The Power of the Test for Treatment Effects in Three-Level Cluster Randomized Designs

Abstract

Experiments that involve nested structures often assign entire groups (such as schools) to treatment conditions. Key aspects of the design of such experiments include knowledge of the intraclass correlation structure and the sample sizes necessary to achieve adequate power to detect the treatment effect. This study provides methods for computing power in three-level cluster randomized balanced designs (with two levels of nesting), where, for example, students are nested within classrooms and classrooms are nested within schools and schools are assigned to treatments. The power computations take into account nesting effects at the second (classroom) and at the third (school) level, sample size effects (e.g., number of schools, classrooms, and individuals), and covariate effects (e.g., pretreatment measures). The methods are applicable to quasi-experimental studies that examine group differences in an outcome.     

A More Powerful Test in Three-Level Cluster Randomized Designs

Abstract

Field experiments that involve nested structures frequently assign treatment conditions to entire groups (such as schools). A key aspect of the design of such experiments includes knowledge of the clustering effects that are often expressed via intraclass correlation. This study provides methods for constructing a more powerful test for the treatment effect in three-level cluster randomized designs with two levels of nesting (at the second and third levels). When the intraclass correlation structure at the second and third level is assumed to be known, the proposed test provides higher estimates of power than those obtained from the typical test based on level-3 unit means, because it preserves the degrees of freedom associated with the number of level-2 and level-1 units. The advantage in power estimates is more pronounced when the number of level-3 units (e.g., schools) is small and the samples are homogeneous (e.g., low-achieving schools).     

Power Analysis in Two-Level Unbalanced Designs

Previous work on statistical power has discussed mainly single-level designs or 2-level balanced designs with random effects. Although balanced experiments are common, in practice balance cannot always be achieved. Work on class size is one example of unbalanced designs. This study provides methods for power analysis in 2-level unbalanced designs with random effects. Overall, the nesting affects power negatively, the treatment affects power positively, and the Level-2 units affect power more than Level-1 units. Computing power assuming balanced designs provides reasonable estimates only when imbalance is mild or moderate. When imbalance is large or extreme, computing power assuming balanced designs produces larger estimates of power. The use of the harmonic mean provides accurate estimates of power in unbalanced 2-level designs even when imbalance is large.     

Statistical Power of Randomization Tests Used with Multiple-Baseline Designs

Statistical power was estimated for 3 randomization tests used with multiple-baseline designs. In 1 test, participants were randomly assigned to baseline conditions; in the 2nd, intervention points were randomly assigned; and in the 3rd, the authors used both forms of random assignment. Power was studied for several series lengths (N = 10, 20, 30), several effect sizes (d = 0, 0.5, 1.0, 1.5, 2.0), and several levels of autocorrelation among the errors (p ₁ = 0, .1, .2, .3, .4, and .5). Power was found to be similar among the 3 tests. Power was low for effect sizes of 0.5 and 1.0 but was often adequate (> .80) for effect sizes of 1.5 and 2.0.     

试论期刊设计中色彩的市场效应

色彩是期刊设计中最为直观也最具想象力的因素 ,它以其自身的机能和内在规律 ,在现代期刊装帧设计中发挥着愈来愈重要的作用 ,尤其体现在市场效应上 ,色彩的意义是其他形式不可替代的 .以几种杂志的装帧设计为例 ,具体阐述了色彩在期刊设计中的市场效应     

Accuracy of Estimates and Statistical Power for Testing Meditation in Latent Growth Curve Modeling

The latent growth curve modeling (LGCM) approach has been increasingly utilized to investigate longitudinal mediation. However, little is known about the accuracy of the estimates and statistical power when mediation is evaluated in the LGCM framework. A simulation study was conducted to address these issues under various conditions including sample size, effect size of mediated effect, number of measurement occasions, and R ₂ of measured variables. In general, the results showed that relatively large samples were needed to accurately estimate the mediated effects and to have adequate statistical power, when testing mediation in the LGCM framework. Guidelines for designing studies to examine longitudinal mediation and ways to improve the accuracy of the estimates and statistical power were discussed.     

室内设计中的人体工程学分析

过去人们研究探讨室内设计问题,经常把人与物、人与环境孤立地对待,认为人就是人,物就是物,环境也就是环境,或者单纯地以人去适应物和环境·而随着人们物质生活与精神生活的发展,现代室内设计日益重视人与物和环境之间以人为主体的协调,也就是说,设计师在进行室内设计时,应重视以人为中心的视觉环境、物理环境、生理环境以及心理环境的综合研究·     

工程力学教学中的几点设计

专业基础课与学生的学习兴趣和能力之间有一定的距离,如何能够唤起并始终保持学生适度的学习兴趣,需要教师对教学的方方面面进行精心设计.     

母语在ESL课程设计中的正迁移作用

母语思维是二语习得领域关心的问题。从语言学习的本质、母语学习对二语习得的内在联系来看,母语思维在一定程度上有助于二语习得,因此在ESL课程设计中,应充分发挥母语的正迁移作用,其中涉及到语音、词汇、句法等多种层面。     

Distributional Analysis in Educational Evaluation: A Case Study from the New York City Voucher Program

We use quantile treatment effects estimation to examine the consequences of the random-assignment New York City School Choice Scholarship Program across the distribution of student achievement. Our analyses suggest that the program had negligible and statistically insignificant effects across the skill distribution. In addition to contributing to the literature on school choice, the article illustrates several ways in which distributional effects estimation can enrich educational research: First, we demonstrate that moving beyond a focus on mean effects estimation makes it possible to generate and test new hypotheses about the heterogeneity of educational treatment effects that speak to the justification for many interventions. Second, we demonstrate that distributional effects can uncover issues even with well-studied data sets by forcing analysts to view their data in new ways. Finally, such estimates highlight where in the overall national achievement distribution test scores of children exposed to particular interventions lie; this is important for exploring the external validity of the intervention's effects.     

