贝塔系数是风险的正确度量吗

在经典的投资组合理论中 ,假设所有资产的报酬率服从对数正态分布 ,因而只需要用收益的方差来度量风险就足够了 ,忽略了偏度的影响。资产收益的分布往往不是对称的 ,偏度是客观存在的 ,而且投资者具有正偏度的爱好。所以必须用方差和偏度来共同度量投资的风险 ,在这种情况下 ,贝塔系数不再是风险的正确度量 ,采用有效的修正方法 ,可以用来对资产进行正确的定价     

The conditional relationship between beta and returns: recent evidence from international stock markets

The risk–return relationship is one of the fundamental concepts in finance that is most important to investors and portfolio managers. Finance theory argues that the beta or systematic risk is the only relevant risk measure for investors. However, many studies have showed that betas and returns are not related empirically, no matter in domestic markets or in international stock markets. This paper examines the conditional relationship between beta and returns in international stock markets for the period from January 1991 to December 2000. After recognizing the fact that while expected returns are always positive, realized returns could be positive or negative, we find a significant positive relationship between beta and returns in up market periods (positive market excess returns) but a significant negative relationship in down market periods (negative market excess returns). The results are robust for both monthly and weekly returns and for two different proxies of the world market portfolio. Our findings indicate that beta is still a useful risk measure for portfolio managers in making optimal investment decisions.     

A BENCHMARK APPROACH TO FINANCE

This paper derives a unified framework for portfolio optimization, derivative pricing, financial modeling, and risk measurement. It is based on the natural assumption that investors prefer more rather than less, in the sense that given two portfolios with the same diffusion coefficient value, the one with the higher drift is preferred. Each such investor is shown to hold an efficient portfolio in the sense of Markowitz with units in the market portfolio and the savings account. The market portfolio of investable wealth is shown to equal a combination of the growth optimal portfolio (GOP) and the savings account. In this setup the capital asset pricing model follows without the use of expected utility functions, Markovianity, or equilibrium assumptions. The expected increase of the discounted value of the GOP is shown to coincide with the expected increase of its discounted underlying value. The discounted GOP has the dynamics of a time transformed squared Bessel process of dimension four. The time transformation is given by the discounted underlying value of the GOP. The squared volatility of the GOP equals the discounted GOP drift, when expressed in units of the discounted GOP. Risk-neutral derivative pricing and actuarial pricing are generalized by the fair pricing concept, which uses the GOP as numeraire and the real-world probability measure as pricing measure. An equivalent risk-neutral martingale measure does not exist under the derived minimal market model.     

基于VaR和两基金分离的投资组合模型

本文使用VaR来度量投资组合的市场风险,构造了一个在可接受期末财富约束条件下,使VaR达到最小的投资组合模型,同时,发现该模型发生了两基金分离现象,因此存在多风险资产情形下的投资组合模型可以退化成为单风险资产情形下的投资组合模型。最后,本文使用简化的单风险模型对我国上海股票市场进行了实证分析,探讨投资者如何在股票和银行借贷中进行最优资产分配。     

Retail investors and financial advisors: New evidence on trust and advice taking heuristics

This paper investigates factors that influence trust and advice taking among retail investors when consulting with financial advisors and making real-world portfolio decisions. The data reveal that non-expert retail investors trust their advisors a lot. Trust formation appears to be well described by a simple heuristic that relies substantially on the advisor's communication style when deciding how much to trust and delegate investment decisions. Portfolio decisions appear to depend more on investors' perceptions about the investor–advisor relationship than on the risk and return characteristics of investments comprising the portfolio choice set. This evidence supports Pentland's (2008) “honest signals” as a more powerful mechanism underlying investor trust than standard metrics based on past performance. Trust and advice-taking heuristics can be interpreted as well adapted to the environment of the non-profit bank cooperatives in which they are observed, implying that trusting based on simple honest signals, although vulnerable to exploitation, can be interpreted as ecologically rational. Features of the investor's environment typical of non-profit cooperative banks imply that the heuristics investors use can perform rather well without requiring investment experience or financial sophistication, which most investors in our sample are well aware they lack.     

Risk management with weighted VaR

This article studies the optimal portfolio selection of expected utility‐maximizing investors who must also manage their market‐risk exposures. The risk is measured by a so‐called weighted value‐at‐risk (WVaR) risk measure, which is a generalization of both value‐at‐risk (VaR) and expected shortfall (ES). The feasibility, well‐posedness, and existence of the optimal solution are examined. We obtain the optimal solution (when it exists) and show how risk measures change asset allocation patterns. In particular, we characterize three classes of risk measures: the first class will lead to models that do not admit an optimal solution, the second class can give rise to endogenous portfolio insurance, and the third class, which includes VaR and ES, two popular regulatory risk measures, will allow economic agents to engage in “regulatory capital arbitrage,” incurring larger losses when losses occur.     

