具有部分缺失数据时两个威布尔分布的估计和检验

文中讨论了部分缺失数据两威布尔总体的参数估计和关于总体相同的似然比检验．证明估计的强相合性和渐近正态性,给出似然比检验统计量的极限分布,并探讨了基于精确分布的检验问题．     

Estimation of Item Response Theory Parameters in the Presence of Missing Data

Missing data are a common problem in a variety of measurement settings, including responses to items on both cognitive and affective assessments. Researchers have shown that such missing data may create problems in the estimation of item difficulty parameters in the Item Response Theory (IRT) context, particularly if they are ignored. At the same time, a number of data imputation methods have been developed outside of the IRT framework and been shown to be effective tools for dealing with missing data. The current study takes several of these methods that have been found to be useful in other contexts and investigates their performance with IRT data that contain missing values. Through a simulation study, it is shown that these methods exhibit varying degrees of effectiveness in terms of imputing data that in turn produce accurate sample estimates of item difficulty and discrimination parameters.     

因变量缺失的变系数部分线性模型的有效估计

讨论了因变量随机缺失条件下变系数部分线性模型的估计问题。基于局部借补思想,使用局部线性方法和平均技巧同时得到了各个估计量的估计,进而给出了估计的渐近性质。     

缺失数据的处理和挑战

在数据挖掘研究中,缺失数据是一个非常普遍的问题,如何处理缺失数据也是一个热门的研究领域．介绍了缺失数据产生的原因,分类总结了缺失数据的处理方法,最后,提出了处理缺失数据的一些挑战性课题。     

两个0-1总体具有部分缺失数据时的估计和检验

文章主要讨论了两个0-1总体均具有部分缺失数据时的参数的极大似然估计,并证明了估计的强相合性和渐进正态性,给出了大样本场合下的似然比检验统计量的极限分布。     

不同背景颜色对阅读理解的影响

目的:探讨不同背景颜色对大学生阅读理解的影响情况。方法:从福建某大学选取160名大一学生为被试,采用4×2被试间设计,以ppt的形式呈现中文材料阅读,以此考察大学生的阅读成绩。结果:(1)不同背景颜色存在显著差异(F=4.731,p=.003),其中白色背景的阅读成绩高于红、绿、蓝背景;(2)字体大小差异不显著(F=1.104,p=.295),背景色和字体大小交互作用不显著(F=2.156,p=.096)。结论:颜色对阅读成绩产生影响,字体大小对阅读成绩不产生影响。     

On Testability of Missing Data Mechanisms in Incomplete Data Sets

This article is concerned with the question of whether the missing data mechanism routinely referred to as missing completely at random (MCAR) is statistically examinable via a test for lack of distributional differences between groups with observed and missing data, and related consequences. A discussion is initially provided, from a formal logic standpoint, of the distinction between necessary conditions and sufficient conditions. This distinction is used to argue then that testing for lack of these group distributional differences is not a test for MCAR, and an example is given. The view is next presented that the desirability of MCAR has been frequently overrated in empirical research. The article is finalized with a reference to principled, likelihood-based methods for analyzing incomplete data sets in social and behavioral research.     

The Impact of Background Television on Parent–Child Interaction

This study investigated the hypothesis that background television affects interactions between parents and very young children. Fifty-one 12-, 24-, and 36-month-old children, each accompanied by 1 parent, were observed for 1 hr of free play in a laboratory space resembling a family room. For half of the hour, an adult-directed television program played in the background on a monaural television set. During the other half hour, the television was not on. Both the quantity and quality of parent–child interaction decreased in the presence of background television. These findings suggest one way in which early, chronic exposure to television may have a negative impact on development.     

缺失数据的插补调整方法

统计调查中,经常会遇到数据缺失的现象．缺失数据会影响统计分析的质量．文中提出了一种先对数据的缺失机制进行统计检验,针对是否存在显著分布偏性,分别采取相应的插补算法的统计方法．该系统算法可以全面处理离散数据和时间序列数据的不同缺失机制的缺失数据．     

数据库索引对数据操作的影响

在SQL Server表上使用索引对数据操作性能非常关键,有效地设计索引可以提高SQL Serv-er系统的性能。不合理的使用索引不仅会使表的操作速度明显变慢,而且会使数据检索的速度降低。因此,要创建合适的索引以提高数据库的性能。     

文化背景对翻译的影响

翻译既是跨语言的活动,也是跨文化的活动,语言与文化之间具有不可分割的关系.没有语言,文化就不可能存在,语言也只有反映文化才有意义.翻译过程中,译者不但要精通两国的语言,还必须具有深厚的文化功底,能深刻理解两种文化的异同.只有这样,才能做到不仅语言意义上等值,而且文化意义上等值.文章从文化背景对翻译的影响入手,分析了正确处理两者关系的方法.     

背景音乐对学习的影响研究

从背景音乐对学习的影响,背景音乐对认知的影响,背景音乐影响作用的生理、心理机制四方面探讨背景音乐对学习和认知的影响,同时针对研究中的结果提出教学建议,以便学校能够为学生创设良好的学习情境,为提高教与学的效率提供依据。     

大数据背景下公共数据资源运用探析

我国数据资源主要集中于政府部门手中,这会诱发一系列问题,一方面,政府部门将数据资源束之高阁导致数据资源严重浪费,另一方面,公共数据资源开发力度不够以及公共数据开放中导致公民信息泄露问题都成为制约大数据发展的重要障碍.因此,建立健全大数据相关运用立法、加强数据运用监管、提高政府部门和社会公众的数据意识,形成数据文化,是推动大数据产业发展所必需.     

Effects of Missing Data Methods in Structural Equation Modeling With Nonnormal Longitudinal Data

The purpose of this study is to investigate the effects of missing data techniques in longitudinal studies under diverse conditions. A Monte Carlo simulation examined the performance of 3 missing data methods in latent growth modeling: listwise deletion (LD), maximum likelihood estimation using the expectation and maximization algorithm with a nonnormality correction (robust ML), and the pairwise asymptotically distribution-free method (pairwise ADF). The effects of 3 independent variables (sample size, missing data mechanism, and distribution shape) were investigated on convergence rate, parameter and standard error estimation, and model fit. The results favored robust ML over LD and pairwise ADF in almost all respects. The exceptions included convergence rates under the most severe nonnormality in the missing not at random (MNAR) condition and recovery of standard error estimates across sample sizes. The results also indicate that nonnormality, small sample size, MNAR, and multicollinearity might adversely affect convergence rate and the validity of statistical inferences concerning parameter estimates and model fit statistics.     

指数分布无失效数据参数的Bayes估计

本文对指数分布的无失效数据,在引进失效信息后,在参数的先验分布为不完全Beta分布和指数型分布时,给出了参数的多层Bayes估计和综合Bayes估计,从而可以得到可靠度的估计.     

无失效数据的Logistic分布参数的最小二乘估计及可靠度的估计

本文给出在无失效数据情况下,当产品寿命服从Logistic分布时,产品寿命的失效率=(<)i ip P t t的参数的最小二乘估计与产品可靠度的估计。     

失踪的兔子

<正>It was pancake day.The city mayor~1 was sitting up in bed eating his breakfast—a big pancake,when his mobile phone rang.How he hated it when people called him while he was still at breakfast! Then he saw that the call was coming from the chief~2 of police.今天是煎饼日。市长坐在床上吃早餐——一个大煎饼,这时他的手机响了。他是多么讨厌人们在他还在吃早餐的时候给他打电话!然后他看到电话是警察局长打来的。     

The Missing Sunglasses

was late. She found her purse. She found her keys. But she could not find her. She asked , Have you seen my?