相对财富与股票溢价之谜

Mehra和Prescott( 1 985 )提出著名的股票溢价之谜 (EquityPremiumPuzzle) :合理的相对风险规避系数 ,不能解释美国S&P5 0 0指数的收益率为什么比无风险债券的收益率高出 6个百分点。本文提出了一个基于相对财富的资产定价模型 ,其中代表性投资者的效用函数不但依赖于消费 ,还依赖于投资者的绝对财富 ,及社会平均财富。本文使用该模型 ,解释了股票溢价之谜。     

THE DEMAND FOR A RISKY ASSET: SIGNING,JOINTLY AND SEPARATELY,THE EFFECTS OF THREE DISTRIBUTIONAL SHIFTS

We show that, if an individual's utility function exhibits a degree of relative temperance smaller than one, the individual will react, in a plausible way, to each of three common shifts in the stochastic distribution of his wealth, namely to FSD shifts, mean‐preserving spreads and increases in downside risk. First, we derive, in a unified setting, necessary and sufficient conditions for signing the comparative‐static effects of each of these shifts separately, and, second, we invoke implications of the property of mixed risk aversion to merge these separate conditions into a single sufficient condition for jointly signing all comparative‐static effects.     

MONOTONICITY PROPERTIES OF OPTIMAL INVESTMENT STRATEGIES FOR LOG-BROWNIAN ASSET PRICES

Consider the geometric Brownian motion market model and an investor who strives to maximize expected utility from terminal wealth. If the investor's relative risk aversion is an increasing function of wealth, the main result in this paper proves that the optimal demand in terms of the total wealth invested in a given risky portfolio at any date is decreasing in absolute value with wealth. The proof depends on the functional form of the Brunn–Minkowski inequality due to Prékopa.     

Disappointment aversion equilibrium in a futures market

This article examines the effect of disappointment aversion on the equilibrium in a commodity futures market. Consider a commodity market with a producer and a speculator. We show that the equilibrium price is positively related to either agent's risk or disappointment aversion, and to the market volatility. The market trading volume is positively related to the producer's risk or disappointment aversion, but negatively related to the speculator's risk or disappointment aversion. The producer lowers his or her reference point in response to an increase in the risk aversion or disappointment aversion of either agent, and to an increase in spot price volatility. The speculator raises his or her reference point when the producer becomes more risk averse or disappointment averse, or when the spot price becomes more volatile. A more disappointment‐averse speculator will lower his or her reference point. However, a more risk‐averse speculator raises (lowers) the reference point if he or she is less (more) risk averse than the producer. Numerical examples are provided to further support the above analytical results. © 2003 Wiley Periodicals, Inc. Jrl Fut Mark 23:135–150, 2003     

Equilibrium investment with random risk aversion

We solve the problem of an investor who maximizes utility but faces random preferences. We propose a problem formulation based on expected certainty equivalents. We tackle the time-consistency issues arising from that formulation by applying the equilibrium theory approach. To this end, we provide the proper definitions and prove a rigorous verification theorem. We complete the calculations for the cases of power and exponential utility. For power utility, we illustrate in a numerical example that the equilibrium stock proportion is independent of wealth, but decreasing in time, which we also supplement by a theoretical discussion. For exponential utility, the usual constant absolute risk aversion is replaced by its expectation.     

MISUSE AND OPTIMUM INSPECTING STRATEGY IN AGENCY PROBLEMS

Assets misuse by an agent and the optimal audit inspecting strategy are analyzed in this paper. The agent and the principal are acting to maximize their expected utility and both are characterized by risk aversion. The agent's decision about a theft takes into account the probability of benefiting from the stolen assets but also the probability of being penalized if caught. The principal's decision about the optimal number of audit teams, hence, the probability of uncovering the theft, takes into account the cost involved, the probability of one team of auditors uncovering the theft and the agent's decision about the theft. We get two response curves which describe the optimal behavior of both the agent and the principal and show that there may be a Nash solution to the problem. Since in real life there are often many principals (shareholders) with different utility functions, a set of efficient strategies is offered using the First and Second degree Stochastic Dominance rules. A numerical illustration which clarifies the methodology and displays the applicability of the model is also provided.     

