Sample size and power calculations based on generalized linear mixed models with correlated binary outcomes

The generalized linear mixed model (GLIMMIX) provides a powerful technique to model correlated outcomes with different types of distributions. The model can now be easily implemented with SAS PROC GLIMMIX in version 9.1. For binary outcomes, linearization methods of penalized quasi-likelihood (PQL) or marginal quasi-likelihood (MQL) provide relatively accurate variance estimates for fixed effects. Using GLIMMIX based on these linearization methods, we derived formulas for power and sample size calculations for longitudinal designs with attrition over time. We found that the power and sample size estimates depend on the within-subject correlation and the size of random effects. In this article, we present tables of minimum sample sizes commonly used to test hypotheses for longitudinal studies. A simulation study was used to compare the results. We also provide a Web link to the SAS macro that we developed to compute power and sample sizes for correlated binary outcomes.     

Sample size calculations for a functional human motion analysis: Application to vehicle ingress discomfort prediction

The ease of entering a vehicle, known as ingress, is one of the important ergonomic factors that car manufacturers consider during the process of vehicle design. Manufacturers frequently conduct human subject tests to assess ingress discomfort for different vehicle designs. Using subject tests, manufacturers are able to estimate the proportion of participants that report that they are discomfortable entering a vehicle, referred to in this paper as fraction disaccommodated (FD). Manufacturers then conduct statistical tests in order to determine if the FD of two vehicle designs are significantly different, and to determine the required sample size in testing the FD difference between two vehicle designs under pre-specified testing power. Since conducting human subject tests is often expensive and time consuming, another alternative is to estimate the FD using simulated human motion data. Determining the number of simulations that is required is an important statistical question that is dependent on the prediction performance of the simulation analysis. In this paper, a dual bootstrap approach is proposed to obtain the standard deviation of the estimated FD based on functional predictors. This standard deviation is then used to calculate the power in testing the difference between two estimated FDs.     

Sample size calculation for non-compliance randomized trials with repeated measurements in binary data

When we have difficulty in recruiting patients into a randomized clinical trial (RCT), we may consider taking more than one measurement per patient to reduce the number of patients needed to achieve a desired power. In this paper, we consider a double blind RCT with two courses of treatment per patient. At each course, a patient assigned to the experimental treatment could switch to receive the placebo if the patient declined his/her assigned (experimental) treatment, and a patient assigned to the placebo could switch to receive the experimental treatment if the patient refused his/her assigned (placebo) treatment as well. Sample size calculation without accounting for this non-compliance can be inadequate when we apply the standard procedure of intention-to-treat analysis for non-compliance trials to test no treatment effect. Based on the simple additive risk model proposed elsewhere, we have incorporated the initial probability of compliance, the dependence of patient's selection of a treatment on his/her previous response, and the variation of probabilities of response between patients into sample size determination. We have included a quantitative discussion that provides an insight into the effect of various parameters on the minimum required sample size. We have also noted the situation in which taking repeated measurements per patient can be most effective to reduce the number of patients needed to maintain a given power.     

Sample size and class variability in the choice of a method of discriminant analysis

The choice between linear and quadratic discriminant analysis in a simulation, (where DN values are normally distributed within classes and the classes are of known prior probability), is shown to depend on the size of the training sample and the extent to which the within-class variance-covariance matrices difTer from each other.     

射频/微波功率测量不确定度分析及计算

本文根据戴维宁等效电路,建立了射频,微波功率传输信号流图,阐述了功率测量电路中相关测量参数及其相互关系,并分析了测量不确定度的来源及改善失配误差的方法,最后介绍了常见的三种测量不确定合成方法:最大误差不确定度、RSS误差不确定度和扩展不确定度.     

Computerized mouse pupil size measurement for pupillary light reflex analysis

Accurate measurement of pupil size is essential for pupillary light reflex (PLR) analysis in clinical diagnosis and vision research. Low pupil–iris contrast, corneal reflection, artifacts and noises in infrared eye imaging pose challenges for automated pupil detection and measurement. This paper describes a computerized method for pupil detection or identification. After segmentation by a region-growing algorithm, pupils are detected by an iterative randomized Hough transform (IRHT) with an elliptical model. The IRHT iteratively suppresses the effects of extraneous structures and noise, yielding reliable measurements. Experimental results with 72 images showed a mean absolute difference of 3.84% between computerized and manual measurements. The inter-run variation for the computerized method (1.24%) was much smaller than the inter-observer variation for the manual method (7.45%), suggesting a higher level of consistency of the former. The computerized method could facilitate PLR analysis and other non-invasive functional tests that require pupil size measurements.     

