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1.
In the quest to model various phenomena, the foundational importance of parameter identifiability to sound statistical modeling may be less well appreciated than goodness of fit. Identifiability concerns the quality of objective information in data to facilitate estimation of a parameter, while nonidentifiability means there are parameters in a model about which the data provide little or no information. In purely empirical models where parsimonious good fit is the chief concern, nonidentifiability (or parameter redundancy) implies overparameterization of the model. In contrast, nonidentifiability implies underinformativeness of available data in mechanistically derived models where parameters are interpreted as having strong practical meaning. This study explores illustrative examples of structural nonidentifiability and its implications using mechanistically derived models (for repeated presence/absence analyses and dose–response of Escherichia coli O157:H7 and norovirus) drawn from quantitative microbial risk assessment. Following algebraic proof of nonidentifiability in these examples, profile likelihood analysis and Bayesian Markov Chain Monte Carlo with uniform priors are illustrated as tools to help detect model parameters that are not strongly identifiable. It is shown that identifiability should be considered during experimental design and ethics approval to ensure generated data can yield strong objective information about all mechanistic parameters of interest. When Bayesian methods are applied to a nonidentifiable model, the subjective prior effectively fabricates information about any parameters about which the data carry no objective information. Finally, structural nonidentifiability can lead to spurious models that fit data well but can yield severely flawed inferences and predictions when they are interpreted or used inappropriately.  相似文献   
2.
In this paper, we propose a novel Max-Relevance and Min-Common-Redundancy criterion for variable selection in linear models. Considering that the ensemble approach for variable selection has been proven to be quite effective in linear regression models, we construct a variable selection ensemble (VSE) by combining the presented stochastic correlation coefficient algorithm with a stochastic stepwise algorithm. We conduct extensive experimental comparison of our algorithm and other methods using two simulation studies and four real-life data sets. The results confirm that the proposed VSE leads to promising improvement on variable selection and regression accuracy.  相似文献   
3.
The authors consider dimensionality reduction methods used for prediction, such as reduced rank regression, principal component regression and partial least squares. They show how it is possible to obtain intermediate solutions by estimating simultaneously the latent variables for the predictors and for the responses. They obtain a continuum of solutions that goes from reduced rank regression to principal component regression via maximum likelihood and least squares estimation. Different solutions are compared using simulated and real data.  相似文献   
4.
高可用性系统的研究与实现   总被引:3,自引:0,他引:3  
研究了高可用系统的结构,介绍了一种高可用系统的实现。在分析系统失效因素和高可用系统结构的基础上,对主要的失效部分(软硬件)进行冗余以提高服务器、磁盘、网络可靠性,据此采用有效的失效探测与恢复机制,实现了一个能够保证整机容错,无单点失效的高可靠系统。  相似文献   
5.
考虑现实条件下交通网络的不确定性状态,提出了从确定型网络到不确定型网络状态下出行者路径选择行为的改变,及基于行程时间可靠性的路径选择模型。并将可靠行程时间的路径选择行为纳入到随机交通网络平衡分配模型中,证明了模型的等价性和唯一性。在一个小型测试网络上对模型分配结果进行了测试,测试结果与经验相吻合,表明模型具有较好的现实可行性。  相似文献   
6.
Some program managers share a common belief that adding a redundant component to a system reduces the probability of failure by half. This is true only if the failures of the redundant components are independent events, which is rarely the case. For example, the redundant components may be subjected to the same external loads. There is, however, in general a decrease in the failure probability of the system. Nonetheless, the redundant element comes at a cost, even if it is less than that of developing the first one when both are based on the same design. Identical parts save the most in terms of design costs, but are subjected to common failure modes from possible design errors that limit the effectiveness of the redundancy. In the development of critical systems, managers thus need to decide if the costs of a parallel system are justified by the increase in the system's reliability. NASA, for example, has used redundant spacecraft to increase the chances of mission success, which worked well in the cases of the Viking and Voyager missions. These two successes, however, do not guarantee future ones. We present here a risk analysis framework accounting for dependencies to support the decision to launch at the same time a twin mission of identical spacecraft, given incremental costs and risk-reduction benefits of the second one. We illustrate this analytical approach with the case of the Mars Exploration Rovers launched by NASA in 2003, for which we had performed this assessment in 2001.  相似文献   
7.
设计实现了一个基于串行口通信的双Web服务器的冗余系统,详细介绍了基于串行通信口的实现方法,并对冗余系统的原理和实现过程进行了分析。  相似文献   
8.
冗余是人类语言的固有特征。冗余现象的研究在语言学中占据重要地位,它对语言教学的影响也日益受到重视。本文利用语言测试手段,通过实验验证了冗余理论在英语教学中的积极作用  相似文献   
9.
汉字的“象”性构造和多样性外衍指向,使古代文论的表达具有简约和繁复两种风格。对于深刻的义理用以少总多或具象隐喻“一语而尽”;对于经验世界的多样性,则上下左右反复详言之,使“情貌无遗”。这两种风格,使文论述说表现出虚实相生、繁简结合的诗性之美。  相似文献   
10.
前修时贤说《蒙》卦初六爻之贞兆辞“以往吝”,歧义颇多。本文通过对《周易》古经含“往”字的句式的归纳分析,认为“以往吝”之“以”为衍文。  相似文献   
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