论文标题

先知不平等的个人公平性

Individual Fairness in Prophet Inequalities

论文作者

Arsenis, Makis, Kleinberg, Robert

论文摘要

先知的不平等是在线算法的性能保证(又称停止规则)解决以下“招聘问题”:决策者依次检查其价值观是独立随机数字的候选人,并要求最多要求候选人雇用它,然后在序列中检查未来候选人的价值。最佳停止理论的经典结果断言,存在停止规则,确保决策者将聘请一个候选人,其预期价值至少与“先知”雇用的候选人的期望值一半,即同时访问所有候选人价值的实现的人。 这种停止规则的表现良好,但可能会以多种不同的方式不公平地对待个别候选人。在这项工作中,我们确定了两种类型的个人公平性,这些公平性在最佳停止问题中可能是可取的。我们称它们为独立的公平性(IIF)和与时间无关的公平(TIF),并在招聘问题的背景下给出了精确的定义。我们提供了多项式时间算法,以查找具有离散支持的给定实例的最佳IIF/TIF停止规则,并且当需要决策者的停止规则以满足预知属性时,我们设法以$ 1/2 $的价格恢复先知不平等。在在线和离线设置中,我们还探索了最佳选择规则与缺乏个人公平约束的最佳选择规则之间的最差比率。最后,我们考虑了一个框架,在这种框架中,决策者不知道候选人值的分布,而可以从每个分布中访问独立样本。我们在离线设置中使用每个分布的一个样本提供恒定竞争力的IIF/TIF算法,在线设置中每个分布两个样本。

Prophet inequalities are performance guarantees for online algorithms (a.k.a. stopping rules) solving the following "hiring problem": a decision maker sequentially inspects candidates whose values are independent random numbers and is asked to hire at most one candidate by selecting it before inspecting the values of future candidates in the sequence. A classic result in optimal stopping theory asserts that there exist stopping rules guaranteeing that the decision maker will hire a candidate whose expected value is at least half as good as the expected value of the candidate hired by a "prophet", i.e. one who has simultaneous access to the realizations of all candidates' values. Such stopping rules have provably good performance but might treat individual candidates unfairly in a number of different ways. In this work we identify two types of individual fairness that might be desirable in optimal stopping problems. We call them identity-independent fairness (IIF) and time-independent fairness (TIF) and give precise definitions in the context of the hiring problem. We give polynomial-time algorithms for finding the optimal IIF/TIF stopping rules for a given instance with discrete support and we manage to recover a prophet inequality with factor $1/2$ when the decision maker's stopping rule is required to satisfy both fairness properties while the prophet is unconstrained. We also explore worst-case ratios between optimal selection rules in the presence vs. absence of individual fairness constraints, in both the online and offline settings. Finally, we consider a framework in which the decision maker doesn't know the distributions of candidates' values but has access to independent samples from each distribution. We provide constant-competitive IIF/TIF algorithms using one sample per distribution in the offline setting and two samples per distribution in the online setting.

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