A Definition of Uncertainty Aversion

A definition of uncertainty or ambiguity aversion is proposed. It is argued that the definition is well-suited to modelling within the Savage (as opposed to Anscombe and Aumann) domain of acts. The defined property of uncertainty aversion has intuitive empirical content, behaves well in specific models of preference (multiple-priors and Choquet expected utility) and is tractable. Tractability is established through use of a novel notion of differentiability for utility functions, called eventwise differentiability.     

Preservation of “more risk averse” under expectations

The preservation of risk aversion properties of utility functions under expectation operations is of interest in the study of derived utility functions in sequential decision problems and in problems with multiple (contemporaneous) sources of uncertainty. The purpose of this note is to present sufficient conditions for the Pratt relation “more risk averse” to be preserved under expectations.     

On the structure of Ramsey equilibrium: Cycles,indeterminacy, and sunspots

Summary We consider a one-sector neoclassical capital accumulation model under borrowing constraints with infinitely-lived heterogeneous households. Under the standard assumptions of strictly concave and time-additive utility functionals and a strictly concave production function we show that perfect foresight equilibria can be non-unique, even locally non-unique (indeterminate), and periodic of arbitrary long periodp. Moreover, we prove that there can exist non-trivial rational expectations (sunspot) equilibria when the agent's expectations about future factor prices depend on extrinsic uncertainty.Remarks made by an anonymous referee were extremely helpful in preparing the final draft of this paper.     

Stationary cardinal utility and optimal growth under uncertainty

In the literature on multiperiod planning under uncertainty, it is generally postulated that preferences may be represented by a von Neumann-Morgenstern utility index that is additive over time. This paper accomplishes two objectives: First, an axiomatic basis is provided for a more general class of non-additive utility indices defined over infinite consumption streams. Second, this class of utility functions is applied to extend existing results (J. Econ. Theory4 (1972), 479–513; J. Econ. Theory11 (1975), 329–339) on the nature of optimal growth under uncertainty. Of particular interest are the existence and stability of a stochastic steady state.     

Knightian uncertainty and poverty trap in a model of economic growth

This paper explores how Knightian uncertainty affects dynamic properties in an economic growth model. The decision-making theory employed in the analysis is the theory of expected utility under a non-additive probability measure, i.e., the Choquet expected utility model of preference. We apply this decision-making theory to an overlapping generations model where producers face “uncertainty” in their technologies. When the producer is averse to uncertainty, the firm's profit function may not be differentiable. Therefore, the firm's decision to invest and hire labor becomes rigid for a certain measurable range of real interest rates. In dynamic equilibrium, the existence of firm-level rigidity causes discontinuity in the wage function; this makes multiple equilibria the more likely outcomes under the log utility and Cobb–Douglas production functions. In this paper, we show that even if aversion to uncertainty is small, the “poverty trap” can arise for a wide range of parameter values.     

Optimal consumption under income uncertainty: An example and a conjecture

This paper demonstrates that, under certain circumstances, the optimal consumption strategy of an individual with constant absolute risk-aversion, facing income uncertainty, is linear in wealth. Comparative static results are derived, and the paper concludes with a conjecture about other classes of utility functions.     

Risk preference and productivity measurement under output price uncertainty

This paper deals with joint estimation of production and risk preference functions in the presence of output price uncertainty. We use quadratic production and utility functions under the assumption that producers maximize expected utility of anticipated profit. A panel data on Norwegian salmon farms is used for this purpose. Empirical results show that all salmon farmers are risk averse. Relative risk premium (the implicit cost of private risk bearing) is found to be about 15% of mean profit. We also find rapid technological change taking place (3.75% per year) in the salmon farming industry. First version received: February 2000/Final version received: February 2001     

Compatibility of expected utility and <Emphasis Type="Italic">μ/σ</Emphasis> approaches to risk for a class of non location–scale distributions

Proofs of compatibility of the expected utility and μ/σ approaches to incorporating uncertainty in decision making exist for at least some utility functions and location–scale distributions. But there are severe constraints and it is desirable to investigate compatibility more widely. We do so for the class of distributions that are transformable to location–scale form by concave transformation and where the utility functions remain concave under transformation. The class is important, containing distributions such as the lognormal and Pareto, usually considered more appropriate for modelling income or wealth than those in the location–scale family. We are grateful to Jack Meyer for very helpful comments and discussions and also to an anonymous referee for useful remarks.     

