cooperation in such repeated settings
is best supported by positive interactions with others.
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