贷款组合信用风险VaR仿真计算的一种优化方法

This paper presents the principle of Monte Carlo optimize calculation of credit risk VaR for loanportfolio using Importance Sampling technique. Based on Matlab language, simulation experiments arecarried out and the result shows this approach can effectively reduce the numher of simulation runs andimprove the precision of parameter estimation.     

比特币市场风险测度的实证研究

文章通过实证分析提出比特币市场价格风险测度体系,从比特币收益率序列的分布、波动性以及是否存在杠杆效应方面着手,在t分布和GED分布假设下,建立Garch(1,1)模型、Egarch(1,1)模型、Tarch(1,1)模型和Parch(1,1)模型,选择合适的模型估算99％和95％置信水平下的比特币风险的VaR值,并采用Kupiec方法对VaR模型进行了返回检验.结果显示,比特币市场价格波动剧烈,具有尖峰后尾特征,不存在杠杆效应,而GED分布的Garch模型是计算比特币市场风险的最合适模型.     

基于VaR方法的市场风险和信用风险的度量

市场风险和信用风险是金融机构所面临的最主要的两类风险。在金融市场迅猛发展的今天,对两类风险的度量和管理成为了金融机构面对的重大挑战之一。VaR模型最初用来度量市场风险,它以严谨的概率统计理论作为依托,将市场风险高度概括为一个数字。之后,VaR方法被引入到信用风险管理中,其中CreditMetrics模型是一个典型例子。文章最后对综合度量市场风险和信用风险进行了初步探讨。     

基于GHSKT分布的WTI原油市场VaR风险度量

众所周知,同正态分布相比而言,金融市场的收益率变量具有偏态和尖峰厚尾特征。文章提出采用GHSKT分布来拟合收益率序列。为了解决参数估计难的问题,提出的强有力EM算法对于解决像包含Bessel函数这样复杂、具有大量局部最优解的优化问题,具有很现实的意义。最后,我们讨论GHSKT分布在WTI原油市场VaR风险度量中的应用。     

中国股市的风险度量研究

本文从沪、深股指收益率的基本统计特征入手,用GARCH-GED模型和核估计模型分别估计了其VaR值,并对模型本身及其估计的VaR进行了较为严格的检验.结论显示GARCHGED模型能够反应股市的短期动态特征,而核估计模型估计的VaR反应了股市风险的长期特征,两个模型相互补充.     

沪深股市的风险测度研究

本文比较风险测度方法在不同置信水平下是否能力有效测度沪深市场风险.针对上证综指收益率具有自相关、波动集聚性和杠杆效应特征,运用ARMA-GJR模型对上证综指的负收益率序列进行MLE以求出条件均值和方差以及标准残差序列,运用10%的数据作为极值数据运用MLE方法来估计广义帕累托分布,还对风险测度方法的估计效果进行分析,认为极值VaR能有效测度沪深股市风险.     

风险价值法VaR对套利风险的衡量研究

在期货套利交易中,投资者最关心的问题,莫过于建仓之后到平仓退出之前这段持有期内如何规避风险。为了从数量上衡量和控制套利交易的风险,文章引入西方现代风险管理方法VaR,对投资者对手中所持有的套利交易资产组合以及单边头寸的风险价值在一段时间内或者每天进行估值和计量,将计算出的风险大小与自身对风险的承受能力加以比较,以此来决定投资额和投资策略,及时调整套利资产组合,减少投资的盲目性,从而达到分散和规避投资风险,尽可能地减少因投资决策失误所带来的损失。     

沪、深股市收益率风险的极值VaR测度研究

资产组合的ＶａＲ是指在某一置信水平下 ,该资产组合可能遭受的最大损失 ,或者说 ,ＶａＲ即资产组合收益率损失分布函数的某一分位点。由于传统的方差 协方差法、历史模拟法、蒙特卡洛模拟法在估计金融资产收益率的ＶａＲ值上的低效 ①,ＦｒａｎｃｏｉｓＬｏｎｇｉｎ等学者便将统计极值理论引入到估测ＶａＲ的研究中来 ② 。本文将运用近年发展起来的这些极值ＶａＲ方法来测度沪、深股市收益率的市场风险 ,同时也对极值方法、半参数方法 ③ 以及传统ＶａＲ方法的测度效果进行比较。　　一、估测ＶａＲ的极值方法通常有两类估测ＶａＲ的极值…     

基于蒙特卡洛方法的金融市场风险VaR的算法分析

为解决蒙特卡洛(Monte Carlo)方法在计算风险价值(Value at Risk,VaR)方面的缺陷,文章首先引入GARCH模型来刻画金融数据的波动聚集性,再引入马尔科夫链蒙特卡洛(Markov Chain Monte Carlo,MCMC)方法,来克服GARCH模型参数估计约束条件带来的估计误差.通过对上证50指数的实证分析表明,引入MCMC方法可以提高模型的估计精确度.     

基于EVT-POT-SV模型的极值风险度量

金融市场常受各种因素的影响造成剧烈波动,资产收益也会因此产生异常变化。针对金融资产收益的厚尾性、波动的异方差性等特征,采用基于Markov链的Monte Carlo模拟积分方法,对随机波动模型进行参数估计并取得标准残差序列,应用极值理论与随机波动模型相结合,建立了基于EVT-POT-SV的动态VaR模型。通过对上证综指收益做实证分析,结果表明：该模型能很好地刻画收益序列的波动性及尾部分布特征,在度量上证综指收益的风险方面更加合理而有效。     

Image‐Based Empirical Importance Sampling: An Efficient Way of Estimating Intensities

Abstract. Very recently, it has been suggested in the biomedical literature to combine computerized image analysis with non‐uniform sampling to increase the efficiency of estimators of intensities of biological cell populations. We give this ingenious idea of empirical importance sampling a stochastic formulation, using point process theory and modern sampling theory. We develop statistical tools for assessing its efficiency and construct optimal model‐based estimators of intensities. Examples of applications of empirical importance sampling in microscopy are provided.     

