Cooperation, but no reciprocity: Individual strategies in the repeated Prisoner's Dilemma
Cooperation, but no reciprocity: Individual strategies in the repeated Prisoner's Dilemma
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DOI：
10.1257/aer.20130675
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发表时间：
2015-08
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影响因子：
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通讯作者：
Yves Breitmoser
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作者：
Yves Breitmoser
我们对反复PD的理解的最新进展是检测实验室受试者开始预测性合作的阈值d*。这个阈值大大高于经典阈值“存在严峻均衡”，并已由Blonski，Ockenfels和Spagnolo（2011，BOS）公理化表征。在本文中，我推导出它的行为基础。首先，证明了阈值等价于存在一个“Semi-Grim”均衡s_cc>s_cd=s_dc>s_dd。它是合作的（s_cc>0.5），非互惠的（s_cd=s_dc），并对不完美的监控（“无信念”）具有鲁棒性。接下来，我表明，非互易条件s_cd=s_dc也遵循从鲁棒性随机效用扰动（logit均衡）。最后，我重新分析了最近四个实验中的策略，发现大多数受试者确实在均衡策略时使用了Semi-Grim，这解释了d* 的预测成功。
A recent advance in our understanding of repeated PDs is the detection of a threshold d* at which laboratory subjects start to cooperate predictively. This threshold is substantially above the classic threshold "existence of Grim equilibrium" and has been characterized axiomatically by Blonski, Ockenfels, and Spagnolo (2011, BOS). In this paper, I derive its behavioral foundations. First, I show that the threshold is equivalent to existence of a "Semi-Grim" equilibrium s_cc>s_cd=s_dc>s_dd. It is cooperative (s_cc>0.5), non-reciprocal (s_cd=s_dc), and robust to imperfect monitoring ("belief-free"). Next, I show that the no-reciprocity condition s_cd=s_dc also follows from robustness to random-utility perturbations (logit equilibrium). Finally, I re-analyze strategies in four recent experiments and find that the majority of subjects indeed plays Semi-Grim when it is an equilibrium strategy, which explains d*'s predictive success.