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首页> 外文期刊>Statistics in medicine >Operating characteristics of sample size re-estimation with futility stopping based on conditional power.
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Operating characteristics of sample size re-estimation with futility stopping based on conditional power.

机译:样本大小的重新估计的操作特性,并根据条件功率停止了徒劳的工作。

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摘要

Various methods have been described for re-estimating the final sample size in a clinical trial based on an interim assessment of the treatment effect. Many re-weight the observations after re-sizing so as to control the pursuant inflation in the type I error probability alpha. Lan and Trost (Estimation of parameters and sample size re-estimation. Proceedings of the American Statistical Association Biopharmaceutical Section 1997; 48-51) proposed a simple procedure based on conditional power calculated under the current trend in the data (CPT). The study is terminated for futility if CPT < or = CL, continued unchanged if CPT > or = CU, or re-sized by a factor m to yield CPT = CU if CL < CPT < CU, where CL and CU are pre-specified probability levels. The overall level alpha can be preserved since the reduction due to stopping for futility can balance the inflation due to sample size re-estimation, thus permitting any form of final analysis with no re-weighting. Herein the statistical properties of this approach are described including an evaluation of the probabilities of stopping for futility or re-sizing, the distribution of the re-sizing factor m, and the unconditional type I and II error probabilities alpha and beta. Since futility stopping does not allow a type I error but commits a type II error, then as the probability of stopping for futility increases, alpha decreases and beta increases. An iterative procedure is described for choice of the critical test value and the futility stopping boundary so as to ensure that specified alpha and beta are obtained. However, inflation in beta is controlled by reducing the probability of futility stopping, that in turn dramatically increases the possible re-sizing factor m. The procedure is also generalized to limit the maximum sample size inflation factor, such as at m max = 4. However, doing so then allows for a non-trivial fraction of studies to be re-sized at this level that still have low conditional power. These properties also apply to other methods for sample size re-estimation with a provision for stopping for futility. Sample size re-estimation procedures should be used with caution and the impact on the overall type II error probability should be assessed.
机译:已经描述了用于基于治疗效果的中期评估来重新估计临床试验中的最终样本量的各种方法。许多人在调整大小后重新加权了观测值,以将相应的通货膨胀控制在I型错误概率alpha中。 Lan和Trost(估计参数和重新估计样本大小。美国统计协会生物制药分会的会议记录,1997; 48-51)提出了一种简单的程序,该程序基于在数据的当前趋势下计算出的条件功率(CPT)。如果CPT <或= CL,则研究无济于事;如果CPT>或= CU,则研究继续不变;如果CL

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