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Öğe Another characterization of the majority rule(Elsevier Science Sa, 2002) Asan, G; Sanver, MRGiven any (finite) society confronting two alternatives, May [Econometrica 20 (1995) 680] characterizes the majority rule in terms of anonymity, neutrality and positive responsiveness. This final condition is usually criticized to be too strong. Thus, we drop it and give a similar characterization in terms of anonymity, neutrality, Pareto optimality and a condition we call weak path independence. (C) 2002 Elsevier Science B.V. All rights reserved.Öğe Efficiency in the degree of compromise(Kluwer Academic Publ, 2004) Özkal-Sanver, I; Sanver, MRWe introduce a social choice axiom called efficiency in the degree of compromise. Our axiom is based on the trade-off between the quantity and quality of support that an alternative receives. What we mean by the quantity of support is the number of voters behind an alternative, while the quality of support is about the definition of being behind depending on the rank of an alternative in voters' preference orderings. Naturally, one can increase the quantity of support of an alternative to the expense of giving up from its quality. We say that an alternative is an efficient compromise if there exists no other alternative with at least an equal quantity of support with a higher quality. Our efficient compromise axiom is based on not choosing inefficient compromises. We introduce it and show that many standard social choice rules of the literature, such as Condorcet-consistent rules, plurality with a runoff, the Borda count and the single transferable vote, may choose inefficient compromises.Öğe Implementing matching rules by type pretension mechanisms(Elsevier Science Bv, 2005) Özkal-Sanver, I; Sanver, MRWe consider a two-sided matching model where agents' preferences are a function of the types of their potential mates. Matching rules are manipulated by type misrepresentation. We explore the implementability of the G-core in G-Strong Nash Equilibria. Although direct type pretension mechanisms rule out bad equilibria, the existence of equilibrium cannot be generally guaranteed. However, taking G as the discrete partition, the individually rational matching correspondence is partially implementable in Nash equilibria. On the other hand, incorporating a certain degree of hypocrisy in the mechanism, i.e., allowing agents to pretend different types to different potential mates, ensures the full implementability of the G-core in G-Strong Nash Equilibria. (c) 2005 Elsevier B.V. All rights reserved.Öğe Maskin monotonic aggregation rules(Elsevier Science Sa, 2006) Asan, G; Sanver, MRGiven a society confronting two alternatives, we show that the set of anonymous, neutral and Maskin monotonic aggregation rules coincides with the family of absolute qualified majority rules. We also explore the effect of incorporating Pareto optimality in our characterization. (c) 2005 Elsevier B.V. All rights reserved.Öğe Minimal monotonic extensions of scoring rules(Springer, 2005) Erdem, O; Sanver, MRNoting the existence of social choice problems over which no scoring rule is Maskin monotonic, we characterize minimal monotonic extensions of scoring rules. We show that the minimal monotonic extension of any scoring rule has a lower and upper bound, which can be expressed in terms of alternatives with scores exceeding a certain critical score. In fact, the minimal monotonic extension of a scoring rule coincides with its lower bound if and only if the scoring rule satisfies a certain weak monotonicity condition (such as the Borda and antiplurality rule). On the other hand, the minimal monotonic extension of a scoring rule approaches its upper bound as its degree of violating weak monotonicity increases, an extreme case of which is the plurality rule with a minimal monotonic extension reaching its upper bound.Öğe Nash implementing non-monotonic social choice rules by awards(Springer, 2006) Sanver, MRBy a slight generalization of the definition of implementation (called implementation by awards), Maskin monotonicity is no more needed for Nash implementation. In fact, a weaker condition, to which we refer as almost monotonicity is both necessary and sufficient for social choice correspondences to be Nash implementable by awards. Hence our framework paves the way to the Nash implementation of social choice rules which otherwise fail to be Nash implementable. In particular, the Pareto social choice rule, the majority rule and the strong core are almost monotonic (hence Nash implementable by awards) while they are not Maskin monotonic (hence fail to be Nash implementable in the standard framework).Öğe Scoring rules cannot respect majority in choice and elimination simultaneously(Elsevier Science Bv, 2002) Sanver, MRI show that there exists no scoring rule which ensures that an alternative considered as best by a strict majority is chosen while an alternative considered as worst by a strict majority remains outside of the choice set. The negative result is valid for standard scoring rules where scores depend on the number of alternatives only, as well as for generalized ones defined via vectors of scores which are functions of both the number of alternatives and agents. (C) 2002 Elsevier Science BY. All rights reserved.Öğe Sets of alternatives as Condorcet winners(Springer-Verlag, 2003) Kaymak, B; Sanver, MRWe characterize sets of alternatives which are Condorcet winners according to preferences over sets of alternatives, in terms of properties defined on preferences over alternatives. We state our results under certain preference extension axioms which, at any preference profile over alternatives, give the list of admissible preference profiles over sets of alternatives. It turns out to be that requiring from a set to be a Condorcet winner at every admissible preference profile is too demanding, even when the set of admissible preference profiles is fairly narrow. However, weakening this requirement to being a Condorcet winner at some admissible preference profile opens the door to more permissive results and we characterize these sets by using various versions of an undomination condition. Although our main results are given for a world where any two sets - whether they are of the same cardinality or not - can be compared, the case for sets of equal cardinality is also considered.Öğe Strong equilibrium outcomes of voting games are the generalized Condorcet winners(Springer, 2004) Sertel, MR; Sanver, MRWe consider voting games induced by anonymous and top-unanimous social choice functions. The class of such social choice functions is quite broad, including every t-refinement of the Plurality Rule, Plurality with a Runoff, the Majoritarian Compromise and the Single Transferable Vote, i.e., any selection from either of these social choice rules which is obtained via tie-breaking among candidates according to any total order t on the set of alternatives. As announced in our title, the strong equilibrium outcomes of the voting games determined by such social choice functions turn out to be nothing but generalized Condorcet winners, namely the (n,q)-Condorcet winners. In the case of social choice functions (such as those just listed) which are furthermore top-majoritarian, they coincide with the classical Condorcet winners.