双模压缩真空态的K次方H压缩效应

本文研究了双模压缩真空态1ξ〉=1/coshr sum from n=0 to(-e~(iθ)tanhr)~n 1n,n)的K次方H压缩效应。数值计算的结果表明:对于双模压缩真空态,光场存在着K次方H压缩效应(K=1,2,3,4,5,Λ);但是,随着方次K的升高,K次方H压缩效应减弱。     

辽东山区的景观变化与景观设计

针对目前辽东山区的基质、斑块和廊道现状，并考虑它的历史演替进程，提出各自的景观设计方案，使之向着更有利于经济持续，生态持续的目标变化。     

楚铜器纹饰的审美特征及其文化内涵

该文着重探讨楚青铜器纹饰发生发展的演变规律、装饰特征 ,阐明其相应的文化背景 ,指出楚铜器纹饰在审美上求奇、求美、花样翻新的价值取向 ,乃是楚民族传统审美心理积淀的结果 ,同时又与当时社会意识形态的变化有关。在楚人独创精神的培育下 ,楚铜器龙纹逐渐演化成为具有楚域风格的装饰纹样。     

论传统文化的消极因素对执政党建设的不良影响

中国传统文化中的优秀精华对我们今天加强党的建设,提高执政能力是有很好的促进作用,但其中的封建专制思想、官本位意识、官僚主义、宗法观念等消极因素以及其他封建没落思想,对当前执政党建设也产生着诸多不良影响。深入剖析这些腐朽思想存在的原因及其危害,可以做到鉴古知今,为加强党的思想作风建设、永葆党的先进性服务。     

聚合氯化铝絮凝剂在电厂水处理中的应用研究

为了提高聚合氯化铝在电厂水处理中的处理效果,以某电厂原水为研究对象,以液体聚合氯化铝为絮凝剂,考察在最佳水力条件下,不同投加量下聚合氯化铝对出水浊度、pH、悬浮物、CODCr等指标的影响情况.研究结果表明,最佳水利参数为:快搅转速200r/min,快搅时间45s,慢搅转速80r/min,慢搅时间15 min;当投加量为12mg/L时,浊度去除率为90.97%,SS去除率可达91.36%,此时出水水质澄清透明.在最佳投加量的确定和保证出水水质的同时,节约了生产成本.     

The Implications of Teacher Selection and the Teacher Effect in Individually Randomized Group Treatment Trials

Abstract

In some experimental evaluations of classroom-level interventions it is not practically feasible to randomly assign teachers to experimental conditions. Given such restrictions, researchers may randomly assign students to experimental conditions and consider the teacher to be a part of the intervention. However, in an individually randomized evaluation of a classroom-level intervention, unless teachers are randomized to experimental conditions, it will not be clear whether differences in outcomes between program and control group students are a result of the core components of the intervention or the teachers (i.e., teacher effects). This article clarifies the correct interpretation of “program impacts” when this study design is used. In addition, using the magnitude of estimated teacher effects from past research, this article demonstrates that, if teachers are not randomly assigned to experimental conditions, it is difficult to establish whether the program works or whether the types of teachers selected to teach in program classrooms are simply more or less effective than their control group counterparts. The significant implications of the correct causal interpretation are discussed, and the limitations of this research design are explored.     

The Long-Term Effects of Small Classes in Early Grades: Lasting Benefits in Mathematics Achievement at Grade 9

Reducing class size to increase academic achievement is a policy option currently of great interest. Although the results of small-scale randomized experiments and some interpretations of large-scale econometric studies point to positive short-term effects of small classes, some scholars view the evidence as ambiguous. Project STAR in Tennessee-a 4-year, large-scale randomized experiment on the effects of class size—provided persuasive evidence that small classes have immediate positive effects on academic achievement. Unlike most other early education interventions, these effects persisted for several years after the children returned to regular-sized classes. The authors of the present article report analyses of a 6-year follow-up of the students in that experiment. Class-size effects persisted for at least 6 years and remained large enough to be important for educational policy. The results suggest that small classes in early grades have lasting benefits and that those benefits are greater for minority students than for White students.     

Modbus Plus网络在电厂水处理控制系统中的应用

介绍MB 网在电厂水处理控制系统中的应用。详细地阐述控制系统的网络结构、软件和硬件设计以及系统能实现的基本功能。     

浅析实验楼供电设计有关问题

提出设计实验楼计算负荷的简便算法,并画出用电系统图;通常不同类型实验室的电气设置;同时也提出了设计中要注意接地问题。     

漳州非遗文化在钟表设计中的开发策略

漳州非物质文化遗产丰富,同时又是中国钟表之城,开发具有漳州非遗文化特色的钟表产品,有利于本土非遗文化的传承发展,促进本土非遗文化和区域经济的协同发展,对助力漳州非遗文化系列钟表品牌的建立具有一定的现实意义。从文化融合和产品开发的角度探讨漳州非遗文化与钟表设计的结合,提出了相应的思路和方法。