Achieving efficiency with manipulative bargainers

Two agents bargain over the allocation of a bundle of divisible commodities. After strategically reporting utility functions to a neutral arbitrator, the outcome is decided by using a bargaining solution concept chosen from a family that includes the Nash and the Raiffa–Kalai–Smorodinsky solutions. When reports are restricted to be continuous, strictly increasing and concave, it has been shown that this kind of “distortion game” leads to inefficient outcomes. We study the distortion game originated when agents are also allowed to claim non-concave utility functions. Contrasting with the previous literature, any interior equilibrium outcome is efficient and any efficient allocation can be supported as an equilibrium outcome of the distortion game. In a similar fashion to the Nash demand game we consider some uncertainty about the opponent's features to virtually implement the Nash bargaining solution.     

On Professor Kohn and Expected Utility: Correction and Clarification-Rejoinder

Professor Horowitz correctly identifies the limitation of my assuming separable utility functions to derive a marginal condition for efficiency under uncertainty. Correction this limitation, he provides a simple but powerful condition that encompasses the nonseparable as well as the separable case. This condition replaces the dubious Equation (14) derived in Kohn (1999). In a departure from von Neumann-Morgenstern theory, for cases in which the decisions of a risk-averse community are compared with those it would make were it risk-neutral, it is proposed here that the same utility function holds for risk-neutrality as for risk-aversion, but that the stochastic quantities be replaced by their expected value in the former. [Q25]     

On the theory of the competitive firm with a utility function defined on profits and regret

In this paper we analyze the optimal output determined by a competitive firm facing uncertain demand. We analyze the effect of introducing uncertainty and the effect of increasing uncertainty on the optimal output, under the assumption that the utility function of the firm depends both on profits and on regret. We show that if the firm is more risk averse to profits than to regret (in a sense described below), both effects tend to decrease the optimal output. Similar effects of introducing uncertainty and of increased uncertainty were previously shown by Sandmo (1971) to exist in the case where utility is defined on profits only. Thus, this paper provides conditions under which the above results hold true, even when utility is defined on regret and on profits.     

On the existence of optimal processes in non-stationary environments

We consider an aggregative model of intertemporal allocation under uncertainty, in which the utility and production functions are allowed to be time dependent, the random shocks occurring in each period are entirely arbitrary, and the production functions are permitted to be non-concave. In this framework, we provide a theorem on the existence of infinite-horizon optimal processes. In the course of establishing this result, we obtain the existence of optimal policy functions and we show that they are monotone in the stock levels.This paper has benefitted from the comments of two referees of the journal. Research of the first author was supported by a National Science Foundation Grant.     

Optimal consumption and the timing of the resolution of uncertainty

As is well-known, consumers want to accumulate precautionary savings in the face of income risks when their marginal utility is convex (prudence). In this paper, we explore the effect of the timing of the resolution of income uncertainty on savings. An agent faces uncertainty about his income at date t+2. What is the effect of being informed that the uncertainty will be resolved at date t+1 on the consumption at date t? We show that the effect is positive, if and only if, marginal utility is convex (prudence), when either the risk free rate is equal to the rate of pure preference for the present, or when the utility function is HARA. The intuition is that an early resolution of uncertainty allows for time-diversifying the risk. It therefore plays a role similar to a reduction of the income risk, whose effect on savings is negative under prudence.     

Risk and risk aversion when states of nature matter

When uncertainty is associated with some intrinsically relevant states of nature, there is no reason for an agent to base his or her preferences only on probability distribution of claims. We propose a new concept of risk for state-contingent claims that, unlike the standard concept of Rothschild–Stiglitz, does not identify state-contingent claims with their probability distribution. This concept is called mean-independent risk, and we provide a simple characterization in terms of marginal utilities of (non-expected) utility functions that exhibit aversion to mean-independent risk. We study implications of aversion to mean-independent risk on agents’ choices under uncertainty. This research has been supported by the NSF under Grant SES-0099206. I have benefited from numerous conversations with Rose-Anne Dana and illuminating discussions with Tadeusz Miłosz about the theory of subgradients.     

