古树小撷

被誉为“植物王国”的云南，气候和地形复杂多样，植物资源丰富。在“王国”的重要子民—树的芸芸众生中，出类拔萃者不少。筇竹寺的“孔雀杉”，玉龙雪山的“万朵山茶”，昆明黑龙潭的“唐梅”“宋柏”，这些都是树中的明星，它们年逾数百年，芳名家喻户晓。而在这块神奇的土地上，除了这些“明星树”外，还有许多鲜为人知的古树，时时给人惊喜。走进剑川满山苍松翠柏的“蟒歇岭”，一棵奇异的树倚山而立，树干笔直。它从山脚拔地而起，高度赛过了山腰的几座庙宇而直冲山顶，那样直，那样高，那样苍翠，非常引人注目。据风景区的管理人员介…     

历史文化名城杂谈

从1982年始，国务院分三批将我国的99个城市公布为国家级历史文化名城。一个有五千多年历史的文化古国，只有不到100个历史文化名城，应该说是偏少了。然而，真正称得上名副其实的历史文化名城，那就更少了。在中国，关心历史文化名城命运的人都知道：联合国科教文组织在1996年以前，没有将一座中国城市列进世界文化遗产名录，直到1997年才看中了云南的丽江、山西的平遥。这或许对中国有点苛刻，但仔细一想，那些被列进世界文化遗产的古城，如土耳其的伊斯坦布尔历史区、叙利亚大马士革古城、耶路撒冷旧城、埃及底比斯古城等，哪个不代表着…     

Comparative cheap talk

When are comparative statements credible? We show that simple complementarity conditions ensure that an expert with private information about multiple issues can credibly rank the issues for a decision maker. By restricting the expert's ability to exaggerate, multidimensional cheap talk of this form permits communication when it would not be credible in a single dimension. The communication gains can be substantial with even a couple of dimensions, and the complete ranking is asymptotically equivalent to full revelation as the number of issues becomes large. Nevertheless, partial rankings are sometimes more credible and/or more profitable for the expert than the complete ranking. Comparative cheap talk is robust to asymmetries that are not too large. Consequently, for sufficiently many independent issues, there are always some issues sufficiently symmetric to permit comparative cheap talk.     

For those about to talk we salute you: an experimental study of credible deviations and ACDC

We test the Average Credible Deviation Criterion (ACDC), a stability measure and refinement for cheap talk equilibria introduced in De Groot Ruiz et al. (Equilibrium selection in cheap talk games: ACDC rocks when other criteria remain silent, Working paper, University of Amsterdam 2012a). ACDC has been shown to be predictive under general conditions and to organize data well in previous experiments meant to test other concepts. In a new experimental setting, we provide the first systematic test of whether and to which degree credible deviations matter for the stability of cheap talk equilibria. Our principal experimental result is that in a setting where existing concepts are silent, credible deviations matter and matter gradually, as predicted by ACDC.     

Reputational cheap talk with misunderstanding

We consider a cheap talk game with a sender who has a reputational concern for an ability to predict a state of the world correctly, and where receivers may misunderstand the message sent. When communication between the sender and each receiver is private, we identify an equilibrium in which the sender only discloses the least noisy information. Hence, what determines the amount of information revealed is not the absolute noise level of communication, but the extent to which the noise level may vary. The resulting threshold in transmission noise for which information is revealed may differ across receivers, but is unrelated to the quality of the information channel. When information transmission has to be public, a race to the bottom results: the cut-off level for noise of transmitted information now drops to the lowest cut-off level for any receiver in the audience.     

How to talk to multiple audiences

Stochastic fictitious play (SFP) assumes that agents do not try to influence the future play of their current opponents, an assumption that is justified by appeal to a setting with a large population of players who are randomly matched to play the game. However, the dynamics of SFP have only been analyzed in models where all agents in a player role have the same beliefs. We analyze the dynamics of SFP in settings where there is a population of agents who observe only outcomes in their own matches and thus have heterogeneous beliefs. We provide conditions that ensure that the system converges to a state with homogeneous beliefs, and that its asymptotic behavior is the same as with a single representative agent in each player role.     

Multidimensional cheap talk with sequential messages

This paper studies a two-dimensional cheap talk game with two senders and one receiver. The senders possess the same information and sequentially send messages about that information. In one-dimensional sequential message cheap talk games where the state space is unbounded, the information is fully transmitted under the self-serving belief, as suggested by Krishna and Morgan (2001b). However, this result depends crucially on the structure of the one-dimensional model. It generally does not hold in two-dimensional models. We consider the extended self-serving belief, which implies full information transmission even if the self-serving belief cannot work. Then, we show that the necessary and sufficient condition for the existence of the fully revealing equilibrium is that the senders have opposing-biased preferences.     

Cheap talk in games with incomplete information

The paper studies Bayesian games which are extended by adding pre-play communication. Let Γ be a Bayesian game with full support and with three or more players. The main result is that if players can send private messages to each other and make public announcements then every communication equilibrium outcome, q, that is rational (i.e., involves probabilities that are rational numbers) can be implemented in a sequential equilibrium of a cheap talk extension of Γ, provided that the following condition is satisfied: There exists a Bayesian Nash equilibrium s in Γ such that for each type t_i of each player i the expected payoff of t_i in q is larger than the expected payoff of t_i in s.     

A note on one-shot public mediated talk

Lehrer and Sorin (1997, Games Econ. Behav. 20, 131–148) use a one-shot public mediated talk model to show that, given any probability distribution on the outcomes of a finite normal-form game, there exists a public mediated talk mechanism that simulates that distribution, provided the probabilities on outcomes are rational numbers. It is shown here that a minor amendment of the very same model allows a much stronger conclusion: any distribution on the outcomes, whether the probabilities are rational numbers or not, can be obtained as the outcome of a one-shot public mediated talk mechanism.