加权复合分位数回归方法在动态VaR风险度量中的应用

风险价值(VaR)因为简单直观,成为了当今国际上最主流的风险度量方法之一,而基于时间序列自回归(AR)模型来计算无条件风险度量值在实业界有广泛应用。本文基于分位数回归理论对AR模型提出了一个估计方法--加权复合分位数回归(WCQR)估计,该方法可以充分利用多个分位数信息提高参数估计的效率,并且对于不同的分位数回归赋予不同的权重,使得估计更加有效,文中给出了该估计的渐近正态性质。有限样本的数值模拟表明,当残差服从非正态分布时,WCQR估计的的统计性质接近于极大似然估计,而该估计是不需要知道残差分布的,因此,所提出的WCQR估计更加具有竞争力。此方法在预测资产收益的VaR动态风险时有较好的应用,我们将所提出的理论分析了我国九只封闭式基金,实证分析发现,结合WCQR方法求得的VaR风险与用非参数方法求得的VaR风险非常接近,而结合WCQR方法可以计算动态的VaR风险值和预测资产收益的VaR风险值。     

大数据下分位数回归通讯有效算法及其应用

考虑风险度量中常见的分位数回归模型，给出在超大容量数据且复杂数据类型下的几类快速分布式算法.虽然仅考虑分位数回归模型，但本文提供的算法大多数可以应用到其它更一般的模型中.由于分位数回归模型的目标函数为非光滑函数，通常的分块集成法和光滑函数高效通讯算法并不适用.本文首先针对完整观测数据，给出了分位数回归模型参数估计的等度连续法，光滑函数逼近法和改进的数萃(Meta)方法三种分布式通讯有效算法.进一步，考虑了非平衡半监督数据，分别针对无标签数据样本量较小和较大两种情形，提出了加权损失函数法和改进的数萃方法两种数据融合方法.所提出的方法可以把分散在不同机器上的半监督数据进行数据融合，从而实现不同数据类型和不同样本量情形下的高效通讯分布式计算，提高算法的精度和参数估计的效率.本文通过大量仿真模拟研究了所提出的算法在有限样本下的表现，并将其应用到了洛杉矶流浪人口数的实际数据分析中，发现其均具有较好的准确性.     

石油期货收益率的分位数建模及其影响因素分析

石油期货收益率的分位数反映了收益率分布特征和石油市场风险特征,有必要建模考察分位数的变化模式与影响因素。针对现有研究在模型方法和分析角度上的不足,本文考虑分位数受市场冲击影响而产生的非线性自回归特征,提出门限CAViaR模型并用以分析石油期货收益率的分位数及其影响因素。基于1998-2009年布伦特原油期货价格的研究表明,石油期货收益率的分位数具有自回归特征并受前期油价涨跌的不对称影响,且油价下跌的作用更强。左尾分位数受油价涨跌的共同影响,而右尾分位数仅受油价下跌的影响,二者呈现不同特征。此外,本文通过考察分位数的动态变化模式揭示了油价风险特征,具有重要的风险管理作用。     

基于改进均值回归的波罗的海原油运价指数模型研究

针对波罗的海原油运价指数波动机理,通过分析原油运价指数的均值回归特性,研究其波动趋势,运用单位根检验及方差比检验方法对原油运价指数的均值回归特性进行验证,从而对传统均值回归模型进行改进,给出参数的估计方式,对波罗的海原油运价指数进行分析预测并验证改进模型的拟合效果及预测精度。本文的特色与创新一是基于特性检验,建立"均值水平"随时间变动的均值回归方程,体现原油运价指数均值随时间变化的特征;二是基于柯尔莫哥洛夫前向方程得到基于改进均值回归模型的预测模型,确定预测值及置信区间,从而对原油运价指数样本路径进行拟合,并通过与传统预测模型的比较,表明改进预测模型的显著性。实证结果表明,原油运价指数具有显著的均值回归的特性,且改进后的均值回归方法平均预测相对误差达到0.1597,低于传统模型的平均预测相对误差0.1908。     

基于LASSO分位数回归的对冲基金投资策略研究

由于对冲基金采用了灵活的投资技巧,其收益序列往往表现出与传统投资方式不同的统计特征与风险收益能力,已有方法难以有效地评价其投资绩效.基于LASSO分位数回归,从影响对冲基金收益的众多风险因子中,挑选出重要的风险因子,考察在不同分位点处对冲基金的收益与风险之间关系,识别对冲基金投资风格,继而给出对冲基金投资绩效评价方法.为验证基于LASSO分位数回归的投资风格识别与投资绩效评价效果,构建对冲基金风格组合投资方案,并将其与基于均值回归构建的组合投资、等权组合投资、Markowitz组合投资等经典的组合投资决策方法进行比较.实证研究结果表明,基于LASSO分位数回归的投资绩效评价方法最为有效,给出的组合投资方案能够获得较高的风险调整收益.     

