Decreasing downside risk aversion and background risk

In this paper, we show that risk vulnerability can be associated with the concept of downside risk aversion (DRA) and an assumption about its behavior, namely that it is decreasing in wealth. Specifically, decreasing downside risk aversion in the Arrow–Pratt and Ross senses are respectively necessary and sufficient for a zero-mean background risk to raise the aversion to other independent risks.     

Comparative Ross risk aversion in the presence of mean dependent risks

This paper studies comparative risk aversion between risk averse agents in the presence of a background risk. Our contribution differs from most of the literature in two respects. First, background risk does not need to be additive or multiplicative. Second, the two risks are not necessarily mean independent, and may be conditional expectation increasing or decreasing. We show that our order of cross Ross risk aversion is equivalent to the order of partial risk premium, while our index of decreasing cross Ross risk aversion is equivalent to decreasing partial risk premium. These results generalize the comparative risk aversion model developed by Ross for mean independent risks. Our theoretical results are related to utility functions having the n-switch independence property.     

Necessity of hyperbolic absolute risk aversion for the concavity of consumption functions

Carroll and Kimball (1996) have shown that, in the class of utility functions that are strictly increasing, strictly concave, and have nonnegative third derivatives, hyperbolic absolute risk aversion (HARA) is sufficient for the concavity of consumption functions in general consumption-saving problems. This paper shows that HARA is necessary, implying the concavity of consumption is not a robust prediction outside the HARA class.     

Dilatation monotonous Choquet integrals

Choquet integrals allow to define the utility, respectively a risk-adjusted value, of a bounded random payment, or alternatively a (coherent) risk measure by changing the sign. We show that a necessary and sufficient condition for dilatation monotonicity of a Choquet integral is the convexity of the corresponding capacity with respect to the underlying probability measure. It follows that utility functionals with respect to a Choquet integral are dilatation monotonous iff the defining Choquet integral is dilatation monotonous.     

Dilatation monotonous Choquet integrals

Choquet integrals allow to define the utility, respectively a risk-adjusted value, of a bounded random payment, or alternatively a (coherent) risk measure by changing the sign. We show that a necessary and sufficient condition for dilatation monotonicity of a Choquet integral is the convexity of the corresponding capacity with respect to the underlying probability measure. It follows that utility functionals with respect to a Choquet integral are dilatation monotonous iff the defining Choquet integral is dilatation monotonous.     

Financial risk taking in the presence of correlated non-financial background risk

This paper characterizes the stochastic deterioration resulting from taking a zero-mean financial risk in the presence of correlated non-financial background risk. We show in particular that it has an equivalent stochastic order as well as a necessary and sufficient “integral condition” that implies and is implied by a particular sense in which the stochastic deterioration can be decomposed into a “correlation increase” and a “marginal risk increase”. We further characterize a measure of aversion to the stochastic deterioration. These characterizations provide for a more general framework for formulating concepts of increases in risk and correlation and for better understanding risk management decisions governed by individuals’ attitudes to them.     

Tempering effects of (dependent) background risks: A mean-variance analysis of portfolio selection

In a mean variance framework, we analyse risk taking in the presence of a (possibly) dependent background risk, exemplified in a linear portfolio selection problem. We first characterise the comparative statics of changes in the distribution and dependence structure of the background risk. For unfair, undesirable and loss-aggravating increases in background risks (both dependent and independent), we then present necessary and sufficient restrictions on preferences such that greater background uncertainty leads to reduced risk taking. With mean-variance preferences, these restrictions boil down to simple conditions on the marginal rate of substitution between risk and return. They can be easily related to familiar notions such as risk vulnerability, properness or standardness.     

Nonrecursive separation of risk and time preferences

Recursive utility disentangles preferences with respect to time and risk by recursively building up a value function of local increments. This involves certainty equivalents of indirect utility. Instead we disentangle preferences with respect to time and risk by building up a value function as a non-linear aggregation of certainty equivalents of direct utility of consumption. This entails time-consistency issues which are dealt with by looking for an equilibrium control and an equilibrium value function rather than a classical optimal control and a classical optimal value function. We characterize the solution in a general diffusive incomplete market model and find that, in certain special cases of utmost interest, the characterization coincides with what would arise from a recursive utility approach. But also importantly, in other cases, it does not: The two approaches are fundamentally different but match, exclusively but importantly, in the mathematically special case of homogeneity of the value function.     

