排序方式: 共有8条查询结果,搜索用时 15 毫秒
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Hideyuki Douke 《统计学通讯:理论与方法》2013,42(12):3015-3029
In this study we discuss the group sequential procedures for comparing two treatments based on multivariate observations in clinical trials. Also we suppose that a response vector on each of two treatments has a multivariate normal distribution with unknown covariance matrix. Then we propose a group sequential x2 statistic in order to carry out repeated significance test for hypothesis of no difference between two population mean vectors. In order to realize the group sequential test where average sample number is reduced, we propose another modified group sequential x2 statistic by extension of Jennison and Turnbull ( 1991 ). After construction of repeated confidence boundaries for making the repeated significance test, we compare two group sequential procedures based on two statistics regarding the average sample number and the power of the test in the simulations. 相似文献
2.
Bivariate count data arise in several different disciplines (epidemiology, marketing, sports statistics just to name a few)
and the bivariate Poisson distribution being a generalization of the Poisson distribution plays an important role in modelling
such data. In the present paper we present a Bayesian estimation approach for the parameters of the bivariate Poisson model
and provide the posterior distributions in closed forms. It is shown that the joint posterior distributions are finite mixtures
of conditionally independent gamma distributions for which their full form can be easily deduced by a recursively updating
scheme. Thus, the need of applying computationally demanding MCMC schemes for Bayesian inference in such models will be removed,
since direct sampling from the posterior will become available, even in cases where the posterior distribution of functions
of the parameters is not available in closed form. In addition, we define a class of prior distributions that possess an interesting
conjugacy property which extends the typical notion of conjugacy, in the sense that both prior and posteriors belong to the
same family of finite mixture models but with different number of components. Extension to certain other models including
multivariate models or models with other marginal distributions are discussed. 相似文献
3.
“Step down” or “sequentially rejective” procedures for comparisons with a control are considered for both one sided and two sided comparisons. Confidence bounds (in terms of the control) are derived for those (location) parameters not in a selected set. Special results are derived for the normal distribution with unknown variance where the sample numbers are (possibly) unequal. 相似文献
4.
For fixed size sampling designs with high entropy, it is well known that the variance of the Horvitz–Thompson estimator can be approximated by the Hájek formula. The interest of this asymptotic variance approximation is that it only involves the first order inclusion probabilities of the statistical units. We extend this variance formula when the variable under study is functional, and we prove, under general conditions on the regularity of the individual trajectories and the sampling design, that we can get a uniformly convergent estimator of the variance function of the Horvitz–Thompson estimator of the mean function. Rates of convergence to the true variance function are given for the rejective sampling. We deduce, under conditions on the entropy of the sampling design, that it is possible to build confidence bands whose coverage is asymptotically the desired one via simulation of Gaussian processes with variance function given by the Hájek formula. Finally, the accuracy of the proposed variance estimator is evaluated on samples of electricity consumption data measured every half an hour over a period of 1 week. 相似文献
5.
Treatment regimes are algorithms for assigning treatments to patients with complex diseases, where treatment consists of more than one episode of therapy, potentially with different dosages of the same agent or different agents. Sequentially randomized clinical trials are usually designed to evaluate and compare the effect of different treatment regimes. In such designs, eligible patients are first randomly assigned to receive one of the initial treatments. Patients meeting some criteria (e.g. no progressive disease) are then randomized to receive one of the maintenance treatments. Usually, the procedure continues until all treatment options are exhausted. Such multistage treatment assignment results in treatment regimes consisting of initial treatments, intermediate responses and second-stage treatments. However, methods for efficient analysis of sequentially randomized trials have only been developed very recently. As a result, earlier clinical trials reported results based only on the comparison of stage-specific treatments. In this article, we propose a model that applies to comparisons of any combination of any number of treatment regimes regardless of the number of stages of treatment adjusted for auxiliary variables. Contrasts of treatment regimes are tested using the Wald chi-square method. Both the model and Wald chi-square tests of contrasts are illustrated through a simulation study and an application to a high-risk neuroblastoma study to complement the earlier results reported on this study. 相似文献
6.
Patrice Bertail Emilie Chautru Stephan Clémençon 《Scandinavian Journal of Statistics》2017,44(1):97-111
It is the main purpose of this paper to study the asymptotics of certain variants of the empirical process in the context of survey data. Precisely, Functional Central Limit Theorems are established under usual conditions when the sample is drawn from a Poisson or a rejective sampling design. The framework we develop encompasses sampling designs with non‐uniform first order inclusion probabilities, which can be chosen so as to optimize estimation accuracy. Applications to Hadamard differentiable functionals are considered. 相似文献
7.
Nairanjana Dasgupta John D. Spurrier Edward Martinez Barry C. Moore 《统计学通讯:模拟与计算》2013,42(4):1039-1057
We are interested in comparing logistic regressions for several test treatments or populations with a logistic regression for a standard treatment or population. The research was motivated by some real life problems, which are discussed as data examples. We propose a step-down likelihood ratio method for declaring differences between the test treatments or populations and the standard treatment or population. Competitors based on the sequentially rejective Bonferroni Wald statistic, sequentially rejective exact Wald statistic and Reiers?l's statistic are also discussed. It is shown that the proposed method asymptotically controls the probability of type I error. A Monte Carlo simulation shows that the proposed method performs well for relatively small sample sizes, outperforming its competitors. 相似文献
8.
The paper deals with uniform and D-optimality of designs in the two-way elimination of heterogeneities. It is shown that designs which are optimum for the hypothesis that all treatment effects are equal are optimum for some other hypotheses, too. The Proof is based on a new matrix- and determinantal inequality. 相似文献
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