People contribute more to public goods, the more others give (“crowding-in”). We investigate two possible causes of crowding-in: reciprocity, the usual explanation, and conformism, a neglected alternative. The issue is important since conformism has more scope to bring about endogenous...

People contribute more to experimental public goods the more others contribute, a tendency called "crowding-in." We propose a novel experimental design to distinguish two possible causes of crowding-in: reciprocity, the usual explanation, and conformity, a neglected alternative. Subjects are...