When Ross meets Bell: The linex utility function

At first glance, there would appear to be no relationship between Bell’s (1988) concept of one-switch utility functions and that of a stronger measure of risk aversion due to Ross (1981). We show however that specific assumptions about the behavior of the stronger measure of risk aversion also give rise to the linex utility function which belongs to the class of one-switch utility functions. In particular, this utility class is the only one that satisfies a stronger version of Kimball’s (1993) standard risk aversion over all levels of wealth. We apply our results to consider n$n$th-degree deteriorations in background risk and their effect on risk taking behavior.     

Prediction market prices under risk aversion and heterogeneous beliefs

In this paper, we examine the properties of prediction market prices when risk averse traders have heterogeneous beliefs in state probabilities. We show that the equilibrium state prices equal the mean beliefs of traders about that state if and only if the traders’ common utility function is logarithmic. We also provide a necessary and sufficient condition ensuring that the state prices are systematically below or above the mean beliefs of traders, thus providing a rational explanation to the favorite-longshot bias in prediction markets.     

Risk aversion for variational and multiple-prior preferences

The objective of this paper is to identify variational preferences and multiple-prior (maxmin) expected utility functions that exhibit aversion to risk under some probability measure from among the priors. Risk aversion has profound implications on agents’ choices and on market prices and allocations. Our approach to risk aversion relies on the theory of mean-independent risk of Werner (2009). We identify necessary and sufficient conditions for risk aversion of convex variational preferences and concave multiple-prior expected utilities. The conditions are stability of the cost function and of the set of probability priors, respectively, with respect to a probability measure. The two stability properties are new concepts. We show that cost functions defined by the relative entropy distance or other divergence distances have that property. Set of priors defined as cores of convex distortions of probability measures or neighborhoods in divergence distances have that property, too.     

Rationalizing investors’ choices

Assuming that agents’ preferences satisfy first-order stochastic dominance, we show how the Expected Utility paradigm can rationalize all optimal investment choices: the optimal investment strategy in any behavioral law-invariant (state-independent) setting corresponds to the optimum for an expected utility maximizer with an explicitly derived concave non-decreasing utility function. This result enables us to infer the utility and risk aversion of agents from their investment choice in a non-parametric way. We relate the property of decreasing absolute risk aversion (DARA) to distributional properties of the terminal wealth and of the financial market. Specifically, we show that DARA is equivalent to a demand for a terminal wealth that has more spread than the opposite of the log pricing kernel at the investment horizon.     

Optimal risk taking in an uneven tournament game with risk averse players

We analyze the optimal choice of risk in a two-stage tournament game between two players that have different concave utility functions. At the first stage, both players simultaneously choose risk. At the second stage, both observe overall risk and simultaneously decide on effort or investment. The results show that those two effects which mainly determine risk taking – an effort effect and a likelihood effect – are strictly interrelated. This finding sharply contrasts with existing results on risk taking in tournament games with symmetric equilibrium efforts where such linkage can never arise. Conditions are derived under which this linkage leads to a reversed likelihood effect so that the favorite (underdog) can increase his winning probability by increasing (decreasing) risk which is impossible in a completely symmetric setting.     

Is insurance normal or inferior? -A regret theoretical approach-

This study considers how changes in wealth affect insurance demand when individuals suffer disutility from regret. Anticipated regret stems from a comparison between the ex-post maximum and actual wealth. We consider a situation wherein individuals maximize their expected utility incorporating anticipated regret. The wealth effect on insurance demand can be classified into the risk and the regret effects. These effects are determined by the properties of the utility function and the regret function. We show that insurance can be normal when individuals place weight on anticipated regret, even though the utility function exhibit decreasing absolute risk aversion. This result indicates that regret theory is a possible explanation to the wealth effect puzzle, in which insurance is normal from empirical observation, but it should be inferior by theoretical prediction under expected utility theory.     

