VOTING AND LOTTERY DRAFTS AS EFFICIENT PUBLIC-GOODS MECHANISMS

This paper characterizes interim efficient mechanisms for public good production and cost allocation in a two-type environment with risk-neutral, quasi-linear preferences and fixed-size projects, where the distribution of the private good, as well as the public goods decision, affects social welfare. An efficient public good decision can always be accomplished by a majority voting scheme, where the number of ''YES'' votes required depends on the welfare weights in a simple way. The results are shown to have a natural geometry and an intuitive interpretation. We also extend these results to allow for restrictions on feasible transfer rules, ranging from the traditional unlimited transfers to the extreme case of no transfers. For a range of welfare weights, an optimal scheme is a two-stage procedure which combines a voting stage with a second stage where an even-chance lottery is used to determine who pays. We call this the ''lottery draft mechanism''. Since such a cost-sharing scheme does not require transfers, it follows that in many cases transfers are not necessary to achieve the optimal allocation. For other ranges of welfare weights the second stage is more complicated, but the voting stage remains the same. If transfers are completely infeasible, randomized voting rules may be optimal. The paper also provides a geometric characterization of the effects of voluntary participation constraints.