检索结果-南通市图书馆

Plausible combinations: An improved method to evaluate the covariate structure of Cormack-Jolly-Seber mark-recapture models

在线全文

学校读者我要写书评

暂无评论

Open Journal of Ecology 2013年第1期3卷 11-22页

作者： Jeffrey F. Bromaghin Trent L. McDonald Steven C. Amstrup Polar Bears International Bozeman USA US Geological Survey Alaska Science Center Anchorage USA Western Ecosystems Technology Inc. Cheyenne USA

Mark-recapture models are extensively used in quantitative population ecology, providing estimates of population vital rates, such as survival, that are difficult to obtain using other methods. Vital rates are commonly modeled as functions of explanatory covariates, adding considerable flexibility to mark-recapture models, but also increasing the subjectivity and complexity of the modeling process. Consequently, model selection and the evaluation of covariate structure remain critical aspects of mark-recapture modeling. The difficulties involved in model selection are compounded in Cormack-Jolly-Seber models because they are composed of separate sub-models for survival and recapture probabilities, which are conceptualized independently even though their parameters are not statistically independent. The construction of models as combinations of sub-models, together with multiple potential covariates, can lead to a large model set. Although desirable, estimation of the parameters of all models may not be feasible. Strategies to search a model space and base inference on a subset of all models exist and enjoy widespread use. However, even though the methods used to search a model space can be expected to influence parameter estimation, the assessment of covariate importance, and therefore the ecological interpretation of the modeling results, the performance of these strategies has received limited investigation. We present a new strategy for searching the space of a candidate set of Cormack-Jolly-Seber models and explore its performance relative to existing strategies using computer simulation. The new strategy provides an improved assessment of the importance of covariates and covariate combinations used to model survival and recapture probabilities, while requiring only a modest increase in the number of models on which inference is based in comparison to existing techniques.

关键词： Capture-Recapture Survival Model Building Model Selection Model Averaging Multi-Model Inference covariates covariate Weights CJS Akaike’s Information Criterion AIC AICC

An integrated method of selecting environmental covariates for predictive soil depth mapping

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Integrative Agriculture 2019年第2期18卷 301-315页

作者： LU Yuan-yuan LIU Feng ZHAO Yu-guo SONG Xiao-dong ZHANG Gan-lin State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil ScienceChinese Academy of SciencesNanjing 210008P.R.China University of Chinese Academy of Sciences Beijing 100049P.R.China

Environmental covariates are the basis of predictive soil *** selection determines the performance of soil mapping to a great extent,especially in cases where the number of soil samples is limited but soil spatial heterogeneity is *** this study,we proposed an integrated method to select environmental covariates for predictive soil depth ***,candidate variables that may influence the development of soil depth were selected based on pedogenetic ***,three conventional methods(Pearson correlation analysis(PsCA),generalized additive models(GAMs),and Random Forest(RF))were used to generate optimal combinations of environmental ***,three optimal combinations were integrated to produce a final combination based on the importance and occurrence frequency of each environmental *** tested this method for soil depth mapping in the upper reaches of the Heihe River Basin in Northwest China.A total of 129 soil sampling sites were collected using a representative sampling strategy,and RF and support vector machine(SVM)models were used to map soil *** results showed that compared to the set of environmental covariates selected by the three conventional selection methods,the set of environmental covariates selected by the proposed method achieved higher mapping *** combination from the proposed method obtained a root mean square error(RMSE)of 11.88 cm,which was 2.25–7.64 cm lower than the other methods,and an R^2 value of 0.76,which was 0.08–0.26 higher than the other *** results suggest that our method can be used as an alternative to the conventional methods for soil depth mapping and may also be effective for mapping other soil properties.

关键词： environmental covariate selection integrated method predictive soil mapping soil depth

Marginal Distribution Plots for Proportional Hazards Models with Time-Dependent covariates or Time-Varying Regression Coefficients

在线全文

学校读者我要写书评

暂无评论

Open Journal of Statistics 2017年第1期7卷 92-111页

作者： Qiqing Yu Junyi Dong George Wong Department of Mathematical Sciences SUNY Binghamton NY USA Department of Integrative Medicine Mount Sinai Beth Israel New York NY USA

Given a sample of regression data from (Y, Z), a new diagnostic plotting method is proposed for checking the hypothesis H0: the data are from a given Cox model with the time-dependent covariates Z. It compares two estimates of the marginal distribution FY of Y. One is an estimate of the modified expression of FY under H0, based on a consistent estimate of the parameter under H0, and based on the baseline distribution of the data. The other is the Kaplan-Meier-estimator of FY, together with its confidence band. The new plot, called the marginal distribution plot, can be viewed as a test for testing H0. The main advantage of the test over the existing residual tests is in the case that the data do not satisfy any Cox model or the Cox model is mis-specified. Then the new test is still valid, but not the residual tests and the residual tests often make type II error with a very large probability.

