We consider mechanisms for truthfully eliciting probabilistic predictions from a group of experts. The standard approach -- using a proper scoring rule to separately reward each expert -- is not robust to collusion: experts may collude to misreport their beliefs in a way that guarantees them a larger total reward no matter the eventual outcome. Chun and Shachter (2011) termed any such collusion "arbitrage" and asked whether there is any truthful elicitation mechanism that makes arbitrage impossible. We resolve this question positively, exhibiting a class of strictly proper arbitrage-free contract functions. These contract functions have two parts: one ensures that the total reward of a coalition of experts depends only on the average of their reports; the other ensures that changing this average report hurts the experts under at least one outcome.

翻译：我们考虑建立机制,从一个专家组实实在在地获得概率预测。标准方法 -- -- 使用适当的评分规则来分别奖励每位专家 -- -- 并不是有力的串通舞弊:专家们可能串通舞弊,以保障他们获得更大的全部报酬,无论最终结果如何。 Chun 和Shachter (2011年)称任何此类串通为“套利 ”, 并询问是否有任何真实的招揽机制使套利变得不可能。我们积极解决这一问题,展示了严格适当的无套利合同功能。 这些合同功能有两个部分:一是确保专家联盟的总报酬仅取决于其报告的平均值;二是确保改变这一平均报告至少伤害到一个结果的专家。