Choosing the level of a public good when agents have an outside option

The work examines strategy-proof social choice functions which select a level or the location of a public good when its consumption is not compulsory. We assume that agents have single-peaked preferences on the consumption of the public good as well as a reservation utility. Agents opt out of the good whenever they get a utility smaller than their reservation utility. We characterize strategy-proof and efficient social choice functions as well as the ones which are anonymous and group strategy-proof. Finally, we observe that for given preferences a Condorcet winner may not exist. Copyright Springer-Verlag 2004