基于PLS的变权重组合预测方法

在目前研究较多的组合预测模型中加权系数是不变的.事实上,假定加权系数为常数,组合预测模型并不能很好地反映预测方法的有效性.基于以上事实,本文提出基于PLS的变权重组合预测方法,利用偏最小二乘回归方法求得组合预测的权重函数.最后通过实例分析验证了方法的有效性.     

基于变系数分位点回归的金砖四国金融稳定分析

金融不稳定性累积到一定程度就会引发金融危机,而新兴市场作为世界经济发展的重要增长点,同时也是金融危机爆发的重灾区.因此,新兴市场金融稳定性的研究至关重要.本文基于新兴市场代表国家——金砖四国(中国,俄罗斯,印度,巴西)的主要综合股指对金融稳定性进行了实证研究.与传统金融稳定性的研究方法不同,本文考虑系统性冲击在正常和极端市场下对不同国家金融市场的影响.首先应用分位数回归模型对金砖四国的金融稳定性进行检验,进而基于变系数分位数模型研究系统性冲击对金融市场稳定性的影响随时间变化的趋势,对金融稳定性进行了时变分析.实证结果表明,金砖四国都具有某种程度的金融不稳定性,近期中国和巴西在5%分位点处的金融不稳定性受系统性冲击的影响相对于印度和俄罗斯更加剧烈.     

基于非线性分位数回归模型的多期VaR风险测度

多期VaR主要受到持有期及波动率两个变量的影响,并且其影响模式(线性或非线性)的确定对于准确地进行VaR风险测度至关重要。非线性分位数回归模型,能够克服线性分位数回归模型只能揭示多期VaR及其影响因素之间线性依赖关系的局限,从而提高多期VaR风险测度的准确性。结合波动模型与两个非线性分位数回归方法:QRNN和SVQR,给出了多期VaR风险测度的三类方案:波动模型法、QRNN+波动模型法、SVQR+波动模型法。选取3个股票价格指数作为研究对象,考虑了6种不同形式的波动模型,得到了18个多期VaR风险测度方法进行实证比较,结果表明:波动模型选择影响到多期VaR风险测度效果;SVQR+波动模型法略优于QRNN+波动模型法,并且两者显著优于波动模型法。     

比例数据基于Tobit分位数回归模型的贝叶斯变量选择

针对家庭商业健康保险参保比例在[0,1]闭区间上取值的特点,本文基于Tobit模型给出了比例响应数据的贝叶斯分位数回归建模方法。通过引入回归系数的“Spike-and-slab”先验分布,应用EM算法我们提出了基于门限规则的贝叶斯变量选择方法。大量数值模拟研究验证了所提的贝叶斯变量选择方法的有效性,且具有易操作、计算量小等优点。最后,将此方法应用到家庭商业健康保险数据的实证分析,研究不同分位数水平下家庭健康保险参保比例的影响因素,得到了许多有意义的研究结果。     

基于时变稳健加权最小二乘法的股市收益率预测

提出一类时变参数稳健加权最小二乘法(TRWLS),并将其用于预测标准普尔500指数收益率.该方法将时间相关权重与稳健估计权重相结合,既能捕捉参数时变性,又能降低数据噪声的影响.TRWLS模型组合揭示了经济和统计意义上均显著的收益率可预测性,而且预测能力明显高于普通最小二乘法.TRWLS模型的预测表现也好于传统时变参数模型和稳健回归模型.其预测能力主要来源于时间权重和稳健性权重的互补性以及超参数的学习能力.预测结果在调整多元信息组合方法、权重核函数和验证集长度的情况下均具有稳健性.     

Criteria for selecting a production control philosophy

Logistic objectives constitute a compromise between having short leadtimes and a low volume of work in progress on the one hand and a high resource loading and due date obligation on the other. Miscellaneous production planning approaches offered today provide different combinations of logistic objectives for satisfying a manufacturing strategy. To combine the strength of the various approaches into a unified system, a new approach based on a dynamic and distributed production planning methodology is proposed. To customize the approach, various analyses and specifications have to be made and for that reason some important characteristics and criteria for analysing production control philosophies will be given.     