Code size reduction by compressing repeated instruction sequences

This paper presents an efficient technique for code compression. In our work, a sequence of instructions that occurs repeatedly in an application will be compressed to reduce its code size. During compression, each instruction is first divided into the operation part and the register part, and then only the operation part is compressed. The compression information is stored in the instruction table, the register bank, and the index table. For reducing the run-time overhead, we propose an instruction prefetching mechanism to speed the decompression. Our work is performed with SPEC 2000, DSPstone, Mediabench, and MPEG4 benchmarks on the basis of the ARM instruction set. It is proved to be quite effective for media and other applications. The experimental results show that our work can achieve a code size reduction of 33% on average and a low overhead in the process of decompression at run time for these benchmarks.     

Sample size computation for designing multiple comparison experiments

This article considers sample size computation for designing multiple comparisons experiments. We propose sample size should be computed so that multiple comparisons confidence intervals will cover the true parameters and be sufficiently narrow with a guaranteed high probability. Appropriate formulas and computer implementation are provided for Tukey's method of all-pairwise multiple comparisons (MCA), multiple comparisons with the best (MCB) as proposed by the author, and Dunnett's method of multiple comparisons with a control (MCC). Our sample size computation is then compared with the usual computation based on the power of the F-test. An advantage of our method over the usual power-of-test method is that our method guarantees a high probability of correct multiple comparisons inference, while the latter does not, because the probability of rejecting a false null hypothesis includes the probability of directional error (inferring a treatment to be better than another when it is in fact worse). The graphical nature of our computer implementation also makes sensitivity analysis immediate.     

多用户电能计量管理系统

介绍了根据学生公窝用电负荷特点而研制开发的多用户电能计量控制系统的基本结构及实现方法.系统采用主从式结构,上位机对用户的用电信息进行读写、汇总和管理;下位机采用单片机系统对电量数据进行采集、计量和对用户负载进行监控,由电量采集模块、数据处理/控制模块、显示模块等组成.该系统能够实现用电管理的自动化与智能化,而且计量精度高,工作可靠.     

避免数据包重复采集的分布式流量测量算法

针对D PC算法存在的问题,提出一种“标记”数据包头的分布式流量测量算法。为避免同一数据包被不同测量点重复采集,在网络入口测量点处,对到达的数据包进行抽样,修改被抽取数据包头中标志位的预留位为1;在网络的中间节点,通过查看数据包的预留位判断数据包是否已被抽取,对于已被抽取的数据包,不再重复记录,对于尚未被抽取的数据包,根据抽样规则决定是否抽取,避免多次采集相同数据包导致计算资源和存储资源的重复消耗。通过理论推导和实例验证了该算法的有效性,为分布式网络流量测量的扩展应用提供了解决途径。     

Efficient procedures for repeated calculations of the structural response using combined approximations

Efficient procedures for repeated calculations of the response of large-scale structures that involve numerous repeated analyses are presented. These procedures are based on the combined approximations approach, which is further developed to improve both the efficiency of the calculations and the accuracy of the results. The procedures are suitable for linear, nonlinear, static, and dynamic reanalysis problems, and they can be used to improve the efficiency of response surface calculations. It is shown that the procedures presented provide accurate approximations and may significantly reduce the computational effort involved in reanalysis of large-scale structures. This might prove useful in various design and optimization problems.     

Sample size and dimensionality in multivariate classification: implications for body surface potential mapping

This paper presents empirically determined guidelines for specifying the number of features appropriate for multivariate classification studies for given sample sizes. Sample size was considered adequate if the mean distance between two sample sets, taken from the same continuous multivariate distribution and projected onto the best separating direction, remained below a prescribed level. To quantitate the sample size requirement, homogeneity of sample set pairs of equal size. N, taken from the same continuous multivariate distribution was studied as a function of dimensionality. M. Homogeneity was characterized by the maximum absolute distances (Dmax) between the corresponding pairs of empirical cumulative probability distributions on the best separating projection. Computer generated data sets were used to estimate the cumulative probability distribution, P(D)M.N, for sample sizes, N, ranging from 5 to 100 and the dimensionality, M, ranging from 1 to 4. An empirical relationship between the estimated step-polygons and the Kolmogorov type one dimensional limiting distribution L(z) has been established. Based on the sample size data of 34 key papers on clinical body surface potential mapping (BSPM) it is noted that in 30% of the cases only one, and in 6% of the cases only two parameters could be used for statistical group representation to ensure a reasonable reliability (Dmax less than 0.2). In 56% of the published cases the sample sizes could not guarantee this reliability even for one feature or parameter.     

