Illiquide Assets in der Portfoliooptimierung

When optimizing a portfolio, which comprises liquid as well as illiquid assets, under the constraint of a liquidity requirement, one has to take into account the particular characteristics of illiquid assets. Illiquid assets in this context have the constituting property that they can only be sold as a whole and – if sold on a short term basis – selling leads to losses. Performing the analysis of a single period model in a mean downside risk framework with one liquid and one illiquid asset, significant differences are proven in comparison to the results of an optimization concerning solely liquid assets. For example, although the return on assets is safe in the first scenario, the portfolio value is already risky due to the uncertain liquidity requirement and situations arise where the allocation to both the liquid and the illiquid asset is optimal. Furthermore, when asset returns are uncertain, the expected portfolio value depends on the assets’ variances and can even be increased by positive correlations.     

Designing Supply Contracts Considering Profit Targets and Risk

Managers at all stages of a supply chain are concerned about meeting profit targets. We study contract design for a buyer–supplier supply chain, with each party maximizing expected profit subject to a chance constraint on meeting his respective profit target. We derive the optimal contract form (across all contract types) with randomized and deterministic payments. The best contract has the property that, if the chance constraints are binding, at most one party fails to satisfy his profit target for any given demand realization. This implies that “least risk sharing,”that is, minimizing the probability of outcomes for which both parties fail to achieve their profit targets, is optimal, contrary to the usual expectations of “risk sharing.” We show that an optimal contract can possess only two of the following three properties simultaneously: (i) supply chain coordination, (ii) truth‐telling, and (iii) non‐randomized payments. We discuss methods to mitigate the consequent implementation challenges. We also derive the optimal contract form when chance constraints are incorporated into several simpler and easier‐to‐implement contracts. From a numerical study, we find that an incremental returns contract (in which the marginal rebate rate depends on the return quantity) performs quite well across a relatively broad range of conditions.     

Risk‐Based Sampling: I Don't Want to Weight in Vain

Recently, there has been considerable interest in developing risk‐based sampling for food safety and animal and plant health for efficient allocation of inspection and surveillance resources. The problem of risk‐based sampling allocation presents a challenge similar to financial portfolio analysis. Markowitz (1952) laid the foundation for modern portfolio theory based on mean‐variance optimization. However, a persistent challenge in implementing portfolio optimization is the problem of estimation error, leading to false “optimal” portfolios and unstable asset weights. In some cases, portfolio diversification based on simple heuristics (e.g., equal allocation) has better out‐of‐sample performance than complex portfolio optimization methods due to estimation uncertainty. Even for portfolios with a modest number of assets, the estimation window required for true optimization may imply an implausibly long stationary period. The implications for risk‐based sampling are illustrated by a simple simulation model of lot inspection for a small, heterogeneous group of producers.     

MEASURING SELF‐CONTROL PROBLEMS: A STRUCTURAL ESTIMATION

Abstract We adopt a two‐stage Method of Simulated Moments to estimate the preference parameters in a life‐cycle consumption‐saving model augmented with temptation disutility. Our approach estimates the parameters from the comparison between simulated moments with empirical moments observed in the US Survey of Consumer Finances; to identify the parameters we consider moments from liquid and illiquid asset holdings at different ages. We find evidence of a small but significantly positive degree of temptation. The temptation model predicts consumption choices similar to the model with standard preferences, and holdings of liquid and illiquid assets closer to those observed in the empirical data.     

Dynamic Choices of Hyperbolic Consumers

Laboratory and field studies of time preference find that discount rates are much greater in the short‐run than in the long‐run. Hyperbolic discount functions capture this property. This paper solves the decision problem of a hyperbolic consumer who faces stochastic income and a borrowing constraint. The paper uses the bounded variation calculus to derive the Hyperbolic Euler Relation, a natural generalization of the standard Exponential Euler Relation. The Hyperbolic Euler Relation implies that consumers act as if they have endogenous rates of time preference that rise and fall with the future marginal propensity to consume (e.g., discount rates that endogenously range from 5% to 41% for the example discussed in the paper).     

