Testing the equality of several covariance matrices

Using a new approach based on Meijer G-functions and computer simulation, we numerically compute the exact null distribution of the modified-likelihood ratio statistic used to test the hypothesis that several covariances matrices of normal distributions are equal. Small samples of different sizes are considered, and for the case of two matrices, we introduce a new test based on determinants, with the null distribution of its criterion also fully computable. Comparisons with published results show the accuracy of our approach, which is proved to be more flexible and adaptable to different cases.     

On a paper by kageyama and mohan

Kageyama Mohan (1984) have presented three methods of constructing new incomplete block designs from balanced incomplete block designs, They raise questions about the designs which come from each of their methods, These questions are answered, Another series of group divisible designs is derived as a special case of their second method.     

创新让你的作文更美

千篇一律的文章令人生厌。创新能增加文章魅力,我们应该重视创新,作文才能给人耳目一新的感觉,给人带来美的享受。要使文章更美,可从立意、构思、选材、拟题这四个方面创新着手。     

An L1-type estimator of multivariate location and shape

The main goal of the paper is to specify a suitable multivariate multilevel model for polytomous responses with a non-ignorable missing data mechanism in order to determine the factors which influence the way of acquisition of the skills of the graduates and to evaluate the degree programmes on the basis of the adequacy of the skills they give to their graduates. The application is based on data gathered by a telephone survey conducted, about two years after the degree, on the graduates of year 2000 of the University of Florence. A multilevel multinomial logit model for the response of interest is fitted simultaneously with a multilevel logit model for the selection mechanism by means of maximum likelihood with adaptive Gaussian quadrature. In the application the multilevel structure has a crucial role, while selection bias results negligible. The analysis of the empirical Bayes residuals allows to detect some extreme degree programmes to be further inspected.     

Mixing patterns between age groups in social networks

We present a method for estimating transmission matrices that describe the mixing and the probability of infection between age groups. Transmission matrices can be used to estimate age-dependent forces of infection in age-structured, compartmental models for the study of infectious diseases. We analyze the social network generated by the synthetic population of Portland and extract mixing patterns. Our results show that the mixing within the population consists of two groups, children and adults. Children interact most frequently with other children close to their own age, while adults interact with a wider range of age groups and the durations of typical adult contacts are shorter than typical contacts between children. Furthermore, the transmission matrix shows that children are more likely to acquire infection than adults.     

线性异或逻辑方程组和逻辑矩阵

线性异或逻辑方程组现有的求解方法均不适于用计算机求解。为此,本文引入了逻辑矩阵的概念。本文对逻辑矩阵、逻辑向量系的相关性、Cramer法则等进行了理论证明或分析。     

Bellman猜想在四元数体上的修正

在四元数体上修正了关于矩阵迹的Ｂｅｌｌｍａｎ不等式，并利用广义酉空间的理论，证明了几个四元数阵矩阵之迹的不等式。     

带核实赋值环上的多项式矩阵

本文旨在研究带核实赋值环上的多项式矩阵．在本文中，关于带核实赋值环上的多项式矩阵的半代数点定理被建立，同时正定矩阵与半正定矩阵的平方和表示也得到表明．     

《元曲选》宾白中的"些""些儿""一些(儿)"(下)

"些儿"的语法功能是作定语、宾语、补语,其语法意义或表事物、动作不定的少量,或指示性状比较的轻微程度,还可表动作时间的短暂;"些"与"些儿"有同有异。"一些(儿)"可作主语、定语、宾语、状语,一般用于否定句,其语法意义是表极少量。在量的多少上,似形成"一些(儿)<些儿<些"的差异。     

A new 'biased coin design' for the sequential allocation of two treatments

Summary.  Efron's biased coin design is a well-known randomization technique that helps to neutralize selection bias in sequential clinical trials for comparing treatments, while keeping the experiment fairly balanced. Extensions of the biased coin design have been proposed by several researchers who have focused mainly on the large sample properties of their designs. We modify Efron's procedure by introducing an adjustable biased coin design, which is more flexible than his. We compare it with other existing coin designs; in terms of balance and lack of predictability, its performance for small samples appears in many cases to be an improvement with respect to the other sequential randomized allocation procedures.