THE 2009 LAWRENCE R. KLEIN LECTURE: DIVERSIFIED TREATMENT UNDER AMBIGUITY*

This article develops a broad theme about treatment under ambiguity through study of a particular decision criterion. The broad theme is that a planner may want to cope with ambiguity by diversification, assigning observationally identical persons to different treatments. Study of the minimax‐regret (MR) criterion substantiates the theme. The article significantly extends my earlier analysis of one‐period planning with an individualistic treatment and a linear welfare function. I show that MR treatment allocations are fractional in a large class of planning problems with nonlinear welfare functions, interacting treatments, learning, and noncooperative aspects.     

IMPACT OF OUTCOME AMBIGUITY ON SELF‐INSURANCE AND SELF‐PROTECTION: EXPERIMENTAL EVIDENCE

This experimental study examines and compares individual valuations of the two risk reduction mechanisms: self‐insurance and self‐protection in risky versus ambiguous outcome situations. Results confirm that individuals do not perceive these mechanisms differently under risk. Moreover, ambiguity in the outcome (i.e., size of loss) affects valuations weakly, and changing representations of ambiguity do not alter valuation. In general, individuals are found to be ambiguity averse for low sizes of loss and ambiguity neutral for high sizes of loss, regardless of the probability of loss. Finally, no strong support is found for any particular model of ambiguity.     

Learning Under Ambiguity

This paper considers learning when the distinction between risk and ambiguity matters. It first describes thought experiments, dynamic variants of those provided by Ellsberg, that highlight a sense in which the Bayesian learning model is extreme—it models agents who are implausibly ambitious about what they can learn in complicated environments. The paper then provides a generalization of the Bayesian model that accommodates the intuitive choices in the thought experiments. In particular, the model allows decision-makers' confidence about the environment to change—along with beliefs—as they learn. A portfolio choice application compares the effect of changes in confidence under ambiguity vs. changes in estimation risk under Bayesian learning. The former is shown to induce a trend towards more stock market participation and investment even when the latter does not.     

‘Economics with Training Wheels’: Using Blogs in Teaching and Assessing Introductory Economics

Blogs provide a dynamic interactive medium for online discussion, consistent with communal constructivist pedagogy. The author of this article describes and evaluates a blog assignment used in the teaching and assessment of a small (40–60 students) introductory economics course. Using qualitative and quantitative data collected across four semesters, students’ participation in the blog assignment is found to be associated with student ability, gender, and student perceptions of the blog. Importantly, students with past economics experience do not appear to crowd out novice economics students. Student performance is positively associated with the quality of their blog participation after controlling for student ability, suggesting that a focus on quality of student engagement could further improve learning outcomes. Students generally report overall positive experiences with the blog assignment.     

A SMOOTH AMBIGUITY MODEL OF THE COMPETITIVE FIRM

This paper examines the optimal production decision of the competitive firm under price uncertainty when the firm's preferences exhibit smooth ambiguity aversion. Ambiguity is modeled by a second‐order probability distribution that captures the firm's uncertainty about which of the subjective beliefs govern the price risk. Ambiguity preferences are modeled by the (second‐order) expectation of a concave transformation of the (first‐order) expected utility of profit conditional on each plausible subjective distribution of the price risk. Within this framework, we derive necessary and sufficient conditions under which the ambiguity‐averse firm optimally produces less in response either to the introduction of ambiguity or to greater ambiguity aversion when ambiguity prevails. In the case that the price risk is binary, we show that ambiguity and greater ambiguity aversion always adversely affect the firm's production decision.     

OPTIMISM AND PESSIMISM IN GAMES

This article considers the impact of ambiguity in strategic situations. It extends the existing literature on games with ambiguity‐averse players by allowing for optimistic responses to ambiguity. We use the CEU model of ambiguity with a class of capacities introduced by Jaffrray and Philippe (Mathematics of Operations Research 22 (1997), 165–85), which allows us to distinguish ambiguity from ambiguity‐attitude, and propose a new solution concept, equilibrium under ambiguity (EUA), for players who may be characterized by ambiguity‐preference. Applying EUA, we study comparative statics of changes in ambiguity‐attitude in games with strategic complements. This extends work in Eichberger and Kelsey (Journal of Economic Theory 106 (2002), 436–66) on the effects of increasing ambiguity if players are ambiguity averse.     

