Department of Epidemiology, UNC Gillings School of Global Public Health, Chapel Hill, NC, USA.
Int J Epidemiol. 2010 Apr;39(2):417-20. doi: 10.1093/ije/dyp334. Epub 2009 Nov 19.
That conditioning on a common effect of exposure and outcome may cause selection, or collider-stratification, bias is not intuitive. We provide two hypothetical examples to convey concepts underlying bias due to conditioning on a collider. In the first example, fever is a common effect of influenza and consumption of a tainted egg-salad sandwich. In the second example, case-status is a common effect of a genotype and an environmental factor. In both examples, conditioning