A popular way to reduce confounding in observational studies is to use each study participant as his or her own control. This is possible when both the exposure and the outcome are time varying and have been measured at several time points for each individual. The case-time-control method is a special case, which, under certain assumptions, allows the analyst to control for confounding by time-varying covariates, while controlling for all time-stationary characteristics of the study participants. There are two formulations of the case-time-control method. One formulation requires that the exposure be binary, and the other requires that there be no more than two time points per individual. In this article the author proposes a generalization of the case-time-control method for nonbinary exposures and an arbitrary number of time points. The author derives the asymptotic properties of the resulting estimator and assesses its finite sample properties in a simulation study.

中文翻译：

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非二元曝光的案例时间控制方法

在观察性研究中减少混淆的一种流行方法是使用每个研究参与者作为他或她自己的对照。当暴露和结果都随时间变化并且已在每个人的多个时间点测量时，这是可能的。案例时间控制方法是一种特殊情况，在某些假设下，它允许分析师控制时变协变量的混杂，同时控制研究参与者的所有时间平稳特征。病例-时间-控制方法有两种形式。一种公式要求暴露是二元的，另一种公式要求每个人不超过两个时间点。在本文中，作者提出了对非二元暴露和任意数量时间点的病例-时间-控制方法的概括。