The social construction of the meaning of acute stressors: a qualitative study of the personal accounts of police officers using a stress counselling service

The police profession is one in which acute stressors are encountered more frequently than in other occupations. Using the personal accounts of 35 police officers attending an in-house stress counselling clinic, the aim of the present study was to provide a qualitative examination of how the institutional context of policing influenced the ways in which acute stressors signified to individual police officers experiencing felt distress. Using the framework of Rational Emotive Behaviour Therapy as an analytical tool, it is argued that beliefs contributing to the experience of felt distress are related to the way in which policing as both an identity and an activity is constructed through the police organizational culture. Not only do these constructions influence the ways in which officers perceive themselves and their environments, but they also operate at the collective level to 'normalize' some emotional responses and to 'pathologize' others which, it is argued, could impact upon the outcomes of interventions such as stress counselling.     

The moderating role of social support in Karasek's job strain model

This paper examines whether social support is a boundary-determining criterion in the job strain model of Karasek (1979). The particular focus is the extent to which different sources of social support, work overload and task control influence job satisfaction, depersonalization and supervisor assessments of work performance. Hypotheses are tested using prospective survey data from 80 clerical staff in a university setting. Results revealed 3-way interactions among levels of support (supervisor, co-worker, non-work), perceived task control and work overload on levels of work performance and employee adjustment (self-report). After controlling for levels of negative affect in all analyses, there was evidence that high levels of supervisor support mitigated against the negative effects of high strain jobs on levels of job satisfaction and reduced reported levels of depersonalization. Moreover, high levels of non-work support and co-worker support also mitigated against the negative effects of high strain jobs on levels of work performance. The results are discussed in terms of the importance of social support networks both at, and beyond, the work context.     

Job insecurity, coping resources and personality dispositions in occupational strain

This paper presents research on the relationships between the work-related stressor of perceived job insecurity and various indicators of occupational strain, taking into account employees' personality dispositions (trait negative and positive affectivity) and coping resources. Respondents were 222 Australian public servants surveyed during organizational restructuring that involved downsizing and threat to job certainty. The research was formulated within an adaptation of Osipow, Doty, and Spokane's (1985) framework of stress-strain-coping that included the possible direct as well as moderating effects of personality dispositions in reporting occupational strain (Parkes, 1990). Findings from hierarchical regression analyses indicate consistent significant independent effects of personality dispositions, coping resources and perceived job insecurity on various indicators of strain. There was also support for the moderating roles of negative affectivity and self-care in the relation between perceived job insecurity and physical strain. Implications for the role of dispositional factors, especially negative affectivity, and the utility of various coping resources in accounting for occupational strain in times of threatened job security are discussed.     

Introduction to Special Section on Sensitivity Analysis and Summary of NCSU/USDA Workshop on Sensitivity Analysis

This guest editorial is a summary of the NCSU/USDA Workshop on Sensitivity Analysis held June 11–12, 2001 at North Carolina State University and sponsored by the U.S. Department of Agriculture's Office of Risk Assessment and Cost Benefit Analysis. The objective of the workshop was to learn across disciplines in identifying, evaluating, and recommending sensitivity analysis methods and practices for application to food‐safety process risk models. The workshop included presentations regarding the Hazard Assessment and Critical Control Points (HACCP) framework used in food‐safety risk assessment, a survey of sensitivity analysis methods, invited white papers on sensitivity analysis, and invited case studies regarding risk assessment of microbial pathogens in food. Based on the sharing of interdisciplinary information represented by the presentations, the workshop participants, divided into breakout sessions, responded to three trigger questions: What are the key criteria for sensitivity analysis methods applied to food‐safety risk assessment? What sensitivity analysis methods are most promising for application to food safety and risk assessment? and What are the key needs for implementation and demonstration of such methods? The workshop produced agreement regarding key criteria for sensitivity analysis methods and the need to use two or more methods to try to obtain robust insights. Recommendations were made regarding a guideline document to assist practitioners in selecting, applying, interpreting, and reporting the results of sensitivity analysis.     

Job stress, job strain, and psychological withdrawal among Dutch university staff: towards a dualprocess model for the effects of occupational stress

This study examined the antecedents of job strain (emotional exhaustion, health complaints) and withdrawal behaviour (e.g. lowered organizational commitment) among a cross-sectional sample of 131 academic staff members of the law department of a large Dutch university. Conservation of resources theory (Hobfoll, 1989) provided the theoretical background for this study. Strains and withdrawal behaviours were expected to be most prominent among those who reported having few resources and/or who reported high job demands. Structural equation modelling revealed that this was indeed the case. As predicted, differential patterns of effects emerged for job demands and job resources. Analysis of the effects of four job-specific stressors revealed that especially the structural aspects of a staff member's teaching task (e.g. the number of students in their classes) contributed strongly to perceived job demands. Theoretical and practical implications of the study are discussed.     