HETEROGENEOUS RISK ATTITUDES IN A CONTINUOUS‐TIME MODEL*

We prove that every continuous‐time model in which all consumers have time‐homogeneous and time‐additive utility functions and share a common probabilistic belief and a common discount rate can be reduced to a static model. This result allows us to extend some of the existing results of the representative consumer and risk‐sharing rules in static models to continuous‐time models. We show that the equilibrium interest rate is lower and more volatile than in the standard representative consumer economy, and that the individual consumption growth rates are more dispersed than in the absence of uncertainty.     

Preservation and exogenous uncertain future preferences

Summary. We extend the Beltratti, Chichilnisky and Heal's (1993) and (1998) continuous-time stochastic dynamic framework to analyze the optimal depletion of an asset whose consumption is irreversible, in the face of uncertainty about future preferences. Their model is rather general and so the results are general qualitative theorems. We show that in some interesting cases it is possible to solve their model analytically. The cases involve constant elasticity utility functions and the assumption of a Poisson process for the evolution of preferences. Received: September 13, 1999; revised version: November 23, 1999     

Consumption and precautionary saving: An empirical analysis under both financial and environmental risks

This paper studies the empirical relationship between consumption and saving under two different sources of uncertainty: financial risk and environmental risk. The analysis is carried out using time series data for six advanced economies in the period 1965–2007.The results support the theoretical conclusions that both financial risk alone and the interaction between financial and environmental risks influence consumption. Moreover, we suggest a solution to some shortcomings which affect the empirical analysis performed with one-argument utility functions. Finally, we provide new estimates of indexes of relative risk aversion and relative prudence, as well as relative preference of environmental quality.     

ECONOMIC MODELLING OF SUICIDE UNDER INCOME UNCERTAINTY: FOR BETTER UNDERSTANDING OF MIDDLE‐AGED SUICIDE*

This paper formalises an individual's decision about suicide within a framework of lifetime utility maximisation models. This is in line with the literature on economic modelling of suicide. The novelty of the paper is to take into account income uncertainty. Income uncertainty reduces a risk‐averse individual's expected utility, making them more likely to commit suicide. On the other hand, income uncertainty creates a value to postponing suicide even when their income gets sufficiently low. This is because income uncertainty means that if things go well, they will get higher income in the future. Thus, income uncertainty has two opposite effects on suicidal behaviour. The main objective of this paper is to construct an economic model of suicide for investigating net impacts of income uncertainty on suicidal behaviour. For this purpose, it is assumed that the wage evolves according to a stochastic process. Then, the threshold wage, below which an individual commits suicide, is derived as a function of the parameters of the stochastic process assumed for the wage evolution. Impacts of changes in these parameters on the threshold wage are calculated. With the result, the paper shows how income uncertainty affects suicidal behaviour.     

Transferable utility games with uncertainty

We introduce the concept of a TUU-game, a transferable utility game with uncertainty. In a TUU-game there is uncertainty regarding the payoffs of coalitions. One out of a finite number of states of nature materializes and conditional on the state, the players are involved in a particular transferable utility game. We consider the case without ex ante commitment possibilities and propose the Weak Sequential Core as a solution concept. We characterize the Weak Sequential Core and show that it is non-empty if all ex post TU-games are convex.     

Continuous linear representability of binary relations

Summary A very general result on continuous linear representability of binary relations on topological vector spaces is presented. Applications of this result include individual decision making under uncertainty, i.e. expected utility theory and collective decision making, in particular, utilitaristic social welfare functions.Thanks are due for helpful comments to Manfred Nermuth, David Schmeidler, Antonio Villar, and anonymous referees. Financial support from the DFG under Tr 120/4-2 is gratefully acknowledged.