论文标题
Arrow定理中的相过渡
A Phase Transition in Arrow's Theorem
论文作者
论文摘要
Arrow的定理涉及社会选择理论中的一个基本问题:鉴于一个小组成员的个体偏好,如何汇总以形成理性的群体偏好? Arrow表明,在三个或多个候选人之间的选举中,在某些情况下,任何满足自然“公平”公理列表的投票规则都必须产生明显不合理的不及物性结果。此外,文献中Arrow定理的定量版本表明,当选民以I.I.D. \时尚的方式选择排名时,结果是不及不可忽略的。 自然要询问Arrow定理的这种定量版本是否适用于非I.I.D。\模型。为了回答这个问题,我们根据自然的非i.i.d。\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \在统计物理学中规范模型启发的选民模型下研究箭头定理;确实,Raffaelli和Marsili以前在物理学文献中引入了该模型的版本。该模型具有一个参数温度,该参数规定了不同选民之间的相关性。我们表明,在该模型中,Arrow定理的行为经历了一个惊人的相变:在模型的整个高温状态下,定量箭头定理表明,满足公理的任何投票规则的悖论的可能性是不可算力的;这很紧张,因为在接近临界温度时,悖论在成对的大多数下的概率为零,并且在其以外的选民数量中成倍小。我们证明这发生在另一个自然的相关选民模型中,并猜想这种现象是相当普遍的。
Arrow's Theorem concerns a fundamental problem in social choice theory: given the individual preferences of members of a group, how can they be aggregated to form rational group preferences? Arrow showed that in an election between three or more candidates, there are situations where any voting rule satisfying a small list of natural "fairness" axioms must produce an apparently irrational intransitive outcome. Furthermore, quantitative versions of Arrow's Theorem in the literature show that when voters choose rankings in an i.i.d.\ fashion, the outcome is intransitive with non-negligible probability. It is natural to ask if such a quantitative version of Arrow's Theorem holds for non-i.i.d.\ models. To answer this question, we study Arrow's Theorem under a natural non-i.i.d.\ model of voters inspired by canonical models in statistical physics; indeed, a version of this model was previously introduced by Raffaelli and Marsili in the physics literature. This model has a parameter, temperature, that prescribes the correlation between different voters. We show that the behavior of Arrow's Theorem in this model undergoes a striking phase transition: in the entire high temperature regime of the model, a Quantitative Arrow's Theorem holds showing that the probability of paradox for any voting rule satisfying the axioms is non-negligible; this is tight because the probability of paradox under pairwise majority goes to zero when approaching the critical temperature, and becomes exponentially small in the number of voters beyond it. We prove this occurs in another natural model of correlated voters and conjecture this phenomena is quite general.