, Atlanta, GA, 30322, USA.
Eur J Epidemiol. 2015 Oct;30(10):1089-99. doi: 10.1007/s10654-014-9915-2. Epub 2014 Jun 4.
Definitions and conceptualizations of confounding and selection bias have evolved over the past several decades. An important advance occurred with development of the concept of exchangeability. For example, if exchangeability holds, risks of disease in an unexposed group can be compared with risks in an exposed group to estimate causal effects. Another advance occurred with the use of causal graphs to summarize causal relationships and facilitate identification of causal patterns that likely indicate bias, including confounding and selection bias. While closely related, exchangeability is defined in the counterfactual-model framework and confounding paths in the causal-graph framework. Moreover, the precise relationships between these concepts have not been fully described. Here, we summarize definitions and current views of these concepts. We show how bias, exchangeability and biasing paths interrelate and provide justification for key results. For example, we show that absence of a biasing path implies exchangeability but that the reverse implication need not hold without an additional assumption, such as faithfulness. The close links shown are expected. However confounding, selection bias and exchangeability are basic concepts, so comprehensive summarization and definitive demonstration of links between them is important. Thus, this work facilitates and adds to our understanding of these important biases.
在过去的几十年中，混杂和选择偏倚的定义和概念化已经发展。随着可交换性概念的发展，取得了一个重要的进展。例如，如果可交换性成立，则可以比较未暴露组的疾病风险与暴露组的风险，以估计因果效应。另一个进展是使用因果图来总结因果关系，并促进识别可能表明偏倚的因果模式，包括混杂和选择偏倚。虽然它们密切相关，但可交换性是在反事实模型框架中定义的，而混杂路径是在因果图框架中定义的。此外，这些概念之间的精确关系尚未得到充分描述。在这里，我们总结了这些概念的定义和当前观点。我们展示了偏差、可交换性和有偏路径如何相互关联，并为关键结果提供了依据。例如，我们表明，没有有偏路径意味着可交换性，但如果没有附加假设（例如忠实性），则反之不一定成立。预期会出现紧密联系。然而，混杂、选择偏倚和可交换性是基本概念，因此对它们之间的联系进行全面总结和明确论证非常重要。因此，这项工作有助于我们理解这些重要的偏倚。