Portfolio Optimization and Martingale Measures

The paper studies connections between risk aversion and martingale measures in a discrete-time incomplete financial market. An investor is considered whose attitude toward risk is specified in terms of the index b of constant proportional risk aversion. Then dynamic portfolios are admissible if the terminal wealth is positive. It is assumed that the return (risk) processes are bounded. Sufficient (and nearly necessary) conditions are given for the existence of an optimal dynamic portfolio which chooses portfolios from the interior of the set of admissible portfolios. This property leads to an equivalent martingale measure defined through the optimal dynamic portfolio and the index 0 < b ≤ 1. Moreover, the option pricing formula of Davis is given by this martingale measure. In the case of b = 1; that is, in the case of the log-utility, the optimal dynamic portfolio defines the numéraire portfolio.     

基于确定性偏好的投资组合选择

文章在对马科维茨证券投资组合模型简要评述的基础上，针对投资者可选标的证券信息集非对称的现实，依据确定性偏好原理，将投资者对可选标的证券信息的确定性程度转换成偏好次序关系，同时结合行为金融学中的前景理论，依确定性偏好次序规则来确定权重函数，并在价值函数-风险的框架下探讨了证券投资组合模型的构建及其最优解，从而在行为金融理论下扩展了马氏证券投资组合模型。实证分析表明，我国证券市场投资者基本是采用线性赋权方式来处理非对称信息集下的投资组合选择的。     

中国股市β系数稳定性研究

β系数是证券或证券组合与市场相互关联的一个概念和参数,它是衡量证券系统风险的重要指标,β系数的稳定性也一直是学术界和投资者特别关注的焦点。本文通过中国股票市场的31个行业数据的研究,得到中国股市样本β值在单位β值(1.00)附近上下波动并呈正态分布;也可以得到组合的β系数还是有较好的稳定性结论。     

Is volatility risk priced in the securities market? Evidence from S&P 500 index options

The authors examine whether volatility risk is a priced risk factor in securities returns. Zero‐beta at‐the‐money straddle returns of the S&P 500 index are used to measure volatility risk. It is demonstrated that volatility risk captures time variation in the stochastic discount factor. The results suggest that straddle returns are important conditioning variables in asset pricing, and investors use straddle returns when forming their expectations about securities returns. One interesting finding is that different classes of firms react differently to volatility risk. For example, small firms and value firms have negative and significant volatility coefficients, whereas big firms and growth firms have positive and significant volatility coefficients during high‐volatility periods, indicating that investors see these latter firms as hedges against volatile states of the economy. Overall, these findings have important implications for portfolio formation, risk management, and hedging strategies. © 2007 Wiley Periodicals, Inc. Jrl Fut Mark 27:617–642, 2007     

The dark side of Bitcoin: Do Emerging Asian Islamic markets help subdue the ethical risk?

Continuous financing of illicit activities (drug and human trafficking, child abuse, cybercrimes) through Bitcoin nurtures the ethical risk of investors. Building on this argument, the current study investigates the extreme tail dependence between Bitcoin and Emerging Asian Islamic (EAI) markets. We report multiple tail-dependent copulas differing across turmoil periods for the whole sample period. Under the ethical-risk hypothesis and modern portfolio theory, our findings demonstrated stronger safe-haven properties of EAIs for Bitcoin to mitigate ethical risk, and higher diversification benefits are documented for both equally adjusted and optimal portfolios. We formulated useful implications for policymakers, governments, regulation authorities, ethical investors, and portfolio managers for policymaking and strategizing their investment portfolios.     

Does corporate governance risk at home affect investment choices abroad?

Disparity between control and ownership rights gives rise to the risk of tunneling by the controlling shareholder, and is prevalent in many emerging market economies and present in some developed countries. At the same time, international investors come from different countries whose home markets are characterized by varying degrees of control–ownership disparity. This paper studies whether this difference in investors' home countries affects their portfolio choice in an emerging market. It combines two unique data sets on ownership and control in business groups, and investor-stock level foreign investment in Korea. A key finding is that investors from low-disparity countries disfavor high-disparity stocks in Korea, but investors from high-disparity countries are indifferent. Moreover, investors from low-disparity countries became averse to disparity only after the Asian financial crisis. These results suggest that the nature of corporate governance in international investors' home countries affects their portfolio choice abroad, and therefore these investors should not be lumped together in the analyses of their portfolio choice.     

Does the More Risk‐Averse Investor hold a Less Risky Portfolio?*

We study the suitability of using absolute risk aversion as a measure of willingness to take risk in the Arrow–Debreu portfolio framework. We define a global measure of risk for the Arrow–Debreu portfolio, which is measured by the sensitivity of an individual's Arrow–Debreu portfolio payoff to the change in the market return. We call this measure ‘conservatism’ and show that the concept of ‘more conservative’ is stronger than that of ‘more risk‐averse.’ A higher absolute risk aversion is only necessary but not sufficient to induce a less risky Arrow–Debreu portfolio. Our results not only challenge the well‐accepted notion that a more risk‐averse investor holds a less risky portfolio, but also suggest a stronger measure – conservatism – for evaluating the riskiness of portfolio.     

