Suchergebnisse

We characterize voting procedures according to the social choice correspondence they implement when voters cast ballots strategically, applying iteratively undominated strategies. In elections with three candidates, the Borda Rule is the unique positional scoring rule that satisfies 'unanimity' (U) (i.e., elects a candidate whenever it is unanimously preferred) and is 'majoritarian after eliminating a worst candidate' (MEW)(i.e., if there is a unanimously disliked candidate, the majority-preferred among the other two is elected). In a larger class of rules, Approval Voting is characterized by a single axiom that implies both U and MEW but is weaker than Condorcet-consistency (CON) - it is the only direct mechanism scoring rule that is 'majoritarian after eliminating a Pareto-dominated candidate' (MEPD)(i.e., if there is a Pareto-dominated candidate, the majority-preferred among the other two is elected); among all finite scoring rules that satisfy MEPD, Approval Voting is the most decisive. However, it fails a desirable monotonicity property: a candidate that is elected for some preference profile, may lose the election once she gains further in popularity. In contrast, the Borda Rule is the unique direct mechanism scoring rule that satisfies U, MEW and 'monotonicity' (MON). There exists no direct mechanism scoring rule that satisfies both MEPD and MON and no finite scoring rule satisfying CON.

In school choice problems, the widely used manipulable Immediate Acceptance mechanism (IA) disadvantages unsophisticated applicants, but may ex-ante Pareto dominate any strategy-proof alternative. In these cases, it may be preferable to aid applicants within IA, rather than to abandon it. In a laboratory experiment, we first document a substantial gap in strategy choices and outcomes between subjects of higher and lower cognitive ability under IA. We then test whether disclosing information on past applications levels the playing field. The treatment is effective in partially reducing the gap between applicants of above- and below-median cognitive ability and in curbing ability segregation across schools, but may leave the least able applicants further behind.