含缺失数据的半参数模型的稳健估计

文章在响应变量随机缺失下,基于分位数回归研究了半参数模型的稳健估计问题。首先基于B样条基函数近似技术,将模型非参数函数的估计问题转化为样条系数向量估计问题;其次,在响应变量随机缺失下,提出了一种新的插补方法,对缺失的响应变量进行多重插补;再次,基于插补后的数据集,构造出新的分位数目标函数,得到模型非参数函数以及参数向量的稳健估计;最后给出了有效算法计算多重插补估计量。通过模拟研究验证了所提方法的有效性和稳健性。     

基于贝叶斯支持向量回归机的稳健参数设计

稳健参数设计是一种质量改进的重要技术，能够从产品生产的源头上减少和控制波动的产生。双响应曲面法是其常用的方法，主要是利用低阶多项式模型来拟合均值和方差响应，但当样本较复杂（如为非线性或者高维样本）时，低阶多项式模型的拟合性能往往较差，求解优化问题效果不佳。支持向量回归机对非线性数据有良好的拟合潜力，但其性能依赖于参数的合理设置，文章将贝叶斯优化应用于支持向量回归机的参数选择，并将优化后的模型应用于稳健参数设计中响应曲面模型的构建，提出一种基于贝叶斯支持向量回归机的稳健参数设计方法。试验结果表明，所提方法和其他常见优化方法相比，可以获得更精确的响应曲面，可以在实际应用中近似得到可靠的最优因子搭配水平。     

基于γ散度的单元水平模型小域稳健估计

在基于抽样调查数据对总体参数进行估计的方法中，小域估计方法能够借助于辅助信息对小样本乃至无样本区域的参数进行有效的估计，并被广泛应用于抽样估计领域。单元水平模型作为小域估计的基本模型之一，是处理单元级别数据估计的有力工具之一。在单元水平模型的应用条件中，需假定区域随机误差和模型随机误差均服从正态分布。然而，在抽样调查中，满足这一条件的调查数据是很少的，尤其是在观测数据中出现离群值时。不满足正态性假设条件下的小域估计量会产生较大的偏差和均方误，因此有必要研究针对正态性假设和离群观测值不敏感的稳健估计方法。通过引入γ散度和γ似然函数，构建了基于单元水平模型的小域稳健估计方法，得到了模型参数的稳健估计和小域目标变量的稳健估计。与现有的稳健估计方法相比，所提新方法能更好地处理区域随机误差和模型随机误差非正态的情形，对于目标变量存在离群观测的情形，具有更好的稳健性，估计均方误更小。在利用模拟数据进行验证中，比较了不同误差分布情形下几类常用估计方法得到的估计量的均方误差，并进一步探究了随着污染分布的方差和比率变化，所得估计量的均方误差变化情形。最后，通过应用于经典的小域估计数据，进一步验证了所提新...     

固定设计异方差非参数回归模型的预测方法

文章针对固定设计下异方差非参数回归模型,考虑了基于多项式样条的三种预测方法,即非外推法、线性外推法和非线性外推法.模拟结果表明非外推预测法的均方根误差(RMSE)和平均绝对误差(MAE)的均值最大,而线性外推法的RMSE和MAE的均值略小于非线性外推法的RMSE和MAE的均值.实证分析结果显示:非外推预测法的平均绝对百分比误差(MAPE)、RMSE和MAE最大,线性外推法的MAPE、RMSE和MAE最小.这表明整体上外推法优于非外推法,而线性外推法是简单可行的.     