Social Learning from Private Experiences: The Dynamics of the Selection Problem

I analyse social interactions that stem from the successive endeavours of new cohorts of heterogeneous decision makers to learn from the experiences of past cohorts. A dynamic process of information accumulation and decision making occurs as the members of each cohort observe the experiences of earlier ones, and then make choices that yield experiences observable by future cohorts. Decision makers face the selection problem as they seek to learn from observation of past actions and outcomes, while not observing the counterfactual outcomes that would have occurred had other actions been chosen. Assuming that all cohorts face the same outcome distributions, I show that social learning is a process of sequential reduction in ambiguity. The specific nature of this process, and its terminal state, depend critically on how decision makers make choices under ambiguity. I use the problem of learning about innovations to illustrate.     

Ambiguity aversion among student subjects: the role of probability interval and emotional parameters

In the literature on decision-making under uncertainty, it has been shown that decision-makers tend to prefer taking gambles with known-risk probabilities (pure risk) over equivalent gambles with ambiguous probabilities. This article contributes to the ongoing discussion in the literature on cognitive and non-cognitive covariates of ambiguity aversion. Through a series of experiments, it finds that subjects are more ambiguity-averse to prospects with wide probability intervals than to an equivalent prospect with narrow intervals, and that subjects’ inherent trust, happiness and level of optimism affect the level of ambiguity aversion.     

The effect of ambiguity aversion on reward scheme choice

We test the implications of ambiguity aversion in a principal–agent problem with multiple agents. Models of ambiguity aversion suggest that, under ambiguity, comparative compensation schemes may become more attractive than independent wage contracts. We test this by presenting agents with a choice between comparative reward schemes and independent contracts, which are designed such that under uncertainty about output distributions (that is, under ambiguity), ambiguity averse agents should typically prefer comparative reward schemes, independent of their degree of risk aversion. We indeed find that the share of agents who choose the comparative scheme is higher under ambiguity.     

Ambiguity,data and preferences for information – A case-based approach

We model decision making under ambiguity based on available data. Decision makers express preferences over actions and data sets. We derive an α-max–min representation of preferences, in which beliefs combine objective characteristics of the data (number and frequency of observations) with subjective features of the decision maker (similarity of observations and perceived ambiguity). We identify the subjectively perceived ambiguity and separate it into ambiguity due to a limited number of observations and ambiguity due to data heterogeneity. The special case of no ambiguity provides a behavioral foundation for beliefs as similarity-weighted frequencies as in Billot et al. (2005) [3].     

不同生育率情形下养老保险筹资模式比较研究

理论研究普遍认为,基金制养老保险筹资模式优于现收现付制,但这几乎都是基于人均资本视角的判断。本文在外生和内生生育率两种情形下,从福利经济学视角分析基金制是否完全优于现收现付制。理论模型表明,在一定参数组合下,无论外生生育率还是内生生育率,都存在使现收现付制下社会福利高于基金制下社会福利的养老保险缴费率。模型的数值模拟显示,存在使现收现付制下社会福利更高的养老保险缴费率,且在外生生育率下（符合我国生育政策）现收现付制缴费率在12%左右社会福利最高,内生生育率下（符合发达国家生育政策）现收现付制缴费率在6%左右社会福利最高。前一数值与已有研究成果观点相近(我国社会统筹部分缴费率应下降到15%左右),后一数值与美国（62%）、日本（77%）等发达国家现收现付制养老保险缴费率相近。稳健性检验显示,只要参数赋值在合理范围内,数值模拟主要结论不变。本文为降低现行我国社会统筹部分养老保险缴费率提供了理论借鉴。     

情景喜剧《武林外传》中幽默言语的语用歧义探析

歧义被视为是一种语言的误用现象,在交际活动中,歧义不仅可以帮助语言使用者完成交际,还促进了幽默效果的产生。从语用视角出发,以话语活动中语言使用者——说话者和听话者为立足点,通过分析情景喜剧《武林外传》中幽默言语的语用歧义旨在探析语境歧义的语用功能,幽默言语产生的深层原因。     

关于全球价值链理论的研究综述

本文综述了全球价值链概念的形成过程,全球价值链的二元驱动机制,全球价值链中经济租的产生和分配,全球价值链的治理模式以及全球价值链下的产业升级。     

Experimental evidence on personality traits and preferences

Using an experiment, we test the relation between personality traits and revealed risk and ambiguity preferences, and we consider the effects of personality traits prevalence in a group on the decision making of each group member. In the experiment, subjects reveal their risk and ambiguity preferences through lottery choices. They then participate in an unstructured group chat. Afterwards, they are given the chance to revise their initial lottery choices. Results show that personality traits affect ambiguity but not risk preferences before the chat. Specifically, agreeableness is negatively related to ambiguity aversion. We also show that the probability of changing decisions after the chat is affected by the individual's personality traits but not by the traits of the other group members. The latter only affects the direction and the degree of the change.     