M310核电机组影响蒸汽发生器液位测量通道的因素分析

根据蒸汽发生器（sG）液位测量系统的工作原理和现状,结合检修、运行积累的经验和数据,对影响液位测量通道的因素进行分析及计算,重点剖析了四个窄量程液位变送器在不同功率平台出现指示偏差较大的异常情况及原因,提出了相应的处理意见,以期达到能改善仪表工作现状,减少蒸汽发生器水位控制波动造成严重后果的机率。     

一种通用的软件功能规模度量模型

功能规模度量（FSM）方法通过量化用户功能需求(FUR)而得到软件功能规模。针对不同的功能规模度量方法都是使用不同的抽象来描述一个软件系统的问题,提出了一种通用的FSM模型。根据软件系统的抽象模型,首先对度量所涉及的数据组和事务进行了泛化,然后以IFPUG FPA为例详细说明了该通用模型和FPA之间的转换过程,最后给出了度量过程的算法描述。     

Software productivity measurement using multiple size measures

Productivity measures based on a simple ratio of product size to project effort assume that size can be determined as a single measure. If there are many possible size measures in a data set and no obvious model for aggregating the measures into a single measure, we propose using the expression AdjustedSize/Effort to measure productivity. AdjustedSize is defined as the most appropriate regression-based effort estimation model, where all the size measures selected for inclusion in the estimation model have a regression parameter significantly different from zero (p<0.05). This productivity measurement method ensures that each project has an expected productivity value of one. Values between zero and one indicate lower than expected productivity, values greater than one indicate higher than expected productivity. We discuss the assumptions underlying this productivity measurement method and present an example of its use for Web application projects. We also explain the relationship between effort prediction models and productivity models.     

A vector-based approach to software size measurement and effortestimation

Software size is a fundamental product measure that can be used for assessment, prediction and improvement purposes. However, existing software size measures, such as function points, do not address the underlying problem complexity of software systems adequately. This can result in disproportional measures of software size for different types of systems. We propose a vector size measure (VSM) that incorporates both functionality and problem complexity in a balanced and orthogonal manner. The VSM is used as the input to a vector prediction model (VPM) which can be used to estimate development effort early in the software life-cycle. We theoretically validate the approach against a formal framework. We also empirically validate the approach with a pilot study. The results indicate that the approach provides a mechanism to measure the size of software systems, classify software systems, and estimate development effort early in the software life-cycle to within ±20% across a range of application types     

三相电气参量快速和高精度的测量算法

提出了一种快速富里叶变换FFT算法来测量电力系统基波频率和其它谐波频率的实时值,进而计算出三相电压和电流的有效值与相位的实际值。由于电力系统参数随时都在变化,非正弦信号的系统基波频率不可能是一个确定的值,采用未确定的系统基波频率来采样和测量非正弦信号变化的三相电压和电流将引起很大的误差。因此,提出先准确测量非正弦信号的系统基波频率,然后,采用准确的系统基波频率来采样三相电压和电流,进而再计算三相电压和电流的有效值与相位的实际值、有功功率与电能、无功功率与电能等。这种算法不仅大大缩短计算时间,而且提高了测量的精度,测量精度可以达到0.1%或更高。实例计算的仿真结果及实际应用系统的运行数据都证明:这种算法的可靠性、准确性和快速性。     

Rethinking organisational size in IS research: meaning,measurement and redevelopment

While organisational size is a popular construct in information systems (IS) research, findings from its use have been inconsistent. Few studies have explored this inconsistency or attempted to address this problem. This paper uses Churchill's measure development paradigm to conduct three separate but related investigations into the size construct. Study 1 explored the domain and dimensions of size. Some 2000 research papers published in six leading IS journals over an 11-year period were read in order to determine what researchers thought size meant and how they measured it. The study found 21 constructs underpinning the size construct and 25 ways of measuring size, but no clear relationship between size meaning and measurement. Study 2 assessed the construct's content validity using a concept map exercise involving 41 participants. Multidimensional scaling clustered the constructs into three conceptual groups. Study 3 administered the size construct in a survey with a sample of 163 Australian firms. The study found that the data supported the constructs observed in Study 2 and that a group of eight constructs could be used to differentiate between smaller and larger firms in the sample. Analysis revealed that organisational levels, risk aversion, geographic distribution and employment reflected respondents’ self-nominated size.     

激光粒度测量中扇形SSPD的数据采集与处理

根据扇形自扫描光电二极管阵列 -SSPD的工作原理及信号特点 ,提出了一种计算机控制的数据采集与处理方法 ,包括串行微弱信号的放大、时序的配合、微机接口电路及非线性修正等内容 ,可以以较高的精度实时采集到SSPD各环的峰值。可应用于激光粒度的测量与其它空间光能量分布的探测中