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arXiv 1804.04557stat.ME
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基于t分布检验的非迭代样本量方法

A noniterative sample size procedure for tests based on t distributions

Yongqiang Tang

摘要:

本文对Guenther(1981)的单样本和双样本t检验方法进行了改进和扩展,提出了一种基于t分布的一般假设检验的非迭代样本量方法。在随机临床试验中,采用广义程序确定使用协方差分析(ANCOVA)和重复测量混合效应模型(MMRM)进行治疗比较的样本量。通过向正态近似的样本量添加几个简单的校正项来计算样本量,以解释t统计量和低阶方差项的非正态性,这些项是模型中协变量的函数。但它不需要指定协变量分布。非迭代程序适用于优效性检验、非劣效性检验和等效性或生物等效性检验的特殊情况,通常在四舍五入为整数后得到精确或接近精确的样本量估计值。将优效性试验中方差不等的两样本t检验的精确把握度的计算方法推广到等效性试验中。我们还推导了ANCOVA和MMRM的精确幂公式,并且ANCOVA的公式对于正态分布的协变量是精确的。数值算例表明,特别是在小样本所提出的方法的准确性。

英文摘要:

A noniterative sample size procedure is proposed for a general hypothesis test based on the t distribution by modifying and extending Guenther's (1981) approach for the one sample and two sample t tests. The generalized procedure is employed to determine the sample size for treatment comparisons using the analysis of covariance (ANCOVA) and the mixed effects model for repeated measures (MMRM) in randomized clinical trials. The sample size is calculated by adding a few simple correction terms to the sample size from the normal approximation to account for the nonnormality of the t statistic and lower order variance terms, which are functions of the covariates in the model. But it does not require specifying the covariate distribution. The noniterative procedure is suitable for superiority tests, noninferiority tests and a special case of the tests for equivalence or bioequivalence, and generally yields the exact or nearly exact sample size estimate after rounding to an integer. The method for calculating the exact power of the two sample t test with unequal variance in superiority trials is extended to equivalence trials. We also derive accurate power formulae for ANCOVA and MMRM, and the formula for ANCOVA is exact for normally distributed covariates. Numerical examples demonstrate the accuracy of the proposed methods particularly in small samples.

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