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1.
Proportional hazards are a common assumption when designing confirmatory clinical trials in oncology. This assumption not only affects the analysis part but also the sample size calculation. The presence of delayed effects causes a change in the hazard ratio while the trial is ongoing since at the beginning we do not observe any difference between treatment arms, and after some unknown time point, the differences between treatment arms will start to appear. Hence, the proportional hazards assumption no longer holds, and both sample size calculation and analysis methods to be used should be reconsidered. The weighted log‐rank test allows a weighting for early, middle, and late differences through the Fleming and Harrington class of weights and is proven to be more efficient when the proportional hazards assumption does not hold. The Fleming and Harrington class of weights, along with the estimated delay, can be incorporated into the sample size calculation in order to maintain the desired power once the treatment arm differences start to appear. In this article, we explore the impact of delayed effects in group sequential and adaptive group sequential designs and make an empirical evaluation in terms of power and type‐I error rate of the of the weighted log‐rank test in a simulated scenario with fixed values of the Fleming and Harrington class of weights. We also give some practical recommendations regarding which methodology should be used in the presence of delayed effects depending on certain characteristics of the trial. 相似文献
2.
Bioequivalence (BE) studies are designed to show that two formulations of one drug are equivalent and they play an important role in drug development. When in a design stage, it is possible that there is a high degree of uncertainty on variability of the formulations and the actual performance of the test versus reference formulation. Therefore, an interim look may be desirable to stop the study if there is no chance of claiming BE at the end (futility), or claim BE if evidence is sufficient (efficacy), or adjust the sample size. Sequential design approaches specially for BE studies have been proposed previously in publications. We applied modification to the existing methods focusing on simplified multiplicity adjustment and futility stopping. We name our method modified sequential design for BE studies (MSDBE). Simulation results demonstrate comparable performance between MSDBE and the original published methods while MSDBE offers more transparency and better applicability. The R package MSDBE is available at https://sites.google.com/site/modsdbe/ . Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
保建云 《哈尔滨工业大学学报(社会科学版)》2002,4(1):62-66
在一定假设条件下,利用数理经济学方法对区域经济运行中的纯粹交换经济系统、纯粹生产经济系统、生产--交换经济系统中的资源地域空间配置优化进行一般均衡及其均衡扩展比较研究,发现并证明无论何种类型的区域经济体系或多区域经济体系,资源地域空间配置优化的宏观经济效益与微观经济效益并不总是一致的,存在着差异与负相关的可能性. 相似文献
4.
经济运行从开始到达稳定状态一般经过七个阶段。传统劳动价值论认为 ,商品价值由物质生产部门的劳动者在社会生产的第二阶段实际耗费的劳动者支出量加上生产资料转移的价值决定。新价值论认为 ,现代产品价值由产品基本价值、生产资料价值和自然资源价值三部分构成 ,产品基本价值由社会各部门应该耗费的社会必要劳动能力量在生产的前提阶段内在地决定并在第七阶段成为现实。由此决定了传统的价值概念不能包含资源配置和利用。新价值概念本身就蕴涵着资源配置和利用。 相似文献
5.
基于复杂适应系统的作战理论哲学反思 总被引:1,自引:0,他引:1
传统的作战理论与方法已经不能适应像现代信息化战争系统这类充满“活”的个体和变化因素的复杂系统,需要进行理论创新。而复杂适应系统理论是当代系统科学的一个新发展。有望成为创新作战理论的突破口。本文在分析比较作战系统的基础上,认为作战系统实质是复杂的适应系统,作战系统内的作战双方都力图以增强自身的适应性和复杂性,削弱对方的适应性和复杂性取得作战的胜利。 相似文献
6.
多校区图书馆的典藏工作 总被引:8,自引:0,他引:8
孙玉鹏 《江苏科技大学学报(自然科学版)》2003,3(3):74-75
高校合并后,许多院校的图书馆都出现了多校区、多分馆的管理局面。笔者从新图书典藏、调拨、剔除几个方面简要论述了如何搞好多校区图书馆的典藏工作。 相似文献
7.
描述了影响DBF系统特性的主要因素,研究了阵元间互耦对自适应方向图旁瓣和零深的影响及校正方法,讨论了在DBF阵中校正接收通道幅、相误差和I/Q支路正交误差的技术途径。计算机模拟和测试证明,按照所述方法进行校正可以得到满意的结果。另外,为了减小I/Q支路产生正交误差,建议采用中频直接采样和数字化的接收机方案。 相似文献
8.
Angelo Zanella 《Statistical Methods and Applications》1992,1(1):143-160
Summary For technological applications it can be useful to identify some simple physical mechanisms, which, on the basis of the available
knowledge of the production process, may suggest the most appropriate approach to statistical control of the random quantities
of interest. For this purpose the notion of rupture point is introduced firstly. A rupture point is characterized bym randomly arising out of control states, assumed to be mutually exclusive and stochastically independent. Shewhart's control
charts seem to represent the natural statistical tool for controlling a rupture point; however it is shown that they are fully
justified only when the hazard rates attached to the causes of failure are constant. Otherwise, typically in the presence
of time increasing hazard rates, Shewhart's control charts should be completed by a preventive intervention rule (preventive
maintenance). In the second place, the notion of dynamic instability point is introduced, which is specifically characterized
by assuming that the random quantity of interest is ruled by a stochastic differential equation with constant coefficients.
By discretization, developed according to a possibly new approach, it is shown that the former model reduces to an equation
error model, which is among the simplest used in adaptive control, and thus particularly easy to deal with in regard to parameter
estimation and the definition of the optimum control rule. 相似文献
9.
学术期刊属性研究 总被引:3,自引:0,他引:3
尹玉吉 《山东理工大学学报(社会科学版)》2006,22(2):99-105
在编辑传播学界关于学术期刊属性的研究上,普遍存在着一个突出的问题,这就是论者们几乎不假思索地认为“学术期刊是商品”。我们认为,这是一个很大的误区,这种认识在理论上是错误的,在实践上是有害的。首先,“学术期刊商品论”是自相矛盾的;其次,“学术期刊商品论”与马克思主义经济学是相悖的;再次,“学术期刊商品论”与普遍存在的事实是恰恰相反的。学术期刊和学术事业是一项创新的事业,它关系一个国家的生存安危,对此,江泽民同志曾经反复强调,创新是一个民族进步的灵魂,是国家兴旺发达的不竭动力之源。因此,对待学术和学术期刊事业应当像对待军队、警察机构一样,不能也不可能使其商品化,学术期刊应该走自己的健康发展之路。 相似文献
10.
Hunter LM 《Population research and policy review》2006,25(2):157-174
In many developing regions, women and young girls spend several hours daily in the collection of natural resources. Still the link between these household resource strategies and stakeholder perceptions of development priorities remains unexplored. This project examines this association with survey data representative of the adult population from Ghana’s Coastal Region. Although natural resource scarcity and the sustainability of resource use represent key development challenges, there are others (e.g., energy, sanitation, employment, and educational opportunities). As such, even in the face of natural resource scarcity, individuals may place greater importance on other dimensions of development, especially if household resource strategies are perceived as relatively efficient. The analytical focus here is on water and the results suggest that gender roles shape household water collection strategies, while also shaping these strategies’ perceived opportunity costs. Specifically, Ghanian adults more often see drinking water provision as their primary development need when water sources are distant and/or when male household members collect water (particularly male heads). In the end, I argue that social science inquiry benefits by contextualizing social dynamics within environmental context, particularly within cultural settings in which human subsistence is intimately tied to the state of the natural environment. 相似文献