基于非参数Bootstrap方法的随机性链梯法及R实现

在我国目前精算实务中,未决赔款准备金评估的不确定性风险逐渐得到重视,对不确定性加以度量显得很有必要。传统链梯法是未决赔款准备金评估最常用的确定性方法,而过度分散泊松模型是与传统链梯法等价的随机性模型,在过度分散泊松模型下,准备金的极大似然估计和传统链梯法的估计值相同。文章把非参数Bootstrap方法应用于过度分散泊松模型中,得到了未决赔款准备金的预测均方误差和预测分布,并通过精算实务中的数值实例应用R软件加以了实证分析。     

一种改进的非参数方法对金融价值风险的估计

文章对利用波动率计算价值风险VaR的方法进行了改进,提出了非参数波动率结合非参数条件核密度条件分位数方法来计算VaR,此非参数方法克服了模型误设的问题,不受波动率模型具体形式的限制,不受新息项分布函数的限制,是一种稳健的适应性方法.同时将此方法应用到中小板综指与创业版指进行实证分析,与相应的半参数及参数方法进行比较,发现文中提出的方法在某种程度上比较稳定可靠.     

非对称损失函数正态分布总体的参数设计

文章在损失为非对称的情况下,讨论了参数设计的可行性,证明了田口方法的稳健设计和灵敏度设计依然有效,给出了参数设计的方法与具体步骤。     

基于不确定性均值-方差模型的稳健静态资产组合选择

文章借助相对熵测度风险资产收益的一阶矩和前两阶矩的不确定性对资产组合终期财富期望效用的影响,基于极大极小化理论建立了模型参数不确定下的稳健静态资产组合模型,运用稳健控制方法获得了模型的最优解;根据最优解,以上证综指1997年1月至2009年6月的月收益数据构建了两个不同区间段的样本做实证研究。结果表明,参数不确定性导致资产组合中风险资产的比例降低,并随着投资者不确定性偏好程度增加降低得越多;历史数据或信息越少,参数不确定性影响越强;均值不确定性的影响强于方差不确定性的影响;即使投资者完全不相信方差的预测功能,但仍在一定程度上相信均值的预测功能。     

熵损失函数下Burr(α)X分布参数的贝叶斯估计

文章研究了Burr(α)X分布参数的各类贝叶斯估计问题.在熵损失函数下分别获得了参数的贝叶斯估计、经验贝叶斯估计、多层贝叶斯估计和E-Bayes估计.证明了参数经验贝叶斯估计的渐近最优性,讨论了参数多层贝叶斯估计和E-Bayes估计的稳健性,通过蒙特卡洛方法对各类估计的MSE进行了数值模拟和比较分析,结果表明:经验贝叶斯估计的均方误差最小,精度较高.     

未决赔款准备金评估的Mack模型及其预测均方误差的实现

目前,在我国精算实务中对未决赔款准备金评估的不确定性风险逐渐重视,对不确定性加以度量显得很有必要。传统链梯法是未决赔款准备金评估最常用的确定性方法,链梯法应用流量三角形评估未来赔款进展模式,将随机性模型和链梯法结合起来就得到随机链梯法。其中,对于非参数随机链梯法已有深入的研究,该方法直接对传统链梯法的假设步骤建立随机模型,而且没有具体的赔款额分布假设。这种度量估计的不确定性,对准备金负债评估的准确性和充足性具有重要的参考价值。文章利用Mack模型得到了未决赔款准备金的预测均方误差,并通过数值例子进行了说明。     

A robust posterior preference multi-response optimization approach in multistage processes

Nowadays, many manufacturing and service systems provide products and services to their customers in several consecutive stages of operations, in each of which one or more quality characteristics of interest are monitored. In these environments, the final quality in the last stage not only depends on the quality of the task performed in that stage but also is dependent on the quality of the products and services in intermediate stages as well as the design parameters in each stage. In this paper, a novel methodology based on the posterior preference approach is proposed to robustly optimize these multistage processes. In this methodology, a multi-response surface optimization problem is solved in order to find preferred solutions among different non dominated solutions (NDSs) according to decision maker's preference. In addition, as the intermediate response variables (quality characteristics) may act as covariates in the next stages, a robust multi-response estimation method is applied to extract the relationships between the outputs and inputs of each stage. NDSs are generated by the ?-constraint method. The robust preferred solutions are selected considering some newly defined conformance criteria. The applicability of the proposed approach is illustrated by a numerical example at the end.     

