Department of Epidemiology, GROW - School for Oncology and Developmental Biology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands.
J Clin Epidemiol. 2021 Jun;134:113-124. doi: 10.1016/j.jclinepi.2021.01.022. Epub 2021 Feb 4.
Effect modification and interaction are important concepts for answering causal questions about interdependent effects of two (or more) exposures on some outcome of interest. Although conceptually alike and often mistakenly regarded as synonymous, effect modification and interaction actually refer to slightly different concepts when considered from a causal perspective. Their subtle yet relevant distinction lies in how the interplay between exposures is defined and the causal roles attributed to the exposures involved in the effect modification and interaction. To gain more insight into similarities and differences between the concepts of effect modification and interaction, the counterfactual theory of causation, albeit complicated, can be very helpful. Therefore, this article presents a nontechnical explanation of the counterfactual definition of effect modification and interaction. Essentially, effect modification and interaction are reflections of the reality and complexity of multicausality. The causal effect of an exposure of interest often depends on the levels of other exposures (effect modification) or causal effects of other exposures (interaction). Consequently, exposure effects should not be regarded in isolation but in combination. Understanding the underlying principles of effect modification and interaction on a conceptual level enables researchers to better anticipate, detect, and interpret these causal phenomena when setting up, analyzing, and reporting findings of (clinical) epidemiological studies. Effect modification and interaction are not biases to be avoided but properties of causal effects that ought to be unveiled. Hence, evidence for effect modification and interaction needs to be shown in order to delineate in whom and which instances causal effects occur.
当涉及因果关系时，效应修饰和交互作用是两个重要的概念，用于回答两个（或更多）暴露因素对感兴趣的结果的相互影响的因果问题。尽管从概念上讲它们相似，并且经常被误认为是同义词，但实际上，从因果角度考虑，它们指的是略有不同的概念。它们的细微但相关的区别在于如何定义暴露因素之间的相互作用以及归因于效应修饰和相互作用中涉及的暴露因素的因果作用。为了更深入地了解效应修饰和相互作用概念之间的相似之处和区别，尽管因果关系的反事实理论很复杂，但它可以非常有帮助。因此，本文对效应修饰和相互作用的反事实定义进行了非技术性的解释。本质上，效应修饰和相互作用反映了多因果关系的现实和复杂性。感兴趣的暴露因素的因果效应通常取决于其他暴露因素的水平（效应修饰）或其他暴露因素的因果效应（相互作用）。因此，暴露因素的效应不应孤立看待，而应综合考虑。在概念层面上理解效应修饰和相互作用的基本原理，使研究人员能够在设计、分析和报告（临床）流行病学研究的结果时更好地预测、检测和解释这些因果现象。效应修饰和相互作用不是要避免的偏差，而是应该揭示的因果效应的属性。因此，需要显示效应修饰和相互作用的证据，以便在谁和哪些情况下出现因果效应。
