Rational Expectations and Ambiguity: A Comment on Abel

Abel (2002) proposes a resolution of the riskfree rate and the equity premium puzzles by considering pessimism and doubt. Pessimism is characterized by subjective probabilistic beliefs about asset returns that are stochastically dominated by the objective distribution of these returns. The subjective distribution is characterized by doubt if it is a mean- preserving spread of the objective distribution. This note offers a decision theoretic foundation of Abel's ad-hoc definitions of pessimism and doubt under the assumption that individuals exhibit ambiguity attitudes in the sense of Schmeidler (1989). In particular, we show that the behavior of a representative agent, who resolves her uncertainty with respect to the true distribution of asset returns in a pessimistic way, is the equivalent to pessimism in Abel's sense. Furthermore, a representative agent, who takes into account pessimistic as well as optimistic considerations, may result in the equivalent to doubt in Abel's sense.

Rational Expectations and Ambiguity: A Comment on Abel (2002)

Abel (2002) proposes a resolution of the riskfree rate and the equity premium puzzles} by considering pessimism and doubt. Pessimism is characterized by subjective probabilistic beliefs about asset returns that are stochastically dominated by the objective distribution of these returns. The subjective distribution is characterized by doubt if it is a mean-preserving spread of the objective distribution. This note offers a decision theoretic foundation of Abel's ad-hoc definitions of pessimism and doubt under the assumption that individuals exhibit ambiguity attitudes in the sense of Schmeidler (1989). In particular, we show that the behavior of a representative agent, who resolves her uncertainty with respect to the true distribution of asset returns in a pessimistic way, is the equivalent to pessimism in Abel's sense. Furthermore, a representative agent, who takes into account pessimistic as well as optimistic considerations, may result in the equivalent to doubt in Abel's sense.

Ambiguity and macroeconomics:a rationale for price stickiness

This paper deals with the emergence of price stickiness, that is nominal price elasticity below one, in the wake of nominal shocks. The setting of analysis is a general equilibrium model with both ambiguity and rational expectations. Ambiguity and macroeconomics are linked exploiting a micro-founded framework. Ambiguity concerns the lack of knowledge of firms about the relationship between changes in the aggregated stock of money and in the money distribution across heterogeneous consumers in the economy. Ambiguity is represented through a multiple priors approach. It is shown that price stickiness can emerge even if a change in the money supply level does not alter the distribution of money across consumers (uniform monetary policy). The key assumption made in the paper is that attitude towards ambiguity of firms is asymmetric: ambiguity aversion towards uncertain positive outcomes (gains) and ambiguity seeking towards negative outcomes (losses). By focusing on the dynamics of beliefs following a change in the stock of money that does not alter the money distribution, it is shown that money neutrality remains true in the long runAmbiguity, multiple priors, incomplete information, price stickiness

Comonotonic Book-Making with Nonadditive Probabilities

This paper shows how de Finetti's book-making principle, commonly used to justify additive subjective probabilities, can be modi-ed to agree with some nonexpected utility models.More precisely, a new foundation of the rank-dependent models is presented that is based on a comonotonic extension of the book-making principle.The extension excludes book-making only if all gambles considered induce a same rank-ordering of the states of nature through favorableness of their associated outcomes, and allows for nonadditive probabilities.Typical features of rank-dependence, hedging, ambiguity aversion, and pessimism and optimism, can be accommodated.Book-making;comonotonic;Choquet expected utility;ambiguity aversion;ordered vector space

Rational expectations and ambiguity: A comment on Abel (2002)

Abel (2002) proposes a resolution of the riskfree rate and the equity premium puzzles by considering pessimism and doubt. Pessimism is characterized by subjective probabilistic beliefs about consumption growth rates that are stochastically dominated by the objective distribution. The subjective distribution is characterized by doubt if it is a mean-preserving spread of the objective distribution. This note offers a decision theoretic foundation of Abel's ad-hoc definitions of pessimism and doubt under the assumption that individuals exhibit ambiguity attitudes in the sense of Schmeidler (1989). In particular, we show that the behavior of a representative agent, who resolves her uncertainty with respect to the true distribution of asset returns in a pessimistic way, is the equivalent to pessimism in Abel''s sense. Furthermore, a representative agent, who takes into account pessimistic as well as optimistic considerations, may result in the equivalent to doubt in Abel''s sense.ambiguity

Real Monetary Incentives and Chained Questions: An Experimental Study Investigating the Validity of Risk Estimates Elicited via Exchangeability Method

Risk and Uncertainty,

Investment Behavior under Ambiguity: The Case of Pessimistic Decision Makers

We define pessimistic, respectively optimistic, investors as CEU (Choquet expected utility) decision makers who update their pessimistic, respectively optimistic, beliefs according to a pessimistic (Dempster-Shafer), respectively optimistic, update rule. This paper then demonstrates that, in contrast to optimistic investors, pessimistic investors may strictly prefer investing in an illiquid asset to investing in a liquid asset. Key to our result is the dynamic inconsistency of CEU decision making, implying that a CEU decision maker ex ante prefers a different strategy with respect to prematurely liquidating an uncertain long-term investment project than after learning her liquidity needs. Investing in an illiquid asset then serves as a commitment device guaranteeing an ex ante favorable outcome.

Rational Expectations and Ambiguity: A Comment on Abel (2002)

Abel (2002) proposes a resolution of the riskfree rate and the equity premium puzzles by considering pessimism and doubt. Pessimism is characterized by subjective probabilistic beliefs about asset returns that are stochastically dominated by the objective distribution of these returns. The subjective distribution is characterized by doubt if it is a meanpreserving spread of the objective distribution. This note offers a decision theoretic foundation of Abel's ad-hoc definitions of pessimism and doubt under the assumption that individuals exhibit ambiguity attitudes in the sense of Schmeidler (1989). In particular, we show that the behavior of a representative agent, who resolves her uncertainty with respect to the true distribution of asset returns in a pessimistic way, is the equivalent to pessimism in Abel's sense. Furthermore, a representative agent, who takes into account pessimistic as well as optimistic considerations, may result in the equivalent to doubt in Abel's sense