The overall effect of an exposure on an outcome, in the presence of a mediator with which the exposure may interact, can be decomposed into four components that correspond to the portion of the effect that is due: (i) to neither mediation nor interaction; (ii) to just interaction (but not mediation); (iii) to both mediation and interaction; and (iv) to just mediation (but not interaction). This four-way decomposition unifies methods to attribute effects to interactions and methods that assess mediation. We introduce the Stata command med4way to estimate the causal contrasts that arise in this decomposition. Med4way is implemented as a Stata stand-alone command requiring Stata version 10 or higher (StataCorp, College Station, TX, USA), and allows estimating the four-way decomposition using parametric regression models. Med4way can be used when the outcome is continuous, dichotomous, count or survival time, and the mediator is continuous or binary. The command accommodates cohort and case-control designs. We present two examples of application of the command to gain insight on important public health problems. In the first application, we employ med4way to investigate the role of birth outcomes in explaining the effect of maternal exposure to manganese on child neurodevelopment. In the second application, we investigate the role of stage at diagnosis in explaining income disparities in colorectal cancer survival. The command is freely available on GitHub [https://github.com/anddis/med4way] and has been published under General Public License (GPL) version 3.

中文翻译：

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Med4way：使用四向效应分解研究中介和交互机制的 Stata 命令


在存在可能与暴露相互作用的中介因素的情况下，暴露对结果的总体影响可以分解为四个部分，这些部分对应于归因于的影响部分：（i）既不是中介也不是相互作用； (ii) 公正互动（而非调解）； (iii) 调解和互动； (iv) 仅进行调解（而非互动）。这种四向分解统一了将效应归因于交互作用的方法和评估中介的方法。我们引入 Stata 命令med4way来估计此分解中出现的因果对比。 Med4way作为 Stata 独立命令实现，需要 Stata 版本 10 或更高版本（StataCorp，College Station，TX，USA），并允许使用参数回归模型估计四路分解。当结果是连续、二分、计数或生存时间，并且中介是连续或二元时，可以使用Med4way 。该命令适应队列和病例对照设计。我们提供了两个应用该命令来深入了解重要公共卫生问题的示例。在第一个应用中，我们采用med4way来研究出生结局在解释母亲接触锰对儿童神经发育的影响方面的作用。在第二个应用中，我们研究了诊断阶段在解释结直肠癌生存收入差异中的作用。该命令可在 GitHub [https://github.com/anddis/med4way] 上免费获取，并已根据通用公共许可证 (GPL) 版本 3 发布。