高维纵向数据中边际模型和混合效应模型的若干研究
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摘要
这篇论文致力于对高维纵向数据领域中边际模型和混合效应模型的深入研究以及方法上的延伸。
     纵向数据是指对同一个个体或者试验单位在不同时间进行观测而得到的由截面和时间序列相融合的数据。它在心理学、社会学、医学以及生物学等科学领域中经常出现,其最大的特点是其将截面数据和时间序列数据结合在一起,既能分析出观测单元随时间变化的趋势,又能分析出总体的变化趋势。近年来,对纵向数据各种模型的研究引起了国内外统计学家的广泛关注。在本文中,我们主要研究了两类模型:边际模型和混合效应模型,探讨了它们在高维情况下的参数估计和变量选择的问题。
     在本文的第二章,对于特殊的广义线性模型Logistic回归模型,我们提出了一种两阶段的收缩估计方法来同时进行变量选择和参数估计,其主要思路是在广义估计方程的非保守向量场内,通过引入一种特殊的加权机制来构造加权最小二乘型的函数,然后利用Zou[104]所提出的自适应性最小绝对缩减和变量选择算子得到回归系数的稀疏估计。我们在维数发散情况下,证明了该收缩估计方法具有Oracle性质,即模型选择过程的相合性和非零参数估计的渐进正态性。同时,我们对参数估计的协方差函数提出了一种相合的三明治估计,并且提出了相合的惩罚二次型准则来应对调整参数的选取。最后,我们讨论了一般广义线性模型下该收缩方法的应用。
     随着计算机计算技术和其他现代技术的发展,使得收集和处理海量复杂数据己成为可能,比如利用DNA微阵列技术收集到的基因表达数据。但是,在纵向数据情况下,超高维基因数据的特征选择一直没有得到很好的解决,因此,为了填补这一空白,在本文第三章中我们提出了一种基于广义估计方程的筛选准则,它只须对一二阶矩和工作相关系数矩阵进行假定。不同于文献中已有的筛选方法,该方法无须拟合所有的边际模型或计算配对相关性,它只须通过对估计函数计算一次即可快速完成特征的选择。同时我们还证明了该方法具有稳健性,即使在工作相关系数矩阵错误假定下,仍然具有Sure Screening性质。
     本文的第四章是通过对关于癫痫发作次数的某实际数据的观察,提出了广义单指标模型来对数据建模。为了让拟合的广义单指标模型具有可识别性,我们首先采用了“消去一个分量”的方法对指标向量重参数化。然后,我们提出了基于广义估计方程的核估计方法和截面方法对广义单指标模型中的未知连接函数和指标向量的方向进行估计。我们证明了指标向量的(?)相合性,并且给出了广义单指标函数的渐进性质。另外,我们提出了拟费歇尔得分算法对连接函数和指标向量的方向进行迭代估计。
     在本文的第五章,我们提出了一种基于分层似然的双惩罚方法,实现了对广义线性混合效应模型的固定效应和随机效应同时进行选择的目的。该方法不仅避免了高维积分来得到用于效应选择的目标函数,而且通过Cholesky分解保证了所选随机效应对应的协方差矩阵的正定性。我们证明了该方法在不需要损失函数的凸型条件下具有Oracle性质。而且,我们提出了一种两阶段算法来有效地实现这个方法,并提出了基于分层似然的贝叶斯信息准则用于对调整参数进行自动赋值。
     通过大量的模拟实验我们比较了本文中提出的各方法和一些已有的方法,因而验证了这些新方法的有效性。另外,我们还将这些方法用于分析各种实际数据,比如交叉试验数据,抗癌抑制剂CCI-779的二期临床试验数据,癫痫发作次数数据以及多中心爱滋病群组研究的数据,说明了这些方法的应用价值所在。
This dissertation is devoted to methodology development for marginal models and mixed effects models in the literature of high-dimensional longitudinal data analysis.
     Longitudinal data typically refers to the data containing cross-sectional and time series observations at different time points for a number of individuals. It arises frequently from psychological studies, social sciences, medical studies and biological sciences. Its major character is to put cross-sectional data and time series data together, so that it is able to not only analyse the trend of individuals, but also analyse the total change trend. Recently, many statisticians pay attention to various models of longitudinal data. And in this dissertation, we focus on two types of models:marginal models and mixed effects models. We discuss parameter estimation and variable selection under these two types of models in the high-dimensional longitudinal data analysis.
     In Chapter2, for the logistic regression model, which is a special generalized linear model, we propose a two-stage shrinkage approach for simultaneous variable selection and parameter estimation. Its main idea is first to construct a weighted least-squares type function using a special weighting scheme on the non-conservative vector field of the generalized estimating equations model, and then to produce sparse estimation of the regression coefficients in the sprit of the adaptive Least Absolute Shrinkage and Selection Operator (Zou,2006). The proposed procedure enjoys the oracle properties in high-dimensional framework where the number of parameters grows to infinity with the number of clusters, i.e., with probability tending to1, we select the subset consisting of all the indices of nonzero coefficients and the estimators of the nonzero coefficients have the asymptotic normality property. Moreover, we prove the consistency of the sandwich formula of the covariance matrix even when the working correlation matrix is misspecified and develop a consistent penalized quadratic form function criterion for the selection of tuning parameter. Finally, we extend the technique to the general marginal longitudinal generalized linear models.
     With rapid development of computing power and other modern technology, high-throughput data sets of unprecedented size and complexity are often encountered in many statistical studies, such as gene expression data from DNA microarray experiments. How-ever, there are virtually no solutions for feature screening in the ultra-high dimensional longitudinal gene expression data setting. To fill in this gap. we propose a novel GEE- based screening procedure in Chapter3, which only pertains to the specifications of the first two marginal moments and a working correlation strueture. Different from exist-ing screening methods, the new method merely involves making a single evaluation of estimating functions instead of fitting all separate marginal models or computing each pairwise correlation. And we show that the proposed method is robust with respect to the mis-specification of correlation structures and enjoys the sure screening property.
     Motivated by an analysis of a real longitudinal data set from an epileptic seizure study, we suggest a marginal generalized single-index model in Chapter4. To well i-dentify the index in estimation, we first use the "remove-one-component" method for re-parametrization. Then, we suggest using a kernel GEE-type method to estimate the unknown link function and using a profile-type method to estimate the unknown index. We prove the estimator of the index is root-n consistent, and establish the asymptotic property of the nonparametric estimator of the generalized single-index function. A quasi-Fisher scoring type algorithm is also developed to estimate the unknown link function and the index iteratively.
     In Chapter5, we develop a double penalized hierarchical likelihood for selecting fixed and random effects in generalized linear mixed models simultaneously. The proposed method not only avoids the calculation of high-dimensional integral to define an objective function for effect selection, but also guarantee the positive defmiteness of the covariance matrix of selected random effects through Cholesky decomposition. We show that the resulting estimator enjoys the oracle properties with no requirement on the convexity of loss function. Moreover, a two-stage algorithm is proposed to effectively implement this approach. And an H-likelihood-based Bayesian information criterion is developed for tuning parameter selection.
     Moreover, we compare each proposal in this dissertation with its related alternatives by comprehensive simulation studies to illustrate the efficieney of our proposals. We also demonstrate the use of our proposals through a wide range of applications in real data analysis, such as the data from a crossover trial, a phase Ⅱ study of the anti-cancer inhibitor CCI-779, an epileptic seizure study, and a multi-center AIDS cohort study.
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