The sandwich property in the voluntary contribution mechanism:The instability approach

This paper proposes an alternative explanation for the sandwich property in voluntary contribution mechanism experiments. This property refers to the phenomenon of experimental data being ``sandwiched'' between a Nash equilibrium above the midpoint of the endowment and a Nash equilibrium below this midpoint. The explanation is in terms of the instability of the system with best response dynamics, i.e., ``pulsing'' behaviors, in nonlinear environments rather than the quantal response equilibrium analysis. Since most experimental models are unstable in quasilinear environments (where the utility function is linear in a private good and nonlinear in a public good), and Cobb–Douglas environments, using equilibrium analysis is problematic.