电流互感器取油样连接阀的研制

对于顶珠式放油阀的电流互感器,取样时靠人工顶住顶珠取油,既操作不便且样本不准确,同时在不停电取样时容易因感应电造成人身伤害,为此研制了一种取样连接阀.经实践验证,这种简便、灵活、实用的电流互感器取油样阀,克服了以上取样的不足.     

Multimediation Method With Balanced Repeated Replications For Analysis Of Complex Surveys

We propose a method suitable for analysis of cross-sectional studies with complex sampling and continuous variables. The method consists of R + 4 steps, where R denotes the number of replications. In the first R + 1 step, the main and R replicate weights are used (one at a time) to estimate the product of coefficients for all mediation effects using a structural equation model. In step R + 2, the standard errors of these estimates are computed via balanced repeated replications. In step R + 3, the raw p values corresponding to mediation effects are computed based on the generalized Sobel’s tests. In the final step, R + 4, the p values are adjusted for multiplicity and statistical inferences regarding mediation effects are drawn. To illustrate the approach we examined significance of attitudes toward smoking bans as mediators in the association between smoking restrictions at work and nicotine dependence among male daily smokers.     

Designing Intervention Studies: Selected Populations,Range Restrictions,and Statistical Power

ABSTRACT

An appropriate estimate of statistical power is critical for the design of intervention studies. Although the inclusion of a pretest covariate in the test of the primary outcome can increase statistical power, samples selected on the basis of pretest performance may demonstrate range restriction on the selection measure and other correlated measures. This can result in attenuated pretest–posttest correlations, reducing the variance explained by the pretest covariate. We investigated the implications of two potential range restriction scenarios: direct truncation on a selection measure and indirect range restriction on correlated measures. Empirical and simulated data indicated that direct range restriction on the pretest covariate greatly reduced statistical power and necessitated sample size increases of 82%–155% (dependent on selection criteria) to achieve equivalent statistical power to parameters with unrestricted samples. However, measures demonstrating indirect range restriction required much smaller sample size increases (32%–71%) under equivalent scenarios. Additional analyses manipulated the correlations between measures and pretest–posttest correlations to guide planning experiments. Results highlight the need to differentiate between selection measures and potential covariates and to investigate range restriction as a factor impacting statistical power.     

The balance and imbalance of sampling former teachers hidden-by-choice: a snowball in summer

ABSTRACT

In this paper, we explore the challenges inherent in conducting research with a hidden population – how to conduct research with teachers who have left the classroom. Capturing the storied experiences of this group is vital to understanding how to effectively recruit, prepare, support, and sustain teachers in US classrooms for our next generation of students. Although not typically considered vulnerable, this population of “teacher leavers” remains hidden-by-choice because of a voluntary severing of ties with former schools and school districts. In this paper, we chronicle our efforts to identify an appropriate sampling method for this population, our selection of snowball sampling because of the hidden nature of individuals, and our efforts to use snowball sampling to construct a national sample of teacher leavers. We conclude by identifying the resulting areas of balance and imbalance in our sample, their possible explanations, and their subsequent implications for informing thoughtful sampling methodology.     

Planning the Digital Public Library of America

By using barcodes to identify random lists of books, taking small monthly samples, and updating a simple control chart, the authors outline a simple, effective way (1) to chart the reasons why books aren't available; (2) to gauge if changes in procedures are needed; and (3) to determine if such changes are successful.     

非参数bootstrap方法及其MATLAB实现

介绍非参数bootstrap方法的实现步骤,并通过具体实例,利用MATLAB强大的编程和计算功能实现了非参数bootstrap方法。     

不平衡数据集分类方法研究

本文主要介绍了不平衡数据分类的方法,包括数据层面的方法和算法改进方面的方法;传统的分类方法的评价指标,对于不平衡数据集是不适用的,故本文最后又对不平衡数据集分类的评价指标作了简要的探讨。     

体育科研中有关问卷调查值得注意的问题

针对体育科研中运用问卷调查法还不够完善这一现象,提出了几个应该注意的问题:明确抽样的总体;进行问卷的信度和效度的检验;说明选择抽样的方法;控制抽样误差;试调查不可忽略等几个方面,并做了一些分析,以期引起大家的注意.     

体育社会科学硕士研究生论文中使用统计方法的调查与分析

把20世纪90年代以来北京体育大学体育社会科学研究生的学位论文作为研究对象,分析探讨了其中使用统计方法出现的问题,并指出正确的应用方法,以利于体育科学研究的科学性.研究结果显示:90年代早期的论文,统计方法使用少、简单、错误率高;而90年代晚期的论文,使用的统计方法越来越多,初级统计方法错误率趋减.     

方差分析中单项效应的抽样分布

应用正态向量及独立随机向量的有关性质直接给出了方差分析中单项效应的抽样分布。但传统的证明方法(利用柯赫伦定理(Cochran))只给出了间接的证明,而这也正是“方差分析”中特别需要解决的问题。