Non-Cooperative Behavior in a Public Goods Experiment with Interior Solution

We designed an experiment on voluntary contribution to a public good with interior solution. The treatment variable is the equilibrium level of contribution. We observe that the verage overcontribution rate (cooperation) is affected by the equilibrium level of contribution. Overcontribution is statistically significant only at the lower level of equilibrium contribution but not at the higher levels. We discuss several possible explanations, and suggest that behavioral heterogeneity might account for the observed pattern of overcontribution. Simulation results based on a simple model of heterogeneous interacting agents confirm our intuition.