Adaptive Multiple Importance Sampling

Abstract. The Adaptive Multiple Importance Sampling algorithm is aimed at an optimal recycling of past simulations in an iterated importance sampling (IS) scheme. The difference with earlier adaptive IS implementations like Population Monte Carlo is that the importance weights of all simulated values, past as well as present, are recomputed at each iteration, following the technique of the deterministic multiple mixture estimator of Owen & Zhou (J. Amer. Statist. Assoc., 95, 2000, 135). Although the convergence properties of the algorithm cannot be investigated, we demonstrate through a challenging banana shape target distribution and a population genetics example that the improvement brought by this technique is substantial.     

Improved Sampling-Importance Resampling and Reduced Bias Importance Sampling

Abstract.  The sampling-importance resampling (SIR) algorithm aims at drawing a random sample from a target distribution π. First, a sample is drawn from a proposal distribution q , and then from this a smaller sample is drawn with sample probabilities proportional to the importance ratios π/ q . We propose here a simple adjustment of the sample probabilities and show that this gives faster convergence. The results indicate that our version converges better also for small sample sizes. The SIR algorithms are compared with the Metropolis–Hastings (MH) algorithm with independent proposals. Although MH converges asymptotically faster, the results indicate that our improved SIR version is better than MH for small sample sizes. We also establish a connection between the SIR algorithms and importance sampling with normalized weights. We show that the use of adjusted SIR sample probabilities as importance weights reduces the bias of the importance sampling estimate.     

投资组合动态VaR风险度量

投资组合的VaR风险度量依赖于投资组合中金融资产间联合分布函数的确定,随着投资组合规模的扩大,其VaR的计算难度也不断加大。利用ICA可以将多元联合概率分布函数转化为一元概率分布函数乘积实现简化计算的特点,基于ICA的投资组合动态VaR风险度量方法和计算步骤,克服了多元非正态条件下VaR测算上的困难。实证研究表明,与EWMA模型法、MGARCH模型法相比,ICA法能够准确地度量投资组合动态VaR。     

Importance Sampling for Sums of Lognormal Distributions with Applications to Operational Risk

In this paper we use Importance Sampling to estimate tail probabilities for a finite sum of lognormal distributions. We use a defensive mixture, and develop a method of choosing the parameters via the EM algorithm; we also consider the technique which assumes the importance sampling density to belong to the same parametric family of the random variables to be summed. In both cases, the instrumental density is found by minimizing Cross-Entropy. A comparison based on several simulation experiments shows that the defensive mixture has the best performance. Finally, we study the Poisson-lognormal compound distribution framework and present a real-data application.     

The Gibbs sampler with particle efficient importance sampling for state-space models*

We consider Particle Gibbs (PG) for Bayesian analysis of non-linear non-Gaussian state-space models. As a Monte Carlo (MC) approximation of the Gibbs procedure, PG uses sequential MC (SMC) importance sampling inside the Gibbs to update the latent states. We propose to combine PG with the Particle Efficient Importance Sampling (PEIS). By using SMC sampling densities which are approximately globally fully adapted to the targeted density of the states, PEIS can substantially improve the simulation efficiency of the PG relative to existing PG implementations. The efficiency gains are illustrated in PG applications to a non-linear local-level model and stochastic volatility models.     

A Class of Estimators Using Auxiliary Information in Two-Stage Sampling

This paper presents a general class of estimators for the finite population total when the emphasis is laid on the use of two auxiliary variables in a two-stage sampling.     

A New Sampling Design for Systematic Sampling

A sampling design called “Modified Systematic Sampling (MSS)” is proposed. In this design each unit has an equal probability of selection. Moreover, it works for both situations: N = nk or N ≠ nk. Consequently, the Linear Systematic Sampling (LSS) and Circular Systematic Sampling (CSS) become special cases of the proposed MSS design.     

Sampling the Dirichlet Mixture Model with Slices

We provide a new approach to the sampling of the well known mixture of Dirichlet process model. Recent attention has focused on retention of the random distribution function in the model, but sampling algorithms have then suffered from the countably infinite representation these distributions have. The key to the algorithm detailed in this article, which also keeps the random distribution functions, is the introduction of a latent variable which allows a finite number, which is known, of objects to be sampled within each iteration of a Gibbs sampler.     

More Efficient Approximation of Multiple Integrals using Steady State Ranked Simulated Sampling

This article extends the concept of using the steady state ranked simulated sampling approach (SRSIS) by Al-Saleh and Samawi (2000) for improving Monte Carlo methods for single integration problem to multiple integration problems. We demonstrate that this approach provides unbiased estimators and substantially improves the performance of some Monte Carlo methods for bivariate integral approximations, which can be extended to multiple integrals’ approximations. This results in a significant reduction in costs and time required to attain a certain level of accuracy. In order to compare the performance of our method with the Samawi and Al-Saleh (2007) method, we use the same two illustrations for the bivariate case.