基于CVaR的投资组合优化模型研究

风险价值(VaR)是近年来国际金融机构所倡导的测度和控制金融风险的国际主流技术,但是它在投资组合损益服从非正态分布的情形时,不满足一致性风险度量,出现尾部损失测量的非充分性。为了使具有一致性的条件风险值度量(CVaR)克服VaR的不足,构建基于CVaR约束的投资组合优化模型,该模型虑及了投资组合资产的交易成本、交易限制、资金约束和投资者的风险承受度,为制定合理的最优投资组合提供了一种新的思路。     

资本资产定价模型有关假设的逻辑分析

资本资产定价模型 (CAPM)假设投资者具有一致预期 ,关于资本资产各项特征的判断完全相同 ,投资者会选择同一个更优的组合。这样 ,所有投资者最终会同时买入 (或卖出 )某一项资产 ,而不存在相应的卖出 (或买入 )者 ,这说明模型假设存在逻辑上的悖论。市场有效性决定了投资者不可能运用历史数据对当前和将来趋势作出准确判断 ,CAPM模型所提供的最优组合只是对过去不同时期优化值的平均 ,有关假设忽视了投资者对资本资产预期价值判断的多样性。投资者不会统一按照CAPM给出的唯一组合来选择风险资产 ,CAPM的最优投资组合可行集实际上是投资组合可能集合的前沿曲线的渐近线 ,而不是前沿曲线的切线。     

Investment with a Conscience: Examining the Impact of Pro-Social Attitudes and Perceived Financial Performance on Socially Responsible Investment Behavior

This article addresses the growing industry of retail socially responsible investment (SRI) profiled mutual funds. Very few previous studies have examined the final consumer of SRI profiled mutual funds. Therefore, the purpose of this study was to, in an exploratory manner, examine the impact of a number of pro-social, financial performance, and socio-demographic variables on SRI behavior in order to explain why investors choose to invest different proportions of their investment portfolio in SRI profiled funds. An ordinal logistic regression analysis on 528 private investors revealed that two of the three pro-social variables had a positive impact on how much the consumer invested in SRI profiled funds. Moreover, there was proof of a non-altruistic motive for investing in SRI as consumers who perceive that financial return of SRI is equal or better than “regular” mutual funds, invested a greater proportion of their portfolio in SRI profiled mutual funds. Furthermore, the results showed that women and better-educated investors were more likely to invest a greater proportion of their investment portfolio in SRI. Overall, the findings indicate that both financial perceptions and pro-social attitudes are connected to consumer investment in SRI.     

STATIC FUND SEPARATION OF LONG‐TERM INVESTMENTS

This paper proves a class of static fund separation theorems, valid for investors with a long horizon and constant relative risk aversion, and with stochastic investment opportunities. An optimal portfolio decomposes as a constant mix of a few preference‐free funds, which are common to all investors. The weight in each fund is a constant that may depend on an investor's risk aversion, but not on the state variable, which changes over time. Vice versa, the composition of each fund may depend on the state, but not on the risk aversion, since a fund appears in the portfolios of different investors. We prove these results for two classes of models with a single state variable, and several assets with constant correlations with the state. In the linear class, the state is an Ornstein–Uhlenbeck process, risk premia are affine in the state, while volatilities and the interest rate are constant. In the square root class, the state follows a square root diffusion, expected returns and the interest rate are affine in the state, while volatilities are linear in the square root of the state.     

基金投资组合风险评价中VaR的应用研究

近年来我国基金业发展迅猛,其所倡导的价值投资理念获得市场的巨大认同。与此同时,社会上对基金投资风险进行评价的需求日益强烈。如何量化基金投资组合的风险,已成为金融机构及投资者共同关注的问题。利用风险度量的VaR方法,对基金投资股票组合的风险进行实证研究,探讨其在组合风险评价中的应用。     

RISK HORIZON AND REBALANCING HORIZON IN PORTFOLIO RISK MEASUREMENT

This paper analyzes portfolio risk and volatility in the presence of constraints on portfolio rebalancing frequency. This investigation is motivated by the incremental risk charge (IRC) introduced by the Basel Committee on Banking Supervision. In contrast to the standard market risk measure based on a 10‐day value‐at‐risk calculated at 99% confidence, the IRC considers more extreme losses and is measured over a 1‐year horizon. More importantly, whereas 10‐day VaR is ordinarily calculated with a portfolio’s holdings held fixed, the IRC assumes a portfolio is managed dynamically to a target level of risk, with constraints on rebalancing frequency. The IRC uses discrete rebalancing intervals (e.g., monthly or quarterly) as a rough measure of potential illiquidity in underlying assets. We analyze the effect of these rebalancing intervals on the portfolio’s profit and loss distribution over a risk‐measurement horizon. We derive limiting results, as the rebalancing frequency increases, for the difference between discretely and continuously rebalanced portfolios; we use these to approximate the loss distribution for the discretely rebalanced portfolio relative to the continuously rebalanced portfolio. Our analysis leads to explicit measures of the impact of discrete rebalancing under a simple model of asset dynamics.