关键词： Cox’s Model Time-Dependent covariate Semi-Parametric Set-Up Diagnostic Plot

A Simulation Study on Comparing General Class of Semiparametric Transformation Models for Survival Outcome with Time-Varying Coefficients and covariates

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Open Journal of Statistics 2019年第2期9卷 169-180页

作者： Yemane Hailu Fissuh Tsegay Giday Woldu Idriss Abdelmajid Idriss Ahmed Abebe Zewdie Kebebe Department of Statistics College of Applied Sciences Beijing University of Technology Beijing China Department of Statistics College of Natural and Computational Sciences Aksum University Aksum Ethiopia Department of Mathematics College of Applied Sciences Beijing University of Technology Beijing China School of Software Engineering Faculty of Information Technology Beijing University of Technology Beijing China

The consideration of the time-varying covariate and time-varying coefficient effect in survival models are plausible and robust techniques. Such kind of analysis can be carried out with a general class of semiparametric transformation models. The aim of this article is to develop modified estimating equations under semiparametric transformation models of survival time with time-varying coefficient effect and time-varying continuous covariates. For this, it is important to organize the data in a counting process style and transform the time with standard transformation classes which shall be applied in this article. In the situation when the effect of coefficient and covariates change over time, the widely used maximum likelihood estimation method becomes more complex and burdensome in estimating consistent estimates. To overcome this problem, alternatively, the modified estimating equations were applied to estimate the unknown parameters and unspecified monotone transformation functions. The estimating equations were modified to incorporate the time-varying effect in both coefficient and covariates. The performance of the proposed methods is tested through a simulation study. To sum up the study, the effect of possibly time-varying covariates and time-varying coefficients was evaluated in some special cases of semiparametric transformation models. Finally, the results have shown that the role of the time-varying covariate in the semiparametric transformation models was plausible and credible.

关键词： Estimating Equation Semiparametric Transformation Models Time-to-Event Outcomes Time-Varying Coefficients Time-Varying covariate

Imputed Empirical Likelihood for Varying Coefficient Models with Missing covariates

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Open Journal of Applied Sciences 2013年第1期3卷 44-48页

作者： Peixin Zhao Department of Mathematics Hechi University Guangxi Yizhou China

The empirical likelihood-based inference for varying coefficient models with missing covariates is investigated. An imputed empirical likelihood ratio function for the coefficient functions is proposed, and it is shown that iis limiting distribution is standard chi-squared. Then the corresponding confidence intervals for the regression coefficients are constructed. Some simulations show that the proposed procedure can attenuate the effect of the missing data, and performs well for the finite sample.

关键词： Empirical Likelihood Varying Coefficient Model Missing covariate

ESTIMATION OF WATER TABLE ELEVATION BY UNIVERSAL COKRIGING

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2005年第2期17卷 154-163页

作者： CHENJia-jun TIANKai-ming GUOQiao-yu StateKeyJointLaboratoryofEnvironmentalSimulationandPollutionControl InstituteofEnvironmentalSciencesBeijingNormalUniversityBeijing100875China ChinaUniversityofGeosciences Beijing100083China StateKeyJointLaboratoryofEnvironmentalSimulationandPollutionControl.InstituteofEnvironmentalSciences BeijingNormalUniversityBeijing100875China

When water resource or quality problems associated with phreatic water in geological settings are studied, information about water table elevations is often crucial. In those cases where the water table is a subdued replica of the ground surface, universal cokriging can be used to estimate water table elevations at un-sampled locations on the basis of water table and ground surface elevation measurements obtained at well locations. In this paper, universal cokriging, with ground surface elevation considered as a co-variate, was used to estimate water table elevations. Universal cokriging equations were derived, an iterative method for obtaining experimental variograms was established, and a case study of an initial groundwater flow simulation in the Xiuwu County, Henan Province, China, was presented. In the case study, the initial groundwater flow regime was represented both by universal cokriging with the ground surface elevation serving as a covariate and by universal kriging without the inclusion of ground surface elevation as a covariate. A comparison of the results from these two approaches shows that groundwater levels of phreatic water at locations without measurements in regions with unconsolidated porous media can be estimated more accurately by universal cokriging.