随机跳跃幅度的最优消费与证券选择策略问题

在最优消费与证券选择问题中,假定投资市场有两种资产可供选择:一种为无风险资产(银行债券),另一种为风险资产(股票).由于受重大信息的影响,风险资产的价格往往会产生跳跃.文章研究了这种带跳跃的投资问题,用泊松过程与布朗运动模拟了投资者的财富过程.为使投资者在整个生命周期的消费效用期望值最大,在跳跃幅度为一随机变量的条件下,利用贝尔曼动态规划原理,导出了最优消费及投资策略所满足的方程组,并且在跳跃幅度的概率分布已知的情况下,针对具体的参数值,给出了最优初始策略的数值解与最大消费效用期望值.     

Liquidity in Asset Markets With Search Frictions

We develop a search‐theoretic model of financial intermediation in an over‐the‐counter market and study how trading frictions affect the distribution of asset holdings and standard measures of liquidity. A distinctive feature of our theory is that it allows for unrestricted asset holdings, so market participants can accommodate trading frictions by adjusting their asset positions. We show that these individual responses of asset demands constitute a fundamental feature of illiquid markets: they are a key determinant of trade volume, bid–ask spreads, and trading delays—the dimensions of market liquidity that search‐based theories seek to explain.     

On a neglected aspect of portfolio choice: the role of the invested capital

In return-based portfolio choice models à la Markowitz, the amount of capital invested does not play a role, while in expected utility models it does. The aim of this paper is to bring out the connection between the amount of capital invested and the portfolio formation. In a general one-period framework, which also comprises illiquid assets held by the investor and the period income, we present results in finding the optimal portfolio weights and study the influence of the invested capital, the illiquid assets and the income on the portfolio formation. Special emphasis is put on HARA utility functions and the dependence of the amount invested risklessly on the invested capital. As a side result, we find that Markowitz portfolio choice is not fully compatible with expected utility reasoning.     

RELATIVE RISK AVERSION IS CONSTANT: EVIDENCE FROM PANEL DATA

Most classical tests of constant relative risk aversion (CRRA) based on individual portfolio composition use cross‐sectional data. Such tests must assume that the distributions of wealth and preferences are independent. We use panel data to analyze how individuals’ portfolio allocation between risky and riskless assets varies in response to changes in total financial wealth. We find the elasticity of the risky asset share to wealth to be small and statistically insignificant, supporting the CRRA assumption; this finding is robust when the sample is restricted to households experiencing large income variations. In addition, we find a small but significant negative correlation between wealth and risk aversion. Various extensions are discussed.     

The Lucas Orchard

This paper investigates the behavior of asset prices in an endowment economy in which a representative agent with power utility consumes the dividends of multiple assets. The assets are Lucas trees; a collection of Lucas trees is a Lucas orchard. The model generates return correlations that vary endogenously, spiking at times of disaster. Since disasters spread across assets, the model generates large risk premia even for assets with stable cashflows. Very small assets may comove endogenously and hence earn positive risk premia even if their cashflows are independent of the rest of the economy. I provide conditions under which the variation in a small asset's price‐dividend ratio can be attributed almost entirely to variation in its risk premium.     

Shareholders' Wealth‐Maximizing Operating Decisions and Risk Management Practices in a Mixed Contracts Economy

This paper establishes a critically important positive role for operations management practices and financial hedging. We show that operations management decisions and financial hedging are intertwined, and we advance a framework that can identify their combined effects on investors' wealth. We show that: (a) firms (publicly traded corporations) will optimally hold adequate riskless working capital (e.g., cash) to minimize the cost of obtaining non‐financial inputs, and the magnitude of this cash holding depends on operating details, and (b) operations management and financial hedging can lower firms' cash requirements, and boost productivity, defined as the wealth created in the firm per dollar of invested capital. Productivity‐enhancing practices—by “freeing up” some of the firm's cash—can maximize the investors' wealth. We show that these results obtain because firms' contracts with many of the providers of non‐financial inputs are not traded, and because investors can invest not just in public corporations but also in businesses “outside the markets” (e.g., proprietorships, partnerships, and private equity).     

