In a clinical study comparing the failure probabilities of two condom types, the sample of all reported acts of intercourse in which a study condom was used by a randomized participant is typically defined to be the primary analysis sample. However, it may also be desirable to make comparisons among only those acts in which the participants correctly followed all condom use instructions before, during, and after the act of intercourse (i.e., the "correct-use" subset). The timing associated with the definition of correct use creates a dilemma in that an act cannot be classified as a "correct-use act" until after the completion of both intercourse and withdrawal; if a condom fails (e.g., breaks or slips completely off of the penis) during intercourse then the couple has no chance at correct use during withdrawal. As a result of the implicitly conditional nature of this problem, it is not a simple matter to specify a correct-use subset of the primary analysis sample. With this in mind, we develop estimators for the correct-use failure probabilities, the corresponding standard errors, and test statistics for comparing the correct-use failure probabilities between condom groups. We demonstrate the utility of the proposed methods by applying them to data from a clinical study of condom contraceptive effectiveness, and we use simulated data to investigate the finite sample properties of the proposed methods. The simulation results indicate that one of our proposed estimators is at least approximately unbiased, even in small samples. Furthermore, one-sided noninferiority tests performed using this estimator tend to have sizes that are only marginally larger than the nominal test size in moderate to large samples.

译文

在一项比较两种避孕套失败概率的临床研究中,随机参与者使用研究避孕套的所有报告的性交行为的样本通常被定义为主要分析样本。然而,也可能希望仅在参与者在性交行为之前、期间和之后正确遵循所有避孕套使用说明的那些行为 (即,“正确使用” 子集) 之间进行比较。与正确使用的定义相关的时机造成了一个两难境地,即在性交和戒断完成之前,一项行为不能被归类为 “正确使用行为”; 如果避孕套失效 (例如,在性交过程中,这对夫妇在退出过程中没有机会正确使用阴茎。由于此问题的隐含条件性质,指定主要分析样本的正确使用子集并不是一件简单的事情。考虑到这一点,我们开发了正确使用的故障概率,相应的标准误差的估计器,以及用于比较安全套组之间正确使用的故障概率的测试统计数据。我们通过将所提出的方法应用于避孕套避孕有效性的临床研究数据来证明它们的实用性,并且我们使用模拟数据来研究所提出方法的有限样本属性。仿真结果表明,即使在小样本中,我们提出的估计量之一也至少近似无偏。此外,使用该估计器进行的单侧非劣效性检验的大小往往仅略大于中等至较大样本中的标称检验大小。

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