具有区间灰色特征的多级供应链网络优化设计模型

考虑终端市场需求量和产品单价的区间灰色特征,以及需求的不确定性,研究战略层次上的供应链网络设计及其鲁棒优化问题,当供应链结构的参数发生变动时,供应链整体结构和性能保持鲁棒性。针对传统求解方法的局限性,文章通过引入控制变量,建立了具有灰色特征的供应链网络结构设计模型及其鲁棒优化模型,为验证模型的有效性和可行性,以生鲜农产品为实例分析对象,通过实地调查,运用混合整数非线性规划方法,使用Matlab7.0计算工具,研究了4种不同情景下模型的灵敏度,得出5种不同条件供应链网络的设计结构及整体收益,对比分析得出结论:运用混合整数线性规划方法,能有效解决具有区间灰色特征的供应链网络设计及其鲁棒优化问题;不同条件下供应链网络结构不同,且供应链整体收益值、总成本值和利润值也不相同;只要条件确定,供应链网络结构也是确定的,且该结构对问题的解具有鲁棒特征;控制变量的取值大小反映了决策者的决策特征。     

Analysis of robust design experiments with time-dependent ordinal response characteristics: a quality improvement study from the horticulture industry

An approach to the analysis of time-dependent ordinal quality score data from robust design experiments is developed and applied to an experiment from commercial horticultural research, using concepts of product robustness and longevity that are familiar to analysts in engineering research. A two-stage analysis is used to develop models describing the effects of a number of experimental treatments on the rate of post-sales product quality decline. The first stage uses a polynomial function on a transformed scale to approximate the quality decline for an individual experimental unit using derived coefficients and the second stage uses a joint mean and dispersion model to investigate the effects of the experimental treatments on these derived coefficients. The approach, developed specifically for an application in horticulture, is exemplified with data from a trial testing ornamental plants that are subjected to a range of treatments during production and home-life. The results of the analysis show how a number of control and noise factors affect the rate of post-production quality decline. Although the model is used to analyse quality data from a trial on ornamental plants, the approach developed is expected to be more generally applicable to a wide range of other complex production systems.     

Robust Estimation of Multi-response Surfaces Considering Correlation Structure

Response surfaces express the behavior of responses and can be used for both single and multi-response problems. A common approach to estimate a response surface using experimental results is the ordinary least squares (OLS) method. Since OLS is very sensitive to outliers, some robust approaches have been discussed in the literature. Although there are many methods available in the literature for multiple response optimizations, there are a few studies in model building especially robust models. Assuming correlated responses, in this paper, a robust coefficient estimation method is proposed for multi response problem based on M-estimators. In order to illustrate the performance of the proposed procedure, a contaminated experimental design using a numerical example available in the literature with some modifications is used. Both the classical multivariate least squares method and the proposed robust multivariate approach are used to estimate regression coefficients of multi-response surfaces based on this example. Moreover, a comparison of the proposed robust multi response surface (RMRS) approach with separate robust estimation of single response show that the proposed approach is more efficient.     

Better experimental design by hybridizing binary matching with imbalance optimization

We present a new experimental design procedure that divides a set of experimental units into two groups in order to minimize error in estimating a treatment effect. One concern is the elimination of large covariate imbalance between the two groups before the experiment begins. Another concern is robustness of the design to misspecification in response models. We address both concerns in our proposed design: we first place subjects into pairs using optimal nonbipartite matching, making our estimator robust to complicated nonlinear response models. Our innovation is to keep the matched pairs extant, take differences of the covariate values within each matched pair, and then use the greedy switching heuristic of Krieger et al. (2019) or rerandomization on these differences. This latter step greatly reduces covariate imbalance. Furthermore, our resultant designs are shown to be nearly as random as matching, which is robust to unobserved covariates. When compared to previous designs, our approach exhibits significant improvement in the mean squared error of the treatment effect estimator when the response model is nonlinear and performs at least as well when the response model is linear. Our design procedure can be found as a method in the open source R package available on CRAN called GreedyExperimentalDesign .     