Flood Protection Diversification to Reduce Probabilities of Extreme Losses

Recent catastrophic losses because of floods require developing resilient approaches to flood risk protection. This article assesses how diversification of a system of coastal protections might decrease the probabilities of extreme flood losses. The study compares the performance of portfolios each consisting of four types of flood protection assets in a large region of dike rings. A parametric analysis suggests conditions in which diversifications of the types of included flood protection assets decrease extreme flood losses. Increased return periods of extreme losses are associated with portfolios where the asset types have low correlations of economic risk. The effort highlights the importance of understanding correlations across asset types in planning for large‐scale flood protection. It allows explicit integration of climate change scenarios in developing flood mitigation strategy.     

Poverty and Self‐Control

We argue that poverty can perpetuate itself by undermining the capacity for self‐control. In line with a distinguished psychological literature, we consider modes of self‐control that involve the self‐imposed use of contingent punishments and rewards. We study settings in which consumers with quasi‐hyperbolic preferences confront an otherwise standard intertemporal allocation problem with credit constraints. Our main result demonstrates that low initial assets can limit self‐control, trapping people in poverty, while individuals with high initial assets can accumulate indefinitely. Thus, even temporary policies that initiate accumulation among the poor may be effective. We examine implications concerning the effect of access to credit on saving, the demand for commitment devices, the design of financial accounts to promote accumulation, and the variation of the marginal propensity to consume across income from different sources. We also explore the nature of optimal self‐control, demonstrating that it has a simple and behaviorally plausible structure that is immune to self‐renegotiation.     

信贷资产证券化模式选择与产品设计

信贷资产证券化具有盘活非流动资产、分散本性风险等优势,是公司从资本市场获得低成本融资的主要工具之一。本文假设资产池由多个相关、且均服从算术布朗运动的资产现金流组成,运用公司证券定价理论,得到了基于资产池总现金流的证券化产品价值的解析解。以商业银行为例,研究了资产证券化的动机和最佳发行方式。数值分析表明：资产证券化不仅可以盘活资本,而且可以提高资产的价值;资产池的总价值与进入资产池的各个部分现金流之间的相关系数存在单调递减的关系。最后,针对我国商业银行的资产证券化模式提出了建议。     

OPTIMAL EXCHANGE RATES: A MARKET MICROSTRUCTURE APPROACH

Motivated by the observation that exchange‐rate management resembles market‐making, we use microstructure theory to conduct a welfare analysis of exchange‐rate management, including the “corner solutions” of a free float and a fixed peg. We show that a policy that smoothes out exchange‐rate fluctuations needs to trade off the welfare gain due to lower risk exposure of local producers against the trading losses that the policy would generate due to speculation. We identify the conditions under which exchange‐rate management can increase welfare and argue that these conditions are more likely to be satisfied in illiquid markets, mainly small economies and emerging markets. We also explore the role of a Tobin tax (assuming enforceability) in facilitating exchange‐rate management. (JEL: E58, F31, G14, O24)     

From Welfare to Work: Evaluating a Tax and Benefit Reform Targeted at Single Mothers in Sweden

Abstract. In this paper we evaluate a hypothetical tax and benefit reform to increase the working hours and to decrease welfare participation of single mothers in Sweden. We formulate and estimate simultaneously a structural static model of labor supply and welfare participation. The results suggest that labor supply among single mother households in Sweden is quite elastic, and that there is self‐selection into welfare. We also find that the proposed reform would generate welfare gains for virtually everyone in the sample, benefit low‐income households, and would at the same time generate a small revenue surplus.     

