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91.
Phillip Dinh 《Pharmaceutical statistics》2013,12(5):260-267
In longitudinal clinical studies, after randomization at baseline, subjects are followed for a period of time for development of symptoms. The interested inference could be the mean change from baseline to a particular visit in some lab values, the proportion of responders to some threshold category at a particular visit post baseline, or the time to some important event. However, in some applications, the interest may be in estimating the cumulative distribution function (CDF) at a fixed time point post baseline. When the data are fully observed, the CDF can be estimated by the empirical CDF. When patients discontinue prematurely during the course of the study, the empirical CDF cannot be directly used. In this paper, we use multiple imputation as a way to estimate the CDF in longitudinal studies when data are missing at random. The validity of the method is assessed on the basis of the bias and the Kolmogorov–Smirnov distance. The results suggest that multiple imputation yields less bias and less variability than the often used last observation carried forward method. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
92.
Prior studies in the sociology of accidents have shown that different social groups have different rates of accident involvement. This study extends those studies by implementing Bourdieu's relational perspective of social space to systematically explore the homology between drivers’ social characteristics and their involvement in specific types of motor vehicle accident. Using a large database that merges official Israeli road‐accident records with socioeconomic data from two censuses, this research maps the social order of road accidents through multiple correspondence analysis. Extending prior studies, the results show that different social groups indeed tend to be involved in motor vehicle accidents of different types and severity. For example, we find that drivers from low socioeconomic backgrounds are overinvolved in severe accidents with fatal outcomes. The new findings reported here shed light on the social regularity of road accidents and expose new facets in the social organization of death. 相似文献
93.
马达海洋工区海底深度变化很大,多次波异常发育,多次波衰减一直是该区地震资料处理难题之一。首先分
析与自由表面相关多次波衰减方法(SRME)、预测反褶积、抛物线Radon 变换的方法原理,针对各方法的不同特点制
定方案:采用SRME 方法衰减与自由表面相关的多次波,预测反褶积方法压制层间多次波,抛物线Radon 变换法衰减
剩余的多次波。实际资料处理表明:这种分步分段压制多次波的方法能够很好地衰减海底深度变化范围大、海底构造
复杂的海洋地震资料的多次波,很好地改善海洋地震资料的成像效果。实际资料处理表明,这种分段压制多次波方法
能够广泛应用于海底深度变化大,海底地质构造复杂的海洋地震资料多次波衰减处理。 相似文献
94.
Imputation methods that assign a selection of respondents’ values for missing i tern nonresponses give rise to an addd,tional source of sampling variation, which we term imputation varLance , We examine the effect of imputation variance on the precision of the mean, and propose four procedures for sampling the rEespondents that reduce this additional variance. Two of the procedures employ improved sample designs through selection of respc,ndents by sampling without replacement and by stratified sampl;lng. The other two increase the sample base by the use of multiple imputations. 相似文献
95.
《Journal of child sexual abuse》2013,22(2):25-40
ABSTRACTRecovering substance abusers with a history of childhood sexual abuse (n = 69) or no history of childhood sexual abuse (n = 68) completed the Toronto Alexithymia Scale (TAS) and a background survey assessing demographic data and (In the case of sexually abused respondents) parameters of the childhood abuse experienced. The sexually abused group scored significantly higher than the non-abused group on the TAS. Within the abused group, measured alexithymic symptomatology was found to be related positively to the duration of the abuse. Alexithymia was significantly higher when the sexual abuse first occurred after the victim had reached the age of 12, when a perpetrator of the sexual abuse was a father or stepfather, and when the abuse involved oral, vaginal, and/or anal penetration. Results were interpreted as indicating that the development of alexithymic symptoms may represent another defense victims may employ to insulate themselves from painful affect, along with dissociative symptoms and substance abuse, which have been shown previously to characterize adult survivors of child sexual abuse. 相似文献
96.
Bruce Levin 《统计学通讯:理论与方法》2013,42(11):1299-1327
We describe a method of computing the cumulative distribution function of the maximum and minimum cell frequencies in sampling distributions commonly encountered in the analysis of categorical data.The procedure is efficient for exact or approximate calculation in both homogeneous and non-homogeneous cases, is non-recursive, and does not require Dirichlet integrals.Some related statistical problems are also discussed. 相似文献
97.
Eric Specking Bobby Cottam Gregory Parnell Edward Pohl Matthew Cilli Randy Buchanan Zephan Wade Colin Small 《Risk analysis》2019,39(9):1899-1912
Recently, efforts to model and assess a system's resilience to disruptions due to environmental and adversarial threats have increased substantially. Researchers have investigated resilience in many disciplines, including sociology, psychology, computer networks, and engineering systems, to name a few. When assessing engineering system resilience, the resilience assessment typically considers a single performance measure, a disruption, a loss of performance, the time required to recover, or a combination of these elements. We define and use a resilient engineered system definition that separates system resilience into platform and mission resilience. Most complex systems have multiple performance measures; this research proposes using multiple objective decision analysis to assess system resilience for systems with multiple performance measures using two distinct methods. The first method quantifies platform resilience and includes resilience and other “ilities” directly in the value hierarchy, while the second method quantifies mission resilience and uses the “ilities” in the calculation of the expected mission performance for every performance measure in the value hierarchy. We illustrate the mission resilience method using a transportation systems‐of‐systems network with varying levels of resilience due to the level of connectivity and autonomy of the vehicles and platform resilience by using a notional military example. Our analysis found that it is necessary to quantify performance in context with specific mission(s) and scenario(s) under specific threat(s) and then use modeling and simulation to help determine the resilience of a system for a given set of conditions. The example demonstrates how incorporating system mission resilience can improve performance for some performance measures while negatively affecting others. 相似文献
98.
我国企业多元化投资决策的反思 总被引:1,自引:0,他引:1
周渊 《重庆工商大学学报(社会科学版)》2002,19(1):41-43
企业多元化经营战备是当今世界许多大中型企业的一种战备选择。我国的一些大企业近年来也走上了多元化经营的道路 ,但多数都身陷困境或遭受失败 ,主要是由于多元化投资决策失误所致。因此 ,深入探讨多元化投资的理论和战略 ,对我国一些大中型企业来说 ,就显得十分重要。 相似文献
99.
职业伴随着劳动分工而产生,职业教育则是近代大机器工业的产物。在不同的历史时期,人们从不同的角度观察,并对职业教育产生了不同的认识,以不同的名称表述,赋予不同的功能。"五四"时期职业教育的多元共生,反映出人们对职业教育概念、功能的不同认识,这也是中国近代职业教育向现代职业教育跨越的重要标志。 相似文献
100.
Recurrent events are frequently observed in biomedical studies, and often more than one type of event is of interest. Follow-up time may be censored due to loss to follow-up or administrative censoring. We propose a class of semi-parametric marginal means/rates models, with a general relative risk form, for assessing the effect of covariates on the censored event processes of interest. We formulate estimating equations for the model parameters, and examine asymptotic properties of the parameter estimators. Finite sample properties of the regression coefficients are examined through simulations. The proposed methods are applied to a retrospective cohort study of risk factors for preschool asthma. 相似文献