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1.
A bootstrap method suggested by COLLINGS and HAMILTON (1988) to estimate the power of the two-sample Wilcoxon test is adapted to use for estimating the power of the Gehan test. A Monte Carlo simulation study is done to determine how well the method works in this case.  相似文献   

2.
When analyzing biological data sets, a frequent problem is to estimate the pth quantile of a distribution, when that quantile is assumed to depend on a covariate; in the present paper the dependence of the quantile on the covariate is assumed to be monotonic. Some properties of an isotonic pth quantile regression, considered as an estimator of an increasing pth quantile function, are presented.  相似文献   

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Doguwa (1990) proposed kernel based pair-correlation function estimators for Point processes. These estimators transport a part of the probability mass into the negative or left, to a hard-core distance. The reflection technique is used to provide an alternative estimator of the pair-correlation function, which drastically reduces the bias inherent in these estimators for the case of random and clustered point patterns. However, the drastic reduction in bias, is at the cost of a much larger variance.  相似文献   

5.
There are a number of nonparametric procedures known for testing goodness-of-fit in the univariate case. Similar procedures can be derived for testing goodness-of-fit in the multivariate case through an application of the theory of statistically equivalent blocks (SEB). The SEB transforms the data into coverages which are distributed as spacings from a uniform distribution on [0,1], under the null hypothesis. In this paper, we present a multivariate nonparametric test of goodness-of-fit based on the SEB when the multivariate distributions under the null hypothesis and the alternative hypothesis are “weakly” ordered. Empirical results are given on the performance of the proposed test in an application to the problem of assessing the reliability of a p-component system.  相似文献   

6.
Kernel estimators are used to obtain new estimators for the tumour onset distribution and its density. Asymptotical properties of the estimators are studied and confidence tests are constructed.  相似文献   

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F. Perron  K. Mengersen 《Biometrics》2001,57(2):518-528
Nonparametric modeling is an indispensable tool in many applications and its formulation in an hierarchical Bayesian context, using the entire posterior distribution rather than particular expectations, increases its flexibility. In this article, the focus is on nonparametric estimation through a mixture of triangular distributions. The optimality of this methodology is addressed and bounds on the accuracy of this approximation are derived. Although our approach is more widely applicable, we focus for simplicity on estimation of a monotone nondecreasing regression on [0, 1] with additive error, effectively approximating the function of interest by a function having a piecewise linear derivative. Computationally accessible methods of estimation are described through an amalgamation of existing Markov chain Monte Carlo algorithms. Simulations and examples illustrate the approach.  相似文献   

9.
AZZALINI  A. 《Biometrika》1981,68(1):326-328
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Estimation of additive regression models with known links   总被引:4,自引:0,他引:4  
LINTON  O. B.; HARDLE  W. 《Biometrika》1996,83(3):529-540
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A new statistic Δ to test the hypothesis of a difference in the dispersion of two dependent samples of ordinal data quality is proposed. It draws on the idea of rank assignment originally forwarded by Siegel and Tukey (1960). No exact probability levels can be given for this statistic for the time being, but it is shown that the statistic is linearly related to the so-called Hotelling-Pabst statistic D, and that one can use exact tables of the latter as a substitute in the statistical decision process with small samples. For larger samples, an approximation of Δ to the standard normal distribution is given. The problem of tied observations is not sufficiently solved yet. A conservative procedure of rank assignment is proposed as long as the exact distribution of Δ in the presence of ties is unknown.  相似文献   

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Estimation from quasi life tables   总被引:2,自引:0,他引:2  
BAXTER  LAURENCE A. 《Biometrika》1994,81(3):567-577
A large number of identical components are simultaneously setinto operation at each of a regular sequence of times and, onfailure, a component is instantaneously replaced. The functionalform of the distribution of the component lifelength is assumedto be known and it is desired to estimate the parameters ofthis distribution. However, no observations of the lifelengthsof individual components have been recorded: the only informationavailable is the numbers of components which fail between successivetime points. It is shown how this information, in conjunctionwith the theory of recurrent events, may be used to constructa nonparametric estimator of the discretised lifelength distribution.The latter is then used to estimate the unknown parameters.  相似文献   

16.
It is shown that the KRUSKAL -WALLIS statistic may be decomposed into components designed to detect trends in the underlying distributions. Extensions to other K sample linear rank statistics and to nonparametric regression statistics are noted.  相似文献   

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A new design for estimating the distribution of time to pregnancy is proposed and investigated. The design is based on recording current durations in a cross-sectional sample of women, leading to statistical problems similar to estimating renewal time distributions from backward recurrence times. Non-parametric estimation is studied in some detail and a parametric approach is indicated. The results are illustrated on Monte Carlo simulations and on data from a recent European collaborative study. The role and applicability of this approach is discussed.  相似文献   

19.
The performance of diagnostic tests is often evaluated by estimating their sensitivity and specificity with respect to a traditionally accepted standard test regarded as a “gold standard” in making the diagnosis. Correlated samples of binary data arise in many fields of application. The fundamental unit for analysis is occasionally the site rather than the subject in site-specific studies. Statistical methods that take into account the within-subject corelation should be employed to estimate the sensitivity and the specificity of diagnostic tests since site-specific results within a subject can be highly correlated. I introduce several statistical methods for the estimation of the sensitivity and the specificity of sitespecific diagnostic tests. I apply these techniques to the data from a study involving an enzymatic diagnostic test to motivate and illustrate the estimation of the sensitivity and the specificity of periodontal diagnostic tests. I present results from a simulation study for the estimation of diagnostic sensitivity when the data are correlated within subjects. Through a simulation study, I compare the performance of the binomial estimator pCBE, the ratio estimator pCBE, the weighted estimator pCWE, the intracluster correlation estimator pCIC, and the generalized estimating equation (GEE) estimator PCGEE in terms of biases, observed variances, mean squared errors (MSE), relative efficiencies of their variances and 95 per cent coverage proportions. I recommend using PCBE when σ == 0. I recommend use of the weighted estimator PCWE when σ = 0.6. When σ == 0.2 or σ == 0.4, and the number of subjects is at least 30, PCGEE performs well.  相似文献   

20.
目的评价动物个体近交程度所需的遗传标记数量。方法通过计算机模拟动物近交系的建立过程,比较不同数量遗传标记估计的个体纯合度与相应世代近交系数的差异。结果 1000次模拟中各世代10个个体不同数量的标记组合计算的纯合度平均值与该世代个体的近交系数都存在差异,使用75个标记所获得的个体纯合度与相应近交系数差异最小的有8个世代,其他组合差异最小的世代为0~3个。随着标记数量的增加,单次模拟所获得标记基因纯合度的最大值和最小值逐渐向真实近交系数接近。结论使用少量的标记评价个体近交程度将存在较大的偏差,标记数量越少,偏差越大,当选用多态性丰富标记数接近75万个时,这种偏差会降到最低,标记数量进一步增大并不能提高评价的准确性。  相似文献   

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