OPTIMAL TAXATION WITH IMPERFECT COMPETITION AND AGGREGATE RETURNS TO SPECIALIZATION

In this article we explore the proposition that, in economies with imperfect competitive markets, the optimal capital income tax is negative and the optimal tax on firms' profits is confiscatory. We show that if the total factor productivity as well as the number of firms or varieties are endogenous instead of fixed, then the optimal fiscal policy can lead to different results. The government faces a trade‐off between the fixed costs that society pays for the introduction of a new firm and the productivity gains associated to the introduction of a new variety. We find that the optimal fiscal policy depends on the relationship between the index of market power, the returns to specialization, and the government's ability to control entry. (JEL: H21, H30, E62)     

Regression Versus Causation,Revisited

I recently discussed pitfalls in attempted causal inference based on reduced‐form regression models. I used as motivation a real‐world example from a paper by Dr. Sneeringer, which interpreted a reduced‐form regression analysis as implying the startling causal conclusion that “doubling of [livestock] production leads to a 7.4% increase in infant mortality.” This conclusion is based on: (A) fitting a reduced‐form regression model to aggregate (e.g., county‐level) data; and (B) (mis)interpreting a regression coefficient in this model as a causal coefficient, without performing any formal statistical tests for potential causation (such as conditional independence, Granger‐Sims, or path analysis tests). Dr. Sneeringer now adds comments that confirm and augment these deficiencies, while advocating methodological errors that, I believe, risk analysts should avoid if they want to reach logically sound, empirically valid, conclusions about cause and effect. She explains that, in addition to (A) and (B) above, she also performed other steps such as (C) manually selecting specific models and variables and (D) assuming (again, without testing) that hand‐picked surrogate variables are valid (e.g., that log‐transformed income is an adequate surrogate for poverty). In her view, these added steps imply that “critiques of A and B are not applicable” to her analysis and that therefore “a causal argument can be made” for “such a strong, robust correlation” as she believes her regression coefficient indicates. However, multiple wrongs do not create a right. Steps (C) and (D) exacerbate the problem of unjustified causal interpretation of regression coefficients, without rendering irrelevant the fact that (A) and (B) do not provide evidence of causality. This reply focuses on whether any statistical techniques can produce the silk purse of a valid causal inference from the sow's ear of a reduced‐form regression analysis of ecological data. We conclude that Dr. Sneeringer's analysis provides no valid indication that air pollution from livestock operations causes any increase in infant mortality rates. More generally, reduced‐form regression modeling of aggregate population data—no matter how it is augmented by fitting multiple models and hand‐selecting variables and transformations—is not adequate for valid causal inference about health effects caused by specific, but unmeasured, exposures.     

基于均值-CVaR模型的企业年金资产配置

基于均值-CVaR模型,根据<企业年金试行办法>中对企业年金基金投资方面的规定,以货币市场工具、中长期国债和金融债、可转债及股票4类投资工具为约束条件,构建了企业年金基金投资的资产配置模型;根据我国金融市场和企业年金基金的具体情况,计算出不同企业年金替代率下,4类投资工具的最优资产配置比例和相应资产配置的风险度量指标--年收益率的CVaR值;并在资产回报率服从正态分布假设下,分析了最优资产配置比例的变化.     

INCOME AND WEALTH CONCENTRATION IN SPAIN FROM A HISTORICAL AND FISCAL PERSPECTIVE

This paper presents series on top shares of income and wealth in Spain using personal income and wealth tax return statistics. Top income shares are highest in the 1930s, fall sharply during the first decade of the Franco dictatorship, then remain stable and low till the 1980s, and have increased since the mid 1990s. The top 0.01% income share in Spain estimated from income tax data is comparable to estimates for the United States and France over the period 1933–1971. Those findings, along with a careful analysis of all published tax statistics, suggest that income tax evasion and avoidance among top income earners in Spain was much less prevalent than previously thought. Wealth concentration has been about stable from 1982 to 2005 as surging real estate prices have benefited the middle class and compensated for a slight increase in financial wealth concentration in the 1990s. We use our wealth series and a simple model to analyze the effects of the wealth tax exemption of stocks for owners‐managers introduced in 1994. We show that the reform induced substantial shifting from the taxable to tax exempt status, hence creating efficiency costs. (JEL D31, H31, O15)