Individual versus group strategy-proofness: when do they coincide?
|Speaker:||Professor Salvador Barbera, Universitat Autonoma de Barcelona|
|Date:||Friday 5 March 2010|
|Location:||MBA Lecture Theatre|
A social choice function is group strategy-proof on a domain if no group of agents can manipulate its final outcome to their own benefit by declaring false preferences on that domain. Group strategy-proofness is a very attractive requirement of incentive compatibility. But in many cases it is hard or impossible to find nontrivial social choice functions satisfying even the weakest condition of individual strategy-proofness. However, there are a number of economically significant domains where interesting rules satisfying individual strategy-proofness can be defined, and for some of them, all these rules turn out to also satisfy the stronger requirement of group strategy- proofness. This is the case, for example, when preferences are single-peaked or single-dipped, or for some subsets of separable preferences. In other cases, this equivalence does not hold. We provide sufficient conditions defining domains of preferences guaranteeing that individual and group strategy-proofness are equivalent for all rules defined on these domains. We provide a partial answer regarding the necessity of our conditions.