The Use of Narrative Interview in Teaching Principles of Macroeconomics

The author describes the design and implementation of one experiential learning assignment used in a principles of macroeconomics course. The learning exercise provides an active role for students and results in a relational experience that provides traditional undergraduate students with a frame of reference with which to interpret the impact of macroeconomic events and policy on their daily lives.     

The effect of environmental uncertainty on the tragedy of the commons

We model a common pool resource game under environmental uncertainty, where individuals in a symmetric group face the dilemma of sharing a common resource. Each player chooses a consumption level and obtains a corresponding share of that resource, but if total consumption exceeds a sustainable level then the resource deteriorates and all players are worse-off. We consider the effect of uncertainty about the sustainable resource size on the outcome of this game. Assuming a general dynamic for resource deterioration, we study the effect of increased ambiguity (i.e., uncertain probabilities pertaining to the common resourceʼs sustainable size). We show that whereas increased risk may lead to more selfish behavior (i.e., to more consumption), increased ambiguity may have the opposite effect.     

Writing in the discipline and reproducible methods: A process-oriented approach to teaching empirical undergraduate economics research

The authors of this article describe an empirical research project as a component of an upper-level undergraduate economics writing-in-the-discipline course, thus aiming to reduce the high fixed costs associated with designing an empirical research project assignment and encourage more undergraduate economics research. This project is central to the course structure and has a dual-purpose: to teach students economics writing conventions and reproducible empirical research methods. The authors present a sequenced project design and replication documentation protocol and posit that this promotes student learning and leads to improvements in organization and coherence throughout the entire research and writing process. As an essential element of the course, students learn to do econometrics through effective writing, data management, and empirical analysis.     

Costly enforcement of property rights and the Coase theorem

We examine a setting in which property rights are initially ambiguously defined. Whether the parties go to court to remove the ambiguity or bargain and settle before or after trial, they incur enforcement costs. When the parties bargain, a version of the Coase theorem holds. However, despite the additional costs of going to court, other ex-post inefficiencies, and the absence of incomplete information, going to court may ex-ante Pareto dominate settling out of court. This is especially true in dynamic settings, where obtaining a court decision today saves on future enforcement costs. When the parties do not negotiate and go to court, a simple rule for the initial ambiguous assignment of property rights maximizes net surplus. A paper circulated under the same title and dated 6 March 2000 contained the basic structure examined in this paper, but did not develop many of the results reported here. For comments, we would like to thank participants at the WZB-CEPR contests conference and seminar audiences at the University of Southern California, the University of British Columbia, UC Davis, and UC Riverside.     

A dynamic mechanism and surplus extraction under ambiguity

We study the question of auction design in an IPV setting characterized by ambiguity. We assume that the preferences of agents exhibit ambiguity aversion; in particular, they are represented by the epsilon-contamination model. We show that a simple variation of a discrete Dutch auction can extract almost all surplus. This contrasts with optimal auctions under IPV without ambiguity as well as with optimal static auctions with ambiguity—in all of these, types other than the lowest participating type obtain a positive surplus. An important point of departure is that the modified Dutch mechanism is dynamic rather than static, establishing that under ambiguity aversion—even when the setting is IPV in all other respects—a dynamic mechanism can have additional bite over its static counterparts. A further general insight is that the standard revelation principle does not automatically extend to environments not characterized by subjective expected utility.     

Recursive smooth ambiguity preferences

This paper axiomatizes an intertemporal version of the Smooth Ambiguity decision model developed in [P. Klibanoff, M. Marinacci, S. Mukerji, A smooth model of decision making under ambiguity, Econometrica 73 (6) (2005) 1849-1892]. A key feature of the model is that it achieves a separation between ambiguity, identified as a characteristic of the decision maker's subjective beliefs, and ambiguity attitude, a characteristic of the decision maker's tastes. In applications one may thus specify/vary these two characteristics independent of each other, thereby facilitating richer comparative statics and modeling flexibility than possible under other models which accommodate ambiguity sensitive preferences. Another key feature is that the preferences are dynamically consistent and have a recursive representation. Therefore techniques of dynamic programming can be applied when using this model.