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1.
Combining dependent tests with incomplete repeated measurements   总被引:9,自引:0,他引:9  
WEI  L. J.; JOHNSON  WAYNE E. 《Biometrika》1985,72(2):359-364
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In many clinical trials, it is desirable to establish a sequential monitoring plan, whereby the test statistic is computed at an interim point or points in the trial and a decision is made whether to stop early due to evidence of treatment efficacy. In this article, we will set up a sequential monitoring plan for randomization-based inference under the permuted block design, stratified block design, and stratified urn design. We will also propose a definition of information fraction in these settings and discuss its calculation under these different designs.  相似文献   

3.
Reiczigel J 《Biometrics》1999,55(4):1059-1063
Summary. Experimental data often consist of serial measurements on subjects after a treatment. Typical questions concerning such data are: (A) Do subjects really react to treatment or are the fluctuations just random? (B) What are the numerical characteristics of the response? (C) Is the response identical in all groups? Differences between the individuals in the dynamics of the reaction make it difficult to apply standard statistical procedures. This paper proposes to answer questions (A) and (B) at the individual level, then to give an answer to (C) on the basis of this information. This kind of analysis may be useful since it can separate subjects giving response from those that do not and can identify individual response patterns and compare treatments with respect to each numerical characteristic separately. To answer question (A), a permutation test is proposed and its power is evaluated by simulation.  相似文献   

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The behaviour of some significance tests under experimental randomization   总被引:1,自引:0,他引:1  
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9.
Two response indices characterizing the stimulus effect on spontaneously active neurons are developed. They are based on a non-parametric comparison of interspike interval distributions under the spontaneous and the stimulus condition. The response indices obtained with repeated stimuli can be combined into a single multiple-trial index. The method is tested both with different types of simulated spike activity and with actual single unit activity recorded from an auditory centre of a songbird.Supported by Deutsche Forschungsgemeinschaft within Sonderforschungsbereich 114 (Bionach)  相似文献   

10.
Randomization tests allow the formulation and statistical testing of null hypotheses about the quality of entire data sets or the quality of fit between the data and particular phylogenetic hypotheses. Randomization tests of phylogenetic hypotheses based on the concepts of split support and split conflict are described here, as are tests where splits, rather than the data, are randomly permuted. These tree-independent randomization tests are explored through their application to phylogenetic data for caecilian amphibians. Of these tests, split support randomization tests appear to be the most promising tools for phylogeneticists. These tests seem quite conservative, are applicable to nonpolar data and unordered multistate characters, and do not have the problems of nonindependence that affect split conflict and hierarchy tests. Unlike split conflict tests, their power does not appear to be correlated with split size. However, all tests are sensitive to taxonomic scope. Split support tests may help discern data that are likely to be affected by the problems of long-branches effects. Comparison of test results for mutually incompatible splits may help identify the presence of strong misleading signals in phylogenetic data. Significant split support could be a prerequisite for considering phylogenetic hypotheses to be well supported by the data, and split support randomization tests might be usefully applied prior to or as part of tree construction.  相似文献   

11.
A general class of nonparametric tests for survival analysis   总被引:1,自引:0,他引:1  
M P Jones  J Crowley 《Biometrics》1989,45(1):157-170
Tarone and Ware (1977, Biometrika 64, 156-160) developed a general class of s-sample test statistics for right-censored survival data that includes the log-rank and modified Wilcoxon procedures. Subsequently, many authors have considered two- and s-sample classes in detail. In this paper a family of nonparametric statistics is shown to unify existing and generate new test statistics for the s (greater than or equal to 2)-sample, s-sample trend, and single continuous covariate problems.  相似文献   

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E Brunner 《Biometrics》1991,47(3):1149-1153
In a nonparametric two-sample model for independent observations with repeated measurements, a new point estimator and a new distribution-free confidence interval for the difference in means are introduced. The method is based on some ideas in Hodges and Lehmann (1963, Annals of Mathematical Statistics 34, 598-611). The asymptotic theory in Brunner and Neumann (1983, Biometrical Journal 24, 373-389; 1986; Biometrical Journal 28, 394-402) and the results for small sample sizes in Brunner and Compagnone (1988, Statistical Software Newsletter 14, 36-42) are used. The new estimators are applied to a problem in morphometry.  相似文献   