Duality and consumption decisions under income and price risk

This paper uses duality to provide an analysis of compensated and uncompensated decisions under income and/or price risk. We focus on a two-good model, in which the individual maximizes expected utility subject to a stochastic budget constraint. A Slutsky equation is derived that decomposes the derivative of the optimal decision function with respect to any parameter in the model into an income effect and a substitution effect. The total effect of an increase in risk is controlled by the generalized preference intensity, while the compensated effect of an increase in risk is controlled by the generalized risk premium developed in the literature on aversion to one risk in the presence of another.     

Ordering utility functions based on mean-seeking behavior1

We consider utility function partial orderings to predict comparative portfolio features with two risky assets. No utility ordering can predict comparative holdings of the riskier asset for any reasonable definition of the latter. We thus reinterpret results of Arrow-Pratt and Ross as predicting comparative mean-seeking behavior. We also present a stronger utility ordering which predicts comparative portfolio means with no joint distribution restrictions. Thus we present a progression of contexts, with successively more relaxed distributional restrictions and hence successively stronger restrictions on utility function pairs, in which comparative mean-seeking behavior (not comparative risk avoidance) is predictable.     

Efficient allocations and equilibria with short-selling and incomplete preferences

This paper reconsiders the theory of existence of efficient allocations and equilibria when consumption sets are unbounded below under the assumption that agents have incomplete preferences. Our model is motivated by an example in the theory of assets with short-selling where there is risk and ambiguity. Agents have Bewley’s incomplete preferences. As an inertia principle is assumed in markets, equilibria are individually rational. It is shown that a necessary and sufficient condition for the existence of an individually rational efficient allocation or of an equilibrium is that the relative interiors of the risk adjusted sets of probabilities intersect. The more risk averse, the more ambiguity averse the agents, the more likely is an equilibrium to exist. The paper then turns to incomplete preferences represented by a family of concave utility functions. Several definitions of efficiency and of equilibrium with inertia are considered. Sufficient conditions and necessary and sufficient conditions are given for the existence of efficient allocations and equilibria with inertia.     

Intensity of preferences for bivariate risk apportionment

Bivariate risk apportionment is the preference for dispersing risks associated with two aspects of individuals’ well-being into different states of the world. In this paper, we propose an intensity measure of this preference by extending to the bivariate case the concept of marginal rate of substitution between risks of different orders introduced in the univariate case by Liu and Meyer (2013). We show that the intensity measure of the preference for bivariate risk apportionment is characterized by bivariate risk attitudes in the sense of Ross. The usefulness of our measures to understand economic choices is illustrated by the analysis of two specific decisions: savings under environmental risk and medical treatment in the presence of diagnostic risks.     

Risk aversion and risk vulnerability in the continuous and discrete case

This paper discusses utility functions for money, where allowable money values are from an arbitrary nonempty closed subset of the real numbers. Thus, the classical case, where this subset is a closed interval (bounded or not) of the real line, is included in the study. The discrete case, where this subset is the set of all integer numbers, is also included. In a sense, the discrete case (which has not been addressed in the literature thus far) is more suitable for real-world applications than the continuous case. In this general setting, the concepts of risk aversion and risk premium are defined, an analogue of Pratt’s fundamental theorem is proved, and temperance, prudence, and risk vulnerability are examined.     

Axiomatization of weighted (separable) utility

Nontrivial decision problems typically involve a trade-off among multiple attributes of choice options. One simple way of resolving such trade-offs is to aggregate multiple attributes into one real-valued index, known as weighted or separable utility. Applications of weighted utility can be found in choice under risk (expected utility) and uncertainty (subjective expected utility), intertemporal choice (discounted utility) and welfare economics (utilitarian social welfare function). This paper presents an alternative behavioral characterization (preference axiomatization) of weighted utility. It is shown that necessary and sufficient conditions for weighted utility are completeness, continuity, bi-separable transitivity (and transitivity if none of the attributes is null, or inessential).