The 'improved' brown and forsythe test for mean equality: some things can't be fixed

Mehrotra (1997) presented an ‘;improved’ Brown and Forsythe (1974) statistic which is designed to provide a valid test of mean equality in independent groups designs when variances are heterogeneous. In particular, the usual Brown and Fosythe procedure was modified by using a Satterthwaite approximation for numerator degrees of freedom instead of the usual value of number of groups minus one. Mehrotra then, through Monte Carlo methods, demonstrated that the ‘improved’ method resulted in a robust test of significance in cases where the usual Brown and Forsythe method did not. Accordingly, this ‘improved’ procedure was recommended. We show that under conditions likely to be encountered in applied settings, that is, conditions involving heterogeneous variances as well as nonnormal data, the ‘improved’ Brown and Forsythe procedure results in depressed or inflated rates of Type I error in unbalanced designs. Previous findings indicate, however, that one can obtain a robust test by adopting a heteroscedastic statistic with the robust estimators, rather than the usual least squares estimators, and further improvement can be expected when critical significance values are obtained through bootstrapping methods.     

Robust test for means when population variances are unequal

We consider the problem of testing the equality of two population means when the population variances are not necessarily equal. We propose a Welch-type statistic, say T^* _c, based on Tiku!s ‘1967, 1980’ modified maximum likelihood estimators, and show that this statistic is robust to symmetric and moderately skew distributions. We investigate the power properties of the statistic T^* _c; T^* _c clearly seems to be more powerful than Yuen's ‘1974’ Welch-type robust statistic based on the trimmed sample means and the matching sample variances. We show that the analogous statistics based on the ‘adaptive’ robust estimators give misleading Type I errors. We generalize the results to testing linear contrasts among k population means     

一类二阶非线性差分方程正解的存在性

主要利用推广的Riccati变换,建立了一类比较广泛的二阶非线性差分方程正解存在的充分和必要条件.     

一类一阶线性方程组的解法

利用复系数的一阶线性方程解公式，给出一类一阶线性方程组的新解性。     

具反射边界条件的板模型迁移系统的临界性

研究非均匀介质,各向同性,具反射边界条件的板模型迁移系统的临界解.借助泛函分析方法,特别是Lp空间上的线性算子理论,证明了积分算子的主本征值(即临界参数)的性质,并获得了系统处于次临界状态的条件以及使系统处于临界状态的板厚度的存在性.     

几种药物对降低尿素分解液中氨浓度的试验

在相同的外界条件下,在相同浓度的等量脲酶尿素液中加入脲酶抑制剂、吸附剂,在不同时间进行pH值和NH_3—N值的测定,研究各药物对降低氨浓度的强弱。结果表明:各试验组氨浓度极显著低于对照组(P<0.01);在添加剂量相同的情况下,脲酶抑制剂和药用炭的作用较强(P<0.05),二者之间差异不显著(P>0.05);浮石、滑石粉、BIO—ADE作用较弱且三者之间差异不显著(P>0.05),三者中以选择滑石粉较好(价格较便宜)。     

数值解法的另一种欧拉改进法

在求常微分方程初值问题的数值解时,本文在欧拉方法计算结果上再补充一个拉格朗日余项的近似值,以期达到提高精确度的效果,并由此而构造了一个新的计算格式.     

跨国公司扩大对华R&D投资的影响与对策

跨国公司在华R＆D投资的发展会对我国的企业、产业、技术创新和技术进步带来什么样的影响?能否达到我国吸引跨国公司R＆D投资所期望的战略目标和层次?这是人们所普遍关心和想深入了解的一个问题。本文探讨了跨国公司在华R＆D投资的内在动因与挑战问题;分析了我国吸引跨国公司R＆D投资的多重需求和效应;提出了促使我国吸引跨国公司R＆D投资有效目标实现的应对策略。     

关于完善我国失业保险制度促进就业功能的思考

在当前社会转型期,失业保险是我国面临的非常重要的问题之一。我国目前的失业保险制度在促进就业方面存在着不足。应该借鉴国外的成功经验并结合我国的具体实际,在调整失业保险制度理念、适时提高统筹层次、完善就业服务机制等方面进行改进,不断完善我国失业保险制度,发挥它在促进就业中的作用。     

生物聚合物溶液中悬浮微粒渗流模拟研究

本文采用数值模拟并结合物理模拟两种手段对生物聚台物溶液中悬浮微粒的驱油渗流动态进行了探讨。物理实验发现,所用的生物聚合物溶液中的悬浮微粒在多孔介质中进行运移,并被捕集,因而引起溶液在介质中的渗透率显著下降。作者根据 C—H简化模型及物理模拟实验模型,建立了一套简单的数学模型,通过数值计算方法对所要分析的堵塞情况进行了数值模拟,从而对生物聚合物溶液中悬浮微粒在驱油过程的渗流规律进行了探讨。