共查询到20条相似文献，搜索用时 31 毫秒
1.
AbstractWhen well-implemented, mediation analyses play a critical role in probing theories of action because their results help lay the ground work for the critical development of a treatment and the iterative advancement of theories that are foundational to a discipline. Despite strong interest in designs that incorporate mediation, few studies have developed effective and efficient strategies to plan experiments examining multilevel mediation. We probe several design strategies for cluster-randomized designs and derive sampling plans that maximize power under cost constraints. The results suggest that among the more durable design strategies for mediation is covariance adjustment on variables predictive of the outcome and optimal sample allocation. The statistical power and optimal sample allocation results are implemented in the R package PowerUpR. 相似文献
2.
An important concern when planning research studies is to obtain maximum precision of an estimate of a treatment effect given a budget constraint. When research designs have a multilevel or hierarchical structure changes in sample size at different levels of the design will impact precision differently. Furthermore, there will typically be differential costs of enrolling additional units at different levels of the hierarchy. The optimal design problem in multilevel research studies involves determining the optimal sample size at each level of the design given specified design parameters and a specified marginal cost of recruitment at each level. The current work extends existing results by considering optimal design for (a) unbalanced random assignment designs and (b) regression discontinuity designs. 相似文献
3.
This article discusses the sample size requirements for the interaction, row, and column effects, respectively, by forming a linear contrast for a 2×2 factorial design for fixed-effects heterogeneous analysis of variance. The proposed method uses the Welch t test and its corresponding degrees of freedom to calculate the final sample size in a 2-step procedure. The simulation results show that the proposed sample size allocation ratio can minimize the sampling cost, while at the same time the designated power is achieved. The article concludes with a discussion to reiterate the importance of sample size planning, especially for testing the iteration effect. 相似文献
4.
HAN Shu-guang JIANG Yi-wei HU Jue-liang 《浙江大学学报(A卷英文版)》2007,8(1):127-133
INTRODUCTION In this paper we investigate the uniform ma-chines scheduling problem with machine activationcost. This problem has application in garment pro-duction of international trade and is motivated by thefollowing scenario. Import-export company is com-pared to scheduler in this model, and orders are jobs,which arrive one by one. And garment factories canbe regarded as machines. Since jobs should be fin-ished on time, scheduler will choose a reasonablenumber of machines to make the… 相似文献
5.
The asymptotically distribution free (ADF) method is often used to estimate parameters or test models without a normal distribution assumption on variables, both in covariance structure analysis and in correlation structure analysis. However, little has been done to study the differences in behaviors of the ADF method in covariance versus correlation structure analysis. The behaviors of 3 test statistics frequently used to evaluate structural equation models with nonnormally distributed variables, χ2 test TAGLS and its small-sample variants TYB and TF(AGLS) were compared. Results showed that the ADF method in correlation structure analysis with test statistic TAGLS performs much better at small sample sizes than the corresponding test for covariance structures. In contrast, test statistics TYB and TF(AGLS) under the same conditions generally perform better with covariance structures than with correlation structures. It is proposed that excessively large and variable condition numbers of weight matrices are a cause of poor behavior of ADF test statistics in small samples, and results showed that these condition numbers are systematically increased with substantial increase in variance as sample size decreases. Implications for research and practice are discussed. 相似文献
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The effectiveness of various analytical formulas for estimating R 2 shrinkage in multiple regression analysis was investigated. Two categories of formulas were identified: estimators of the squared population multiple correlation coefficient (ρ2) and those of the squared population cross-validity coefficient (ρc 2). The authors conducted a Monte Carlo experiment to investigate the effectiveness of the analytical formulas for estimating R 2 shrinkage, with 4 fully crossed factors (squared population multiple correlation coefficient, number of predictors, sample size, and degree of multicollinearity) and 500 replications in each cell. The results indicated that the most widely used Wherry formula (in both SAS and SPSS) is probably not the most effective analytical formula for estimating ρ2. Instead, the Pratt formula and the Browne formula outperformed other analytical formulas in estimating ρ2 and ρc 2, respectively. 相似文献
7.
