How strategy sensitive are contributions?

We test six hypotheses for contributions in dilemma games, a category that includes the prisoner's dilemma and public goods games. Our experiment focuses specifically on the strategic interdependence of contributing behavior, and manipulates the strategy space of a two-person dilemma game especially designed for the task. The hypothesis that contributors have non-linear preferences over own and the other player's payoffs accurately matches the strategic pattern of contributing that we observe across treatments. None of the reasons for contributing advanced by the other hypotheses, whether alone or in additive combination, does so.