CEO's Total Wealth Characteristics and Implications on Firm Risk

We study the connections between firm risk and the CEO's personal wealth characteristics, using a unique dataset on CEO wealth and its components. Consistent with decreasing absolute risk aversion, we find that wealthier CEOs are associated with higher risk firms. Riskier firms tend to have CEOs whose wealth is more independent of the firm. We also find that CEOs with high personal portfolio betas run firms with higher betas. CEO's tenure is negatively associated with firm risk measured either as beta, idiosynchratic risk, or volatility of accounting profitability. A possible interpretation is that risk‐averse managers are better able to imprint their risk preferences on the firm over time. Stronger corporate governance weakens the connection between CEO wealth characteristics and firm risk.     

OPTIMAL TIMING FOR AN INDIVISIBLE ASSET SALE

In this paper, we investigate the pricing via utility indifference of the right to sell a non‐traded asset. Consider an agent with power utility who owns a single unit of an indivisible, non‐traded asset, and who wishes to choose the optimum time to sell this asset. Suppose that this right to sell forms just part of the wealth of the agent, and that other wealth may be invested in a complete frictionless market. We formulate the problem as a mixed stochastic control/optimal stopping problem, which we then solve. We determine the optimal behavior of the agent, including the optimal criteria for the timing of the sale. It turns out that the optimal strategy is to sell the non‐traded asset the first time that its value exceeds a certain proportion of the agent's trading wealth. Further, it is possible to characterize this proportion as the solution to a transcendental equation.     

MEAN–VARIANCE PORTFOLIO OPTIMIZATION WITH STATE‐DEPENDENT RISK AVERSION

The objective of this paper is to study the mean–variance portfolio optimization in continuous time. Since this problem is time inconsistent we attack it by placing the problem within a game theoretic framework and look for subgame perfect Nash equilibrium strategies. This particular problem has already been studied in Basak and Chabakauri where the authors assumed a constant risk aversion parameter. This assumption leads to an equilibrium control where the dollar amount invested in the risky asset is independent of current wealth, and we argue that this result is unrealistic from an economic point of view. In order to have a more realistic model we instead study the case when the risk aversion depends dynamically on current wealth. This is a substantially more complicated problem than the one with constant risk aversion but, using the general theory of time‐inconsistent control developed in Björk and Murgoci, we provide a fairly detailed analysis on the general case. In particular, when the risk aversion is inversely proportional to wealth, we provide an analytical solution where the equilibrium dollar amount invested in the risky asset is proportional to current wealth. The equilibrium for this model thus appears more reasonable than the one for the model with constant risk aversion.     

Trading under the proof-of-stake protocol – A continuous-time control approach

We develop a continuous-time control approach to optimal trading in a Proof-of-Stake (PoS) blockchain, formulated as a consumption-investment problem that aims to strike the optimal balance between a participant's (or agent's) utility from holding/trading stakes and utility from consumption. We present solutions via dynamic programming and the Hamilton–Jacobi–Bellman (HJB) equations. When the utility functions are linear or convex, we derive close-form solutions and show that the bang-bang strategy is optimal (i.e., always buy or sell at full capacity). Furthermore, we bring out the explicit connection between the rate of return in trading/holding stakes and the participant's risk-adjusted valuation of the stakes. In particular, we show when a participant is risk-neutral or risk-seeking, corresponding to the risk-adjusted valuation being a martingale or a sub-martingale, the optimal strategy must be to either buy all the time, sell all the time, or first buy then sell, and with both buying and selling executed at full capacity. We also propose a risk-control version of the consumption-investment problem; and for a special case, the “stake-parity” problem, we show a mean-reverting strategy is optimal.     

