The Bergstrom, Blume, and Varian (1986) model of voluntary contributio
ns to public goods predicts increases in public good provision as the
distribution of income becomes more unequal. This model is tested in t
he laboratory. Group behaviour conforms to the model but individual be
haviour does not. Individuals with low incomes overcontribute to the p
ublic good; individuals with high incomes undercontribute.