一类非线性差分不等式中未知函数的估计及其应用

该文建立了一类非线性差分不等式.此不等式包含了非线性函数与未知函数的复合函数,是一个具有多重和的差分不等式.利用单调技巧、放大方法、积分中值定理、变量替换技巧、差分和求和技巧,给出了未知函数的上界估计.最后,用所得结果研究了差分方程解的估计.     

协变量区间删失时线性模型的参数估计

本文研究了当协变量为区间数据时的线性模型，通过构造区间数据变量的条件均值，得到了回归参数的估计，当协变量的分布已知时，证明了估计的无偏性与强相合性．时协变量的分布未知的情形也作了讨论．文中还作了若干模拟计算，从模拟的结果不难发现，利用本文提出的方法所获得的估计简便且具有较高的精度．     

一个新的非线性差分不等式及其应用

建立了一个一般形式的二变量的差分不等式,该不等式和号内包含两个不同的没有假设单调性的未知函数的复合函数.使用了单调化技术,利用了强单调的性质,给出了未知函数的估计.结果能对Ma Q H 等人文中考虑的离散不等式的未知函数进行估计.进一步,给出了差分方程解的估计.     

多类型复发事件下变系数加性乘积比率回归模型

本文基于多类型复发事件数据,讨论了一个新的加性乘积比率回归模型,该模型包括两部分,其中第一部分为可加Aalen模型,其中协变量影响为加性的且与时间有关.第二部分为Cox回归模型,其中协变量有乘性影响.利用估计方程的方法,给出了该模型中未知参数和非参数函数的一种估计方法,并利用现代经验过程理沦证明了所得估计的相合性和渐近正态性.     

一个推广的二变量时滞积分不等式及其应用

建立了一类二变量的时滞积分不等式,不等式包含一个一重积分和两个二重积分,二重积分内包含两个不同的没有假设单调性的未知函数的复合函数.使用单调化技术,给出积分不等式中未知函数的估计.结果能对相关文献中考虑的积分不等式中未知函数进行估计.进一步,结果给出了一类积分-微分方程解的估计.     

部分线性模型参数极大似然估计的收敛速度

针对部分线性模型, 在其随机误差的分布函数属于刻度族, 刻度参数未知, 并且响应变量的观测值为区间删失数据的情形下, 讨论了其Sieve极大似然估计的强相合性和弱收敛速度.     

缺失数据下非线性半参数EV模型的估计

考虑解释变量带有测量误差且响应变量随机缺失情形下的非线性半参数EV模型. 利用核实数据,构造了未知参数和非参数函数的两种估计.证明了未知参数估计的渐近正态性,给出了非参数函数估计的最优收敛速度.     

单调函数型数据半参数模型的估计（英文）

本文研究了单调约束条件下函数型数据半参数模型的估计问题,利用非线性混合效应模型的方法,给出模型中未知参数向量和单调参数曲线的估计,并通过模拟对提出的方法进行数值分析.     

一类差分不等式及其应用

建立一类二变量的和差分不等式,该不等式包含了一个一重和与两个二重和,二重和号内包含两个不同的没有假设单调性的未知函数的复合函数.使用单调化技术,利用了强单调的性质,给出了差分不等式中未知函数的估计.结果能使我们对相关文献中考虑的差分不等式中未知函数进行估计.进一步,用结果给出了一类差分方程解的估计.     

相依数据下一般函数核估计的强一致收敛速度

在很多统计回归模型中,都涉及到对未知均值函数或者对某已知函数的未知条件数学期望的估计.本文针对这一问题,给出在数据是α-混合相依时一般函数的条件数学期望的核估计,并讨论它的强一致收敛速度.     

Estimation and test of restricted linear EV model with nonignorable missing covariates

This paper deals with estimation and test procedures for restricted linear errors-invariables (EV) models with nonignorable missing covariates. We develop a restricted weighted corrected least squares (WCLS) estimator based on the propensity score, which is fitted by an exponentially tilted likelihood method. The limiting distributions of the proposed estimators are discussed when tilted parameter is known or unknown. To test the validity of the constraints, we construct two test procedures based on corrected residual sum of squares and empirical likelihood method and derive their asymptotic properties. Numerical studies are conducted to examine the finite sample performance of our proposed methods.     

Robust estimation for partially linear models with large-dimensional covariates

We are concerned with robust estimation procedures to estimate the parameters in partially linear models with large-dimensional covariates. To enhance the interpretability, we suggest implementing a nonconcave regularization method in the robust estimation procedure to select important covariates from the linear component. We establish the consistency for both the linear and the nonlinear components when the covariate dimension diverges at the rate of o(n1/2), where n is the sample size. We show that the robust estimate of linear component performs asymptotically as well as its oracle counterpart which assumes the baseline function and the unimportant covariates were known a priori. With a consistent estimator of the linear component, we estimate the nonparametric component by a robust local linear regression. It is proved that the robust estimate of nonlinear component performs asymptotically as well as if the linear component were known in advance.Comprehensive simulation studies are carried out and an application is presented to examine the fnite-sample performance of the proposed procedures.     

Estimation and test procedures for composite quantile regression with covariates missing at random

In this paper, we study the weighted composite quantile regression (WCQR) for general linear model with missing covariates. We propose the WCQR estimation and bootstrap test procedures for unknown parameters. Simulation studies and a real data analysis are conducted to examine the finite performance of our proposed methods.     