Generalized Ordered Weighted Reference Dependent Utility Aggregation Operators and Their Applications to Group Decision-Making

To quantify the influence of decision makers’ psychological factors on the group decision process, this paper develops a new class of aggregation operators based on reference-dependent utility functions (RUs) in multi-attribute group decision analysis. RUs include S-shaped RU and non-S-shaped RU. Each RU affords a framework where the psychological factors explicitly enter the decision problem via the basic utility function, reference point and loss aversion coefficient. Under the general framework, we derive a generalized ordered weighted S-shaped RU proportional averaging (GOSP) operator and a generalized ordered weighted non-S-shaped RU proportional averaging (GONSP) operator, respectively. The GOSP operator implies the risk attitude of the DM for relative losses is risk-seeking, while GONSP operator indicates the risk attitude in this case is risk-averse. As a special case, GONSP operator can degenerate into GOWPA operator which means that the attitude of the DM is risk-neutral. Each operator satisfies the desirable properties of general operator, i.e., monotonicity, commutativity, idempotency and boundedness. Furthermore, we consider hyperbolic absolute risk aversion (HARA) function as the basic utility function, and define an S-shaped HARA and a non-S-shaped HARA utility functions. Based on the two new RUs, we propose GOSP–HARA operator and GONSP–HARA operator. Every operator covers many existing aggregation operators. To ascertain weights of such operators, the paper builds an attribute-deviation weight model and a DMs-deviation weight model. Based on these RU operators and weight models, an approach is addressed for solving multiple attribute group decision-making problem. At last, an example is provided to show the feasible of our approach.     

Convex duality for Epstein–Zin stochastic differential utility

This paper introduces a dual problem to study a continuous‐time consumption and investment problem with incomplete markets and Epstein–Zin stochastic differential utilities. Duality between the primal and dual problems is established. Consequently, the optimal strategy of this consumption and investment problem is identified without assuming several technical conditions on market models, utility specifications, and agent's admissible strategies. Meanwhile, the minimizer of the dual problem is identified as the utility gradient of the primal value and is economically interpreted as the “least favorable” completion of the market.     

Robust consumption‐investment problem under CRRA and CARA utilities with time‐varying confidence sets

We consider a robust consumption‐investment problem under constant relative risk aversion and constant absolute risk aversion utilities. The time‐varying confidence sets are specified by Θ, a correspondence from [0, T] to the space of the Lévy triplets, and describe a priori drift, volatility, and jump information. For each possible measure, the log‐price processes of stocks are semimartingales, and the triplet of their differential characteristics is almost surely a measurable selector from the correspondence Θ. By proposing and investigating the global kernel, an optimal policy and a worst‐case measure are generated from a saddle point of the global kernel, and they constitute a saddle point of the objective function.     

Convergence of utility indifference prices to the superreplication price in a multiple‐priors framework

This paper formulates a utility indifference pricing model for investors trading in a discrete time financial market under nondominated model uncertainty. Investor preferences are described by possibly random utility functions defined on the positive axis. We prove that when the investors's absolute risk aversion tends to infinity, the multiple‐priors utility indifference prices of a contingent claim converge to its multiple‐priors superreplication price. We also revisit the notion of certainty equivalent for multiple‐priors and establish its relation with risk aversion.     

Shortfall aversion

Shortfall aversion reflects the higher utility loss of spending cuts from a reference than the utility gain from similar spending increases. Inspired by Prospect Theory's loss aversion and the peak‐end rule, this paper posits a model of utility from spending scaled by past peak spending. In contrast to traditional models, which call for spending rates proportional to wealth, the optimal policy in this model implies a constant spending rate equal to the historical peak when wealth is relatively large. The spending rate increases when wealth reaches a model‐determined multiple of peak spending. In 1926–2015, shortfall‐averse spending is smooth and typically increasing.     