高校教室资源优化配置研究 总被引：2，自引：0，他引：2
教室资源配置的难点由来已久,然而在实际教学管理过程中,往往得不到应有的重视,而且随着高等教育的发展,这方面问题的发展已经蕴涵了新的特点、要求,也要求高等教育的具体管理者给以更多的关注。从当前宏观和微观的背景着手,分析高校教室资源优化配置的内容,并从高校教室的管理主体、构成结构及日常使用管理等三方面分析高校教室资源优化配置的途径。 相似文献
8.
Fitting a large structural equation modeling (SEM) model with moderate to small sample sizes results in an inflated Type I error rate for the likelihood ratio test statistic under the chi-square reference distribution, known as the model size effect. In this article, we show that the number of observed variables (p) and the number of free parameters (q) have unique effects on the Type I error rate of the likelihood ratio test statistic. In addition, the effects of p and q cannot be fully explained using degrees of freedom (df). We also evaluated the performance of 4 correctional methods for the model size effect, including Bartlett’s (1950), Swain’s (1975), and Yuan’s (2005) corrected statistics, and Yuan, Tian, and Yanagihara’s (2015) empirically corrected statistic. We found that Yuan et al.’s (2015) empirically corrected statistic generally yields the best performance in controlling the Type I error rate when fitting large SEM models. 相似文献
9.
SHE Feng LUO Han-wen WANG Xin 《浙江大学学报(A卷英文版)》2007,8(12):1894-1900
This paper deals with the design and performance analysis of the transmission precoder optimization for multiple-input multiple-output (MIMO) systems with limited feedback of channel state information (CSI). We assume that the receiver can get perfect channel knowledge by channel estimation while the transmitter only has partial channel knowledge from limited feedback. We present a minimum mean square error (MMSE) criterion based codebook construction algorithm for MIMO pre- coded spatial multiplexing systems under a specific average power constraint. The optimal transmitter structure is employed in this paper. Simulation results show that the MMSE criteria based codebook construction algorithm with hybrid design of power allocation and precoding can achieve better performance than that of equal power allocation based codebook of previous research. 相似文献
10.
AbstractInvestment of time in internship and in-school learning or study are two ways to accumulate human capital for college students. The authors take I&S input as two impacting faAQctors for graduates’ starting salaries to construct an I&S input allocation model minimizing “psychological cost.” The model inference indicates that the optimal allocation of I&S input relies on three aspects: returns to I&S of the future labor market, graduates’ cognitive attitudes toward the role of I&S, and the comparative advantages of I&S. The authors use the 2015 China College Graduates’ Employment Survey data conducted by the Institute of Education at Peking University to empirically verify the theoretical model. They found that under the current labor market conditions, the time input on I&S does not necessarily bring better returns, and there is a significant difference among student groups between the actual I&S time input and the “theoretically optimal values” predicted by the model. The authors conclude that the failure of allocating the I&S time input will hinder graduates’ successful transition from universities to the labor market. To avoid this time input imbalance, institutions should strengthen the guidance of I&S time input, improve the related management system, and pay more attention to I&S input quality and optimal allocation. 相似文献
11.
Esther Ulitzsch Jana Holtmann Martin Schultze Michael Eid 《Structural equation modeling》2017,24(1):80-103
This simulation study assesses the statistical performance of two mathematically equivalent parameterizations for multitrait–multimethod data with interchangeable raters—a multilevel confirmatory factor analysis (CFA) and a classical CFA parameterization. The sample sizes of targets and raters, the factorial structure of the trait factors, and rater missingness are varied. The classical CFA approach yields a high proportion of improper solutions under conditions with small sample sizes and indicator-specific trait factors. In general, trait factor related parameters are more sensitive to bias than other types of parameters. For multilevel CFAs, there is a drastic bias in fit statistics under conditions with unidimensional trait factors on the between level, where root mean square error of approximation (RMSEA) and χ2 distributions reveal a downward bias, whereas the between standardized root mean square residual is biased upwards. In contrast, RMSEA and χ2 for classical CFA models are severely upwardly biased in conditions with a high number of raters and a small number of targets. 相似文献
12.