Bayesian two-stage optimal design for mixture models

In this paper, a Bayesian two-stage D–D optimal design for mixture experimental models under model uncertainty is developed. A Bayesian D-optimality criterion is used in the first stage to minimize the determinant of the posterior variances of the parameters. The second stage design is then generated according to an optimalityprocedure that collaborates with the improved model from the first stage data. The results show that a Bayesian two-stage D–D-optimal design for mixture experiments under model uncertainty is more efficient than both the Bayesian one-stage D-optimal design and the non-Bayesian one-stage D-optimal design in most situations. Furthermore, simulations are used to obtain a reasonable ratio of the sample sizes between the two stages.     

Response surface design evaluation and comparison

Designing an experiment to fit a response surface model typically involves selecting among several candidate designs. There are often many competing criteria that could be considered in selecting the design, and practitioners are typically forced to make trade-offs between these objectives when choosing the final design. Traditional alphabetic optimality criteria are often used in evaluating and comparing competing designs. These optimality criteria are single-number summaries for quality properties of the design such as the precision with which the model parameters are estimated or the uncertainty associated with prediction. Other important considerations include the robustness of the design to model misspecification and potential problems arising from spurious or missing data. Several qualitative and quantitative properties of good response surface designs are discussed, and some of their important trade-offs are considered. Graphical methods for evaluating design performance for several important response surface problems are discussed and we show how these techniques can be used to compare competing designs. These graphical methods are generally superior to the simplistic summaries of alphabetic optimality criteria. Several special cases are considered, including robust parameter designs, split-plot designs, mixture experiment designs, and designs for generalized linear models.     

Reliability of global sensitivity indices

Uncertainty and sensitivity analysis is an essential ingredient of model development and applications. For many uncertainty and sensitivity analysis techniques, sensitivity indices are calculated based on a relatively large sample to measure the importance of parameters in their contributions to uncertainties in model outputs. To statistically compare their importance, it is necessary that uncertainty and sensitivity analysis techniques provide standard errors of estimated sensitivity indices. In this paper, a delta method is used to analytically approximate standard errors of estimated sensitivity indices for a popular sensitivity analysis method, the Fourier amplitude sensitivity test (FAST). Standard errors estimated based on the delta method were compared with those estimated based on 20 sample replicates. We found that the delta method can provide a good approximation for the standard errors of both first-order and higher-order sensitivity indices. Finally, based on the standard error approximation, we also proposed a method to determine a minimum sample size to achieve the desired estimation precision for a specified sensitivity index. The standard error estimation method presented in this paper can make the FAST analysis computationally much more efficient for complex models.     

Robust surface estimation in multi-response multistage statistical optimization problems

As the ordinary least squares (OLS) method is very sensitive to outliers as well as to correlated responses, a robust coefficient estimation method is proposed in this paper for multi-response surfaces in multistage processes based on M-estimators. In this approach, experimental designs are used in which the intermediate response variables may act as covariates in the next stages. The performances of both the ordinary multivariate OLS and the proposed robust multi-response surface approach are analyzed and compared through extensive simulation experiments. Sum of the squared errors in estimating the regression coefficients reveals the efficiency of the proposed robust approach.     

Robust 2k factorial design with Weibull error distributions

It is well known that the least squares method is optimal only if the error distributions are normally distributed. However, in practice, non-normal distributions are more prevalent. If the error terms have a non-normal distribution, then the efficiency of least squares estimates and tests is very low. In this paper, we consider the 2^k factorial design when the distribution of error terms are Weibull W(p,σ). From the methodology of modified likelihood, we develop robust and efficient estimators for the parameters in 2^k factorial design. F statistics based on modified maximum likelihood estimators (MMLE) for testing the main effects and interaction are defined. They are shown to have high powers and better robustness properties as compared to the normal theory solutions. A real data set is analysed.