Multivariate normal estimation: the case (n < p)

Estimation in the multivariate context when the number of observations available is less than the number of variables is a classical theoretical problem. In order to ensure estimability, one has to assume certain constraints on the parameters. A method for maximum likelihood estimation under constraints is proposed to solve this problem. Even in the extreme case where only a single multivariate observation is available, this may provide a feasible solution. It simultaneously provides a simple, straightforward methodology to allow for specific structures within and between covariance matrices of several populations. This methodology yields exact maximum likelihood estimates.     

Tail asymptotic of discounted aggregate claims with compound dependence under risky investment

This paper considers the tail asymptotic of discounted aggregate claims with compound dependence under risky investment. The price of risky investment is modeled by a geometric Lévy process, while claims are modeled by a one-sided linear process whose innovations further obeying a so-called upper tail asymptotic independence. When the innovations are heavy tailed, we derive some uniform asymptotic formulas. The results show that the linear dependence has significant impact on the tail asymptotic of discounted aggregate claims but the upper tail asymptotic independence is negligible.     

我国学前教育地方立法研究

学前教育地方立法是我国学前教育立法体系的有机组成部分，截至2020 年1 月，我国现行有效的学前教育地方性法规 规章共61 部，呈现出立法时间跨度大，立法主体覆盖面广，立法模式体例多样等特征。地方立法一定程度上规范着地方学前 教育的有序开展，但也存在部分省市立法机关对当地学前教育立法关注度不高、部分立法难以满足当前学前教育发展需求、表 达不规范、可操作性欠佳、缺乏地方特色以及冲突与越位等问题。对此，应从科学确定学前教育地方立法内容、建立地方性法 律适时更新制度、健全学前教育地方立法调研制度、加强地方立法专业化制度建设等方面予以优化。     

Bayesian estimation of reliability using time-to-failure distribution of parametric degradation models

This paper focusses on computing the Bayesian reliability of components whose performance characteristics (degradation – fatigue and cracks) are observed during a specified period of time. Depending upon the nature of degradation data collected, we fit a monotone increasing or decreasing function for the data. Since the components are supposed to have different lifetimes, the rate of degradation is assumed to be a random variable. At a critical level of degradation, the time to failure distribution is obtained. The exponential and power degradation models are studied and exponential density function is assumed for the random variable representing the rate of degradation. The maximum likelihood estimator and Bayesian estimator of the parameter of exponential density function, predictive distribution, hierarchical Bayes approach and robustness of the posterior mean are presented. The Gibbs sampling algorithm is used to obtain the Bayesian estimates of the parameter. Illustrations are provided for the train wheel degradation data.     

A class of partially linear transformation models for recurrent gap times

In this article, we propose a general class of partially linear transformation models for recurrent gap time data, which extends the linear transformation models by incorporating non linear covariate effects and includes the partially linear proportional hazards and the partially linear proportional odds models as special cases. Both global and local estimating equations are developed to estimate the parametric and non parametric covariate effects, and the asymptotic properties of the resulting estimators are established. The finite-sample behavior of the proposed estimators is evaluated through simulation studies, and an application to a clinic study on chronic granulomatous disease is provided.     

Sample size re‐estimation incorporating prior information on a nuisance parameter

Prior information is often incorporated informally when planning a clinical trial. Here, we present an approach on how to incorporate prior information, such as data from historical clinical trials, into the nuisance parameter–based sample size re‐estimation in a design with an internal pilot study. We focus on trials with continuous endpoints in which the outcome variance is the nuisance parameter. For planning and analyzing the trial, frequentist methods are considered. Moreover, the external information on the variance is summarized by the Bayesian meta‐analytic‐predictive approach. To incorporate external information into the sample size re‐estimation, we propose to update the meta‐analytic‐predictive prior based on the results of the internal pilot study and to re‐estimate the sample size using an estimator from the posterior. By means of a simulation study, we compare the operating characteristics such as power and sample size distribution of the proposed procedure with the traditional sample size re‐estimation approach that uses the pooled variance estimator. The simulation study shows that, if no prior‐data conflict is present, incorporating external information into the sample size re‐estimation improves the operating characteristics compared to the traditional approach. In the case of a prior‐data conflict, that is, when the variance of the ongoing clinical trial is unequal to the prior location, the performance of the traditional sample size re‐estimation procedure is in general superior, even when the prior information is robustified. When considering to include prior information in sample size re‐estimation, the potential gains should be balanced against the risks.     

土地流转中为什么会形成大量小农复制

土地流转是实现规模化经营的前提之一,然而土地流转中却出现大量小农复制,从而影响土地流转的质量和效果。运用12省(自治区)2 553份农户问卷,详细分析土地流转中小农复制的现状及其形成原因。研究发现：(1)农户流转耕地面积不大,转入户流转面积20亩及以下的约占总转入户数的60.3％,转出户流转面积5亩及以下的约占总转出户数的74.38％,转出户中仍然经营土地的约占总转出户数的74％。(2)农业分工发达使生产更加方便、文化传统形成路径依赖、禀赋效应产生“价值幻觉”以及公共服务不健全使未来存在不确定性导致转出户流转部分土地。乡土社会限制土地流转范围和经营风险增加风险感知导致转入户流转小规模土地。     

新时代应用型教师的培养：问题与策略——以地方本科院校为视角

以校地合作、校企合作为发展战略的地方本科院校向应用型院校转变，已经成为一种潮流和趋势，而应用型教师的建设与培养更是迫在眉睫。在明确新时代高校应用型教师培养的必要性的基础上，从数量层面、结构层面、能力层面以及培训层面指出了培养过程中存在的问题，同时针对这些问题提出较为有效的应对策略。