Distinguishing traumatic, vicarious and routine operational stressor exposure and attendant adverse consequences in a sample of police officers

Problems in studying occupational stress within the police service are identified and the paucity of work on operational duties as potential stressors are discussed. The present study reports the results of a factor analysis of operational stressors (N = 601 serving British police officers) that revealed three factors: exposure to death and disaster; violence and injury; sexual crime. These were demonstrated to be reliable scales and were included in logistic regression models together with a range of demographic and psychological variables. Models were applied to men and women separately, which showed there to be different predictors of the likelihood of suffering distress (measured by the General Health Questionnaire, GHQ) in terms of the officer's gender and operational role. Overall the model for women officers was better at predicting psychological distress than that for men. These findings are related to aspects of the police occupational culture. Further discussion is offered that conceptualizes police operational stressors as traumatic, routine and vicarious. Finally, some implications are drawn for the provision of stress intervention in the light of this differentiation.     

Dermal Uptake of 18 Dilute Aqueous Chemicals: In Vivo Disappearance‐Method Measures Greatly Exceed In Vitro‐Based Predictions

Average rates of total dermal uptake (K_up) from short‐term (e.g., bathing) contact with dilute aqueous organic chemicals (DAOCs) are typically estimated from steady‐state in vitro diffusion‐cell measures of chemical permeability (K_p) through skin into receptor solution. Widely used (“PCR‐vitro”) methods estimate K_up by applying diffusion theory to increase K_p predictions made by a physico‐chemical regression (PCR) model that was fit to a large set of K_p measures. Here, K_up predictions for 18 DAOCs made by three PCR‐vitro models (EPA, NIOSH, and MH) were compared to previous in vivo measures obtained by methods unlikely to underestimate K_up. A new PCR model fit to all 18 measures is accurate to within approximately threefold (r = 0.91, p < 10^?5), but the PCR‐vitro predictions (r > 0.63) all tend to underestimate the K_up measures by mean factors (UF, and p value for testing UF = 1) of 10 (EPA, p < 10^?6), 11 (NIOSH, p < 10^?8), and 6.2 (MH, p = 0.018). For all three PCR‐vitro models, log(UF) correlates negatively with molecular weight (r² = 0.31 to 0.84, p = 0.017 to < 10^?6) but not with log(vapor pressure) as an additional predictor (p > 0.05), so vapor pressure appears not to explain the significant in vivo/PCR‐vitro discrepancy. Until this discrepancy is explained, careful in vivo measures of K_up should be obtained for more chemicals, the expanded in vivo database should be compared to in vitro‐based predictions, and in vivo data should be considered in assessing aqueous dermal exposure and its uncertainty.     

Systems Resilience for Multihazard Environments: Definition,Metrics, and Valuation for Decision Making

The United Nations Office for Disaster Risk Reduction reported that the 2011 natural disasters, including the earthquake and tsunami that struck Japan, resulted in $366 billion in direct damages and 29,782 fatalities worldwide. Storms and floods accounted for up to 70% of the 302 natural disasters worldwide in 2011, with earthquakes producing the greatest number of fatalities. Average annual losses in the United States amount to about $55 billion. Enhancing community and system resilience could lead to massive savings through risk reduction and expeditious recovery. The rational management of such reduction and recovery is facilitated by an appropriate definition of resilience and associated metrics. In this article, a resilience definition is provided that meets a set of requirements with clear relationships to the metrics of the relevant abstract notions of reliability and risk. Those metrics also meet logically consistent requirements drawn from measure theory, and provide a sound basis for the development of effective decision‐making tools for multihazard environments. Improving the resiliency of a system to meet target levels requires the examination of system enhancement alternatives in economic terms, within a decision‐making framework. Relevant decision analysis methods would typically require the examination of resilience based on its valuation by society at large. The article provides methods for valuation and benefit‐cost analysis based on concepts from risk analysis and management.     

UNIX系统性能监控简述及shell系统资源统计程序

本文简要阐述了unix系统中(主要以IBM的AIX为例)进行系统性能管理的几种命令行工具,并通过编写shell实例程序,运用其中提到的工具实现系统资源利用率的统计程序,为做好unix系统管理和调优提供参考.