Prognostic of glial tumours

We deal with the problem of finding a suitable model to predict survival of patients suffering from glial tumours as a function of several covariates. Estimation is based upon a retrospective study on 192 patients. Data were collected in the Hospital of Bordeaux and are analysed by Commenges and Dartigues¹ using a Cox model. In the present paper we use dynamic Bayesian models which allow effects of the covariates to change with time through a stochastic structure. The survival function at one year is also calculated as a function of the covariates with the highest prognostic values and two factors (linear combinations of the covariates) are identified which synthesize information related to the general state of the patient (age, first symptom, etc.) and the characteristics of the tumour (diameter, localization, etc.), respectively. Survival at one year is then calculated as function of the two factors. Results are reported in tabular and graphic forms.     

A general transformation class of semiparametric cure rate frailty models

We consider a class of cure rate frailty models for multivariate failure time data with a survival fraction. This class is formulated through a transformation on the unknown population survival function. It incorporates random effects to account for the underlying correlation, and includes the mixture cure model and the proportional hazards cure model as two special cases. We develop efficient likelihood-based estimation and inference procedures. We show that the nonparametric maximum likelihood estimators for the parameters of these models are consistent and asymptotically normal, and that the limiting variances achieve the semiparametric efficiency bounds. Simulation studies demonstrate that the proposed methods perform well in finite samples. We provide an application of the proposed methods to the data of the age at onset of alcohol dependence, from the Collaborative Study on the Genetics of Alcoholism.     

Generalized partially linear models with missing covariates

In this article we study a semiparametric generalized partially linear model when the covariates are missing at random. We propose combining local linear regression with the local quasilikelihood technique and weighted estimating equation to estimate the parameters and nonparameters when the missing probability is known or unknown. We establish normality of the estimators of the parameter and asymptotic expansion for the estimators of the nonparametric part. We apply the proposed models and methods to a study of the relation between virologic and immunologic responses in AIDS clinical trials, in which virologic response is classified into binary variables. We also give simulation results to illustrate our approach.     

Partial linear single index models with distortion measurement errors

We study partial linear single index models when the response and the covariates in the parametric part are measured with errors and distorted by unknown functions of commonly observable confounding variables, and propose a semiparametric covariate-adjusted estimation procedure. We apply the minimum average variance estimation method to estimate the parameters of interest. This is different from all existing covariate-adjusted methods in the literature. Asymptotic properties of the proposed estimators are established. Moreover, we also study variable selection by adopting the coordinate-independent sparse estimation to select all relevant but distorted covariates in the parametric part. We show that the resulting sparse estimators can exclude all irrelevant covariates with probability approaching one. A simulation study is conducted to evaluate the performance of the proposed methods and a real data set is analyzed for illustration.     

Unbiased Recursive Partitioning: A Conditional Inference Framework

Recursive binary partitioning is a popular tool for regression analysis. Two fundamental problems of exhaustive search procedures usually applied to fit such models have been known for a long time: overfitting and a selection bias towards covariates with many possible splits or missing values. While pruning procedures are able to solve the overfitting problem, the variable selection bias still seriously affects the interpretability of tree-structured regression models. For some special cases unbiased procedures have been suggested, however lacking a common theoretical foundation. We propose a unified framework for recursive partitioning which embeds tree-structured regression models into a well defined theory of conditional inference procedures. Stopping criteria based on multiple test procedures are implemented and it is shown that the predictive performance of the resulting trees is as good as the performance of established exhaustive search procedures. It turns out that the partitions and therefore the models induced by both approaches are structurally different, confirming the need for an unbiased variable selection. Moreover, it is shown that the prediction accuracy of trees with early stopping is equivalent to the prediction accuracy of pruned trees with unbiased variable selection. The methodology presented here is applicable to all kinds of regression problems, including nominal, ordinal, numeric, censored as well as multivariate response variables and arbitrary measurement scales of the covariates. Data from studies on glaucoma classification, node positive breast cancer survival and mammography experience are re-analyzed.     

Variable selection and model choice in structured survival models

We aim at modeling the survival time of intensive care patients suffering from severe sepsis. The nature of the problem requires a flexible model that allows to extend the classical Cox-model via the inclusion of time-varying and nonparametric effects. These structured survival models are very flexible but additional difficulties arise when model choice and variable selection are desired. In particular, it has to be decided which covariates should be assigned time-varying effects or whether linear modeling is sufficient for a given covariate. Component-wise boosting provides a means of likelihood-based model fitting that enables simultaneous variable selection and model choice. We introduce a component-wise, likelihood-based boosting algorithm for survival data that permits the inclusion of both parametric and nonparametric time-varying effects as well as nonparametric effects of continuous covariates utilizing penalized splines as the main modeling technique. An empirical evaluation of the methodology precedes the model building for the severe sepsis data. A software implementation is available to the interested reader.     

Covariate Transformation Diagnostics for Generalized Linear Models

Transformations of covariates are commonly applied in regression analysis. When a parametric transformation family is used, the maximum likelihood estimate of the transformation parameter is often sensitive to minor perturbations of the data. Diagnostics are derived to assess the influence of observations on the covariate transformation parameter in generalized linear models. Three numerical examples are presented to illustrate the usefulness of the proposed diagnostics.