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When the mode of inheritance of a disease is unknown, the LOD-score method of linkage analysis must take into account uncertainties in model parameters. We have previously proposed a parametric linkage test called "MFLOD," which does not require specification of disease model parameters. In the present study, we introduce two new model-free parametric linkage tests, known as "MLOD" and "MALOD." These tests are defined, respectively, as the LOD score and the admixture LOD score, maximized (subject to the same constraints as MFLOD) over disease-model parameters. We compared the power of these three parametric linkage tests and that of two nonparametric linkage tests, NPLall and NPLpairs, which are implemented in GENEHUNTER. With the use of small pedigrees and a fully informative marker, we found the powers of MLOD, NPLall, and NPLpairs to be almost equivalent to each other and not far below that of a LOD-score analysis performed under the assumption the correct genetic parameters. Thus, linkage analysis is not much hindered by uncertain mode of inheritance. The results also suggest that both parametric and nonparametric methods are suitable for linkage analysis of complex disorders in small pedigrees. However, whether these results apply to large pedigrees remains to be answered.  相似文献   

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Data from an ACTH challenge experiment with veal calves, two short time series of cortisol measurements per animal at 6 and 27 weeks of age, are analysed. Interest is focussed on variation in cortisol profiles both within and between animals. Potential effects of an animals diet and housing system on the profiles are addressed as well. Fully parametric and semi‐parametric models, combining individual random effects with effects of diet and housing, were fitted using (approximate) restricted maximum likelihood (employing Laplacian integration). Eigenfunctions were utilized to describe the variation between profiles and the connection between profiles of the same individual. All calculations were performed with standard software. Results of the analysis provides empirical support for the existence of stable individual characteristics mediating reactivity of the adrenal cortex.  相似文献   

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A null model for randomization tests of nestedness in species assemblages   总被引:7,自引:0,他引:7  
Analysis of the degree of order in species assemblages in terms of nested subsets has received increased interest during the last decade. However, recently a series of papers have questioned the validity of methods employed for testing whether observed patterns deviate from random expectations. The current view seems to be that the randomization procedure should control for both number of species per site and species frequencies. The randomization procedures used also choose to keep the total number of observations constant in each resample. In this paper I question some of these assumptions when analyzing species-by-site matrices for detecting whether the biota is significantly nested or not. My basic assumption is that the observed species frequency is only an estimate of the probability of occurrence for the particular species. For a test of degree of nestedness all sites should be regarded as being equal. To what extent size, isolation or habitat quality may influence species distribution is a secondary question if nestedness can be statistically proven. This implies that generation of random matrices should only consider the frequency of the species (as an estimate of their probability of occurring in any patch). Such matrices are computationally simple and besides providing a test of nestedness also open the possibility of testing whether the range in species richness is smaller or larger than expected under random expectations. The choice of null model for the test should always be viewed in relation to the question asked. If nestedness is concerned the methods proposed here should be used. However, if other questions are at hand the restrictions of previous approaches may be valid. This is for instance the case if pairwise species co-occurrences are analyzed. In this case, the richness of each site should obviously be incorporated in the randomization to control for the higher probability of co-occurrence at species-rich sites.  相似文献   

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Behavioural studies are commonly plagued with data that violate the assumptions of parametric statistics. Consequently, classic nonparametric methods (e.g. rank tests) and novel distribution-free methods (e.g. randomization tests) have been used to a great extent by behaviourists. However, the robustness of such methods in terms of statistical power and type I error have seldom been evaluated. This probably reflects the fact that empirical methods, such as Monte Carlo approaches, are required to assess these concerns. In this study we show that analytical methods cannot always be used to evaluate the robustness of statistical tests, but rather Monte Carlo approaches must be employed. We detail empirical protocols for estimating power and type I error rates for parametric, nonparametric and randomization methods, and demonstrate their application for an analysis of variance and a regression/correlation analysis design. Together, this study provides a framework from which behaviourists can compare the reliability of different methods for data analysis, serving as a basis for selecting the most appropriate statistical test given the characteristics of data at hand. Copyright 2001 The Association for the Study of Animal Behaviour.  相似文献   

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