MULTIDIMENSIONAL PORTFOLIO OPTIMIZATION WITH PROPORTIONAL TRANSACTION COSTS

We provide a computational study of the problem of optimally allocating wealth among multiple stocks and a bank account, to maximize the infinite horizon discounted utility of consumption. We consider the situation where the transfer of wealth from one asset to another involves transaction costs that are proportional to the amount of wealth transferred. Our model allows for correlation between the price processes, which in turn gives rise to interesting hedging strategies. This results in a stochastic control problem with both drift-rate and singular controls, which can be recast as a free boundary problem in partial differential equations. Adapting the finite element method and using an iterative procedure that converts the free boundary problem into a sequence of fixed boundary problems, we provide an efficient numerical method for solving this problem. We present computational results that describe the impact of volatility, risk aversion of the investor, level of transaction costs, and correlation among the risky assets on the structure of the optimal policy. Finally we suggest and quantify some heuristic approximations.     

OPTIMAL INVESTMENT WITH AN UNBOUNDED RANDOM ENDOWMENT AND UTILITY-BASED PRICING

This paper studies the problem of maximizing the expected utility of terminal wealth for a financial agent with an unbounded random endowment, and with a utility function which supports both positive and negative wealth. We prove the existence of an optimal trading strategy within a class of permissible strategies—those strategies whose wealth process is a super-martingale under all pricing measures with finite relative entropy. We give necessary and sufficient conditions for the absence of utility-based arbitrage, and for the existence of a solution to the primal problem. We consider two utility-based methods which can be used to price contingent claims. Firstly we investigate marginal utility-based price processes (MUBPP's). We show that such processes can be characterized as local martingales under the normalized optimal dual measure for the utility maximizing investor. Finally, we present some new results on utility indifference prices, including continuity properties and volume asymptotics for the case of a general utility function, unbounded endowment and unbounded contingent claims.     

Entrepreneurship and Risk Aversion

Evans and Jovanovic (1989, Journal of Political Economy 97(4), 808–827) find that wealth is an important determinant of business startups due to liquidity constraints. However, Cressy (2000, Economic Letters 66, 235–240) argues that if risk aversion is a negative function of wealth, Evans and Jovanovic’s empirical results could be spurious and the positive effect of wealth could be due to the omission of risk aversion in the regression equation. In other words, according to Cressy, one’s wealth does not have any effect on business startups once the degree of risk aversion is accounted for. This paper attempts to investigate the validity of Cressy’s conjecture. We empirically examine the effect of wealth on the transition into self-employment, while allowing for the effect of risk aversion. Our empirical findings show that Evans and Jovanovic’s (1989) results are robust, i.e., wealth has a positive effect on business startups even allowing for the confounding effects of risk aversion.     

Hedging nontradable risks with transaction costs and price impact

A risk‐averse agent hedges her exposure to a nontradable risk factor U using a correlated traded asset S and accounts for the impact of her trades on both factors. The effect of the agent's trades on U is referred to as cross‐impact. By solving the agent's stochastic control problem, we obtain a closed‐form expression for the optimal strategy when the agent holds a linear position in U. When the exposure to the nontradable risk factor is nonlinear, we provide an approximation to the optimal strategy in closed‐form, and prove that the value function is correctly approximated by this strategy when cross‐impact and risk‐aversion are small. We further prove that when is nonlinear, the approximate optimal strategy can be written in terms of the optimal strategy for a linear exposure with the size of the position changing dynamically according to the exposure's “Delta” under a particular probability measure.     

Dividend policy and capital structure of a defaultable firm

Default risk significantly affects the corporate policies of a firm. We develop a model in which a limited liability entity subject to default at an exponential random time jointly sets its dividend policy and capital structure to maximize the expected lifetime utility from consumption of risk‐averse equity investors. We give a complete characterization of the solution to the singular stochastic control problem. The optimal policy involves paying dividends to keep the ratio of firm's equity value to investors' wealth below a critical threshold. Dividend payout acts as a precautionary channel to transfer wealth from the firm to investors for mitigation of losses in the event of default. Higher the default risk, more aggressively the firm leverages and pays dividends.