共查询到20条相似文献,搜索用时 0 毫秒
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Inverse sampling is considered to be a more appropriate sampling scheme than the usual binomial sampling scheme when subjects arrive sequentially, when the underlying response of interest is acute, and when maximum likelihood estimators of some epidemiologic indices are undefined. In this article, we study various statistics for testing non-unity rate ratios in case-control studies under inverse sampling. These include the Wald, unconditional score, likelihood ratio and conditional score statistics. Three methods (the asymptotic, conditional exact, and Mid-P methods) are adopted for P-value calculation. We evaluate the performance of different combinations of test statistics and P-value calculation methods in terms of their empirical sizes and powers via Monte Carlo simulation. In general, asymptotic score and conditional score tests are preferable for their actual type I error rates are well controlled around the pre-chosen nominal level, and their powers are comparatively the largest. The exact version of Wald test is recommended if one wants to control the actual type I error rate at or below the pre-chosen nominal level. If larger power is expected and fluctuation of sizes around the pre-chosen nominal level are allowed, then the Mid-P version of Wald test is a desirable alternative. We illustrate the methodologies with a real example from a heart disease study. 相似文献
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Zhang Z 《Biometrical journal. Biometrische Zeitschrift》2006,48(6):948-965
There has been growing interest, when comparing an experimental treatment with an active control with respect to a binary outcome, in allowing the non-inferiority margin to depend on the unknown success rate in the control group. It does not seem universally recognized, however, that the statistical test should appropriately adjust for the uncertainty surrounding the non-inferiority margin. In this paper, we inspect a naive procedure that treats an \"observed margin\" as if it were fixed a priori, and explain why it might not be valid. We then derive a class of tests based on the delta method, including the Wald test and the score test, for a smooth margin. An alternative derivation is given for the asymptotic distribution of the likelihood ratio statistic, again for a smooth margin. We discuss the asymptotic behavior of these tests when applied to a piecewise smooth margin. A simple condition on the margin function is given which allows the likelihood ratio test to carry over to a piecewise smooth margin using the same critical value as for a smooth margin. Simulation experiments are conducted, under a smooth margin and a piecewise linear margin, to evaluate the finite-sample performance of the asymptotic tests studied. 相似文献
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Robust properties of likelihood ratio tests 总被引:2,自引:0,他引:2
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Yulan Li David Birkes David R. Thomas 《Biometrical journal. Biometrische Zeitschrift》1996,38(8):961-972
Residual maximum likelihood has proved to be a successful approach to the estimation of variance components. In this paper, its counterpart in testing, the residual likelihood ratio test, is applied to testing the ratio of two variance components. The test is compared with the Wald test and the locally most powerful invariant test. 相似文献
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Sequences for multiple protein-coding genes are now commonly available from several, often closely related species. These data sets offer intriguing opportunities to test hypotheses regarding whether different types of genes evolve under different selective pressures. Although maximum likelihood (ML) models of codon substitution that are suitable for such analyses have been developed, little is known about the statistical properties of these tests. We use a previously developed fixed-sites model and computer simulations to examine the accuracy and power of the likelihood ratio test (LRT) in comparing the nonsynonymous-to-synonymous substitution rate ratio (=dN/dS) between two genes. Our results show that the LRT applied to fixed-sites models may be inaccurate in some cases when setting significance thresholds using a 2 approximation. Instead, we use a parametric bootstrap to describe the distribution of the LRT statistic for fixed-sites models and examine the power of the test as a function of sampling variables and properties of the genes under study. We find that the power of the test is high (>80%) even when sampling few taxa (e.g., six species) if sequences are sufficiently diverged and the test is largely unaffected by the tree topology used to simulate data. Our simulations show fixed-sites models are suitable for comparing substitution parameters among genes evolving under even strong evolutionary constraint ( 0.05), although relative rate differences of 25% or less may be difficult to detect.Reviewing Editor: Dr. Rosmus Nielsen 相似文献
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Nonlinear component of variance models 总被引:1,自引:0,他引:1
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Testing in normal mixture models when the proportions are known 总被引:3,自引:0,他引:3
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The underlying structure of nonnested hypothesis tests 总被引:2,自引:0,他引:2
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Higher-order inference about a scalar parameter in the presenceof nuisance parameters can be achieved by bootstrapping, incircumstances where the parameter of interest is a componentof the canonical parameter in a full exponential family. Theoptimal test, which is approximated, is a conditional one basedon conditioning on the sufficient statistic for the nuisanceparameter. A bootstrap procedure that ignores the conditioningis shown to have desirable conditional properties in providingthird-order relative accuracy in approximation of p-values associatedwith the optimal test, in both continuous and discrete models.The bootstrap approach is equivalent to third-order analyticalapproaches, and is demonstrated in a number of examples to givevery accurate approximations even for very small sample sizes. 相似文献
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A note on 'Testing the number of components in a normal mixture' 总被引:1,自引:0,他引:1
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