关键词： water table estimation universal cokriging covariate ground surface elevation variogram

Approach to the Relation of Mutual-Feed Joint-Variation in Groundwater Management Model

在线全文

学校读者我要写书评

暂无评论

Journal of Earth Science 2012年第3期23卷 349-358页

作者：李平卢文喜靳孟贵杨青春 College of Chemistry and Materials South-Central University for Nationalities School of Environmental Studies China University of Geosciences College of Environment and Resources Jilin University

In groundwater management,the exchanges between groundwater and other water such as surface water and spring water need to be *** exchange is dependent on the ground-water level,which is called *** pumping rate,groundwater level,and covariate interact and the relation of mutual-feed joint-variation is used to describe their *** article presents a new approach of dealing with the relation in groundwater management *** mathematical for-mulation of the relation,as an additional equality constraint in the optimization model,is developed using response matrix *** the groundwater management model with covariate is set *** code for the simulation and management of groundwater system with covariate is programmed with Fortran 90,and the optimal pumping rate,groundwater level,and covariate are *** approach is verified with a hypothetical ***,the approach is applied to the groundwater management of Qianguo（前郭） area in western Jilin（吉林） *** results indicate that the ap-proach is *** provides a universal solution for various covariates and reduces the computational complexity compared to iteration *** approach is proven to be very efficient to solve ground-water management problem with covariate.

关键词： covariate relation of mutual-feed joint-variation groundwater management response matrix

Deterministic wave prediction model for irregular long-crested waves with Recurrent Neural Network

在线全文

学校读者我要写书评

暂无评论

Journal of Ocean Engineering and Science 2024年第3期9卷 251-263页

作者： Yue Liu Xiantao Zhang Gang Chen Qing Dong Xiaoxian Guo Xinliang Tian Wenyue Lu Tao Peng State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University(SJTU)Shanghai 200240China SJTU Yazhou Bay Institute of Deepsea Technology SanyaHainan572000China

Real-time predicting of stochastic waves is crucial in marine *** this paper,a deep learning wave prediction(Deep-WP)model based on the‘probabilistic’strategy is designed for the short-term prediction of stochastic *** Deep-WP model employs the long short-term memory(LSTM)unit to collect pertinent information from the wave elevation time *** irregular long-crested waves generated in the deepwater offshore basin at Shanghai Jiao Tong University are used to validate and optimize the Deep-WP *** the prediction duration is 1.92s,2.56s,and,3.84s,respectively,the predicted results are almost identical with the ground *** the prediction duration is increased to 7.68s or 15.36s,the Deep-WP model’s error increases,but it still maintains a high level of accuracy during the first few *** introduction of covariates will improve the Deep-WP model’s performance,with the absolute position and timestamp being particularly advantageous for wave ***,the Deep-WP model is applicable to predict waves with different energy *** proposed Deep-WP model shows a feasible ability to predict nonlinear stochastic waves in real-time.

关键词： Real-time wave prediction Probability LSTM covariate

Statistical issues in randomised controlled trials: a narrative synthesis

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Asian Pacific Journal of Tropical Biomedicine 2015年第5期5卷 354-359页

作者： Bolaji Emmanuel Egbewale Department of Community Medicine Ladoke Akintola University of Technology

Randomised controlled trials(RCTs) are gold standard in the evaluation of treatment efficacy in medical investigations, only if well designed and implemented. Till date, distorted views and misapplications of statistical procedures involved in RCTs are still in practice. Hence, clarification of concepts and acceptable practices related to certain statistical issues involved in the design, conduct and reporting of randomised controlled trials is needed. This narrative synthesis aimed at providing succinct but clear information on the concepts and practices of selected statistical issues in RCTs to inform correct applications. The use of tests of significance is no longer acceptable as means to compare baseline similarity between treatment groups and in determining which covariate(s) should be included in the model for adjustment. Distribution of baseline attributes simply presented in tabular form is however, rather preferred. Regarding covariate selection, such approach that makes use of information on the degree of correlation between the covariate(s) and the outcome variable is more in tandem with statistical principle(s) than that based on tests of significance. Stratification and minimisation are not alternatives to covariate adjusted analysis; in fact they establish the need for one. Intention-totreat is the preferred approach for the evaluation of primary outcome measures and researchers have responsibility to report whether or not the procedure was followed. A major use of results from subgroup analysis is to generate hypothesis for future clinical trials. Since RCTs are gold standard in the comparison of medical interventions, researchers cannot afford the practices of distorted allocation or statistical procedures in this all important experimental design method.

关键词： Baseline comparability covariate selection for adjustment covariate adjustment Intention-to-treat analysis Subgroup analysis