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51.
We revisit the problem of testing homoscedasticity (or, equality of variances) of several normal populations which has applications in many statistical analyses, including design of experiments. The standard text books and widely used statistical packages propose a few popular tests including Bartlett's test, Levene's test and a few adjustments of the latter. Apparently, the popularity of these tests have been based on limited simulation study carried out a few decades ago. The traditional tests, including the classical likelihood ratio test (LRT), are asymptotic in nature, and hence do not perform well for small sample sizes. In this paper we propose a simple parametric bootstrap (PB) modification of the LRT, and compare it against the other popular tests as well as their PB versions in terms of size and power. Our comprehensive simulation study bursts some popularly held myths about the commonly used tests and sheds some new light on this important problem. Though most popular statistical software/packages suggest using Bartlette's test, Levene's test, or modified Levene's test among a few others, our extensive simulation study, carried out under both the normal model as well as several non-normal models clearly shows that a PB version of the modified Levene's test (which does not use the F-distribution cut-off point as its critical value), and Loh's exact test are the “best” performers in terms of overall size as well as power. 相似文献
52.
For many continuous distributions, a closed-form expression for their quantiles does not exist. Numerical approximations for their quantiles are developed on a distribution-by-distribution basis. This work develops a general approximation for quantiles using the Taylor expansion. Our method only requires that the distribution has a continuous probability density function and its derivatives can be derived to a certain order (usually 3 or 4). We demonstrate our unified approach by approximating the quantiles of the normal, exponential, and chi-square distributions. The approximation works well for these distributions. 相似文献
53.
徐畅 《江苏大学学报(高教研究版)》2010,(1):23-27,32
为了贯彻《共同纲领》的文教政策,使山东大学顺利实现向新民主主义大学的转变,在建国初期山东大学思想政治教育中,校长华岗为全校师生所授政治大课,采取理论联系实际和以理服人的方针,系统地给山大师生讲授了党的政策和马克思主义基本原理,提高了山大师生的觉悟,为20世纪50年代山大的辉煌奠定了基础。 相似文献
54.
Mixed-Weibull distribution has been used to model a wide range of failure data sets, and in many practical situations the number of components in a mixture model is unknown. Thus, the parameter estimation of a mixed-Weibull distribution is considered and the important issue of how to determine the number of components is discussed. Two approaches are proposed to solve this problem. One is the method of moments and the other is a regularization type of fuzzy clustering algorithm. Finally, numerical examples and two real data sets are given to illustrate the features of the proposed approaches. 相似文献
55.
Methods for a sequential test of a dose-response effect in pre-clinical studies are investigated. The objective of the test procedure is to compare several dose groups with a zero-dose control. The sequential testing is conducted within a closed family of one-sided tests. The procedures investigated are based on a monotonicity assumption. These closed procedures strongly control the familywise error rate while providing information about the shape of the dose-responce relationship. Performance of sequential testing procedures are compared via a Monte Carlo simulation study. We illustrae the procedures by application to a real data set. 相似文献
56.
新经济地理学视域下,边境不再是人为阻隔生产要素流动的非贸易壁垒,而是促进国际专业化分工和形成循环因果积累效应的天然地理因素。基于新经济地理学的相关理论,研究中印边境贸易的专业化模式和贸易模式以及边境贸易政策对中印边境贸易的影响,以论证中印两国经贸的比较优势在边境地区的空间整合,最终推动中印边境贸易健康发展。 相似文献
57.
Youngjae Chang 《统计学通讯:模拟与计算》2013,42(8):1703-1726
Many tree algorithms have been developed for regression problems. Although they are regarded as good algorithms, most of them suffer from loss of prediction accuracy when there are many irrelevant variables and the number of predictors exceeds the number of observations. We propose the multistep regression tree with adaptive variable selection to handle this problem. The variable selection step and the fitting step comprise the multistep method. The multistep generalized unbiased interaction detection and estimation (GUIDE) with adaptive forward selection (fg) algorithm, as a variable selection tool, performs better than some of the well-known variable selection algorithms such as efficacy adaptive regression tube hunting (EARTH), FSR (false selection rate), LSCV (least squares cross-validation), and LASSO (least absolute shrinkage and selection operator) for the regression problem. The results based on simulation study show that fg outperforms other algorithms in terms of selection result and computation time. It generally selects the important variables correctly with relatively few irrelevant variables, which gives good prediction accuracy with less computation time. 相似文献
58.
大学生是微信最忠实的拥趸,“微信热”不仅给大学生的工作和生活带来了诸多影响,同时也给高校思想政治教育工作带来了严峻挑战。微信的不可控性,使高校思想政治教育环境趋于复杂;微信立体化的社交形式,使高校思想政治教育方法受到挑战;微信的虚拟性,使高校思想政治教育过程难度加大;微信信息的“碎片化”,削弱了高校思想政治教育实效性。在“微信热”背景下,探讨其产生的深层原因,科学应对微信带来的挑战,运用微信进行“微创新”、发挥“微功能”,对大学生思想政治教育意义重大。 相似文献
59.
60.
技术改造及其项目管理是大型航空制造企业经营管理活动中的重要任务之一。企业通过技术 改造项目改进生产条件和生产工艺,增强军民用航空产品的研制能力。论文根据技改项目管 理的特点,运用系统动力学方法建立技改项目全生命周期动力学模型,对技改项目生命周期 的全过程进行动态仿真,为管理者提供信息和决策支持。最后,结合工作流技术的优点,建 立了基于工作流技术的技改项目管理协同平台原型 相似文献