曹令秋 《株洲师范高等专科学校学报》2007,12(5):30-31
构建了一个两部门一般性社会计划者的最优决策随机模型，运用随机分析方法．分析了不确定条件下社会计划者关于消费和资本配置的最优决策． 相似文献
13.
采用鲁棒区间算法解决目标函数和约束条件中的不确定性问题,开发一个鲁棒区间能源系统规划模型,通过求解得到模型全局最优解,以获得最小的能源成本及最优的能源分配方案．案例研究结果显示。通过此优化模型进行的综合环境约束的规划,能使城市能源消费整体结构得到优化,能源利用效率明显提高,可实现城市的能源经济环境的协调发展． 相似文献
14.
INTRODUCTION With the development of novel wireless tech- nologies and increasing available bandwidth, multi- media applications over wireless networks become attractive for both businesses and end users. Fast de- ployment of Wi-Fi HotSpots, increase in wireless coverage of remote habitable areas (Wi-Max, or wireless mesh networks), improved data services over the 2G cellular systems and the long awaited debut of 3G wireless services offer many potential and inter- operable communicatio… 相似文献
15.
苗敬毅 《山西财经大学学报(高等教育版)》2010,13(3):88-91
在分析影响煤炭资源优化配置主要因素的基础上,从可持续发展、新型工业化、产业安全、循环经济、资源监控五个方面提出了煤炭资源优化配置评价指标体系,从而为煤炭资源优化配置的定量评价奠定了基础。 相似文献
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分析了医院医疗服务成本的核算与管理,提出基于B/S三层3-tier架构,采用Tomact6.0＋JSP2.0开发和配置应用层的JSP服务器以及SQL SERVER 2000数据库,使用四级分摊理论和本量利分析法,研究开发医院成本核算系统.该系统能够准确及时地计算医院的成本费用和消耗,实现了医院成本结构的优化调整,达到了成本的有效控制. 相似文献
18.
A novel simplified method is presented to design FIR filter with controllable center frequency. The properties of transfer curves for all-phase filters are illustrated under 3 windowing conditions. By combining single-window all-phase filter design steps and double phase-shift combination, a series of design formulas for point-pass filter, notch filter, band-pass filter and band-stop filter are derived, thus the design computation complexity is greatly reduced. Experiments prove that the center frequency of all the filters can be accurately specified at arbitrary position by adjusting frequency parameters m and λ. 相似文献
19.
The authors defined optimal experience as a functional state of a relatively high level of concentration, time distortion, satisfaction, and enjoyment (Csikszentmihalyi, 1992) and collected data through the Day Reconstruction Method. In three random days, 147 fifth-grade students answered questionnaires for each school event in the previous day resulting repeated data from 2,288 episodes. Several hierarchical linear models were conducted. The authors found that elementary students perceived better quality of optimal experience during break time versus classes taught by activity, seatwork or lecture methods. Unexpectedly, more optimal experience was reported in the events when students perceived themselves as having high skill but low challenge, contradictory to the original expectation of skill–challenge balance. Four additional flow conditions were more effective than primary flow condition and instructional methods in predicting optimal experience. Finally, optimal experience varied much more across event-episodes than among individuals meaning that teachers have rooms to improve students' optimal experience in elementary school days. 相似文献
20.
《Journal of research on educational effectiveness》2013,6(3):263-294
Abstract This article develops a new approach for calculating appropriate sample sizes for school-based randomized control trials (RCTs) with binary outcomes using logit models with and without baseline covariates. The theoretical analysis develops sample size formulas for clustered designs where random assignment is at the school or teacher level using generalized estimating equation methods. The article focuses on the impact parameter pertaining to rates and proportions rather than to the log odds of response, which has been the focus of the previous literature. The article also compiles intraclass correlations (ICCs) for the clustered design for a range of binary outcomes using data from seven education RCTs. These ICCs and the power formulas are then used to conduct a power analysis using a provided SAS macro; the key finding is that sample sizes of 40 to 60 schools that are typically included in clustered RCTs for student test score or behavioral scale outcomes will often be insufficient for binary outcomes. A key reason is that the potential for precision gains from regression adjustment is likely to be smaller for binary outcomes. 相似文献