Fig. 1.

Experimental design study 1. Panel A: LowMPCR treatment, with endowment of 100 ECUs and MPCR of 0.4. Panel B: HighMPCR treatment with endowment of 100 ECUs and MPCR of 0.8. Panel C: HighMPCR-LowE treatment, with endowment of 50 ECUs and MPCR of 0.8. In all treatments participants face a single-decision linear public good environment in groups of four. Each member receives an endowment (E) in ECUs (Experimental Currency Units) that can be used to make continuous contributions (in increments of 1 ECU) to a Group Account. The Group Account constitutes a public good with an equal marginal return (MPCR) for all group members. The shading indicates the marginal benefit to all members of a group from a unit contribution to the public good, with stronger shading highlighting the larger collective benefit with a higher MPCR = 0.8 and the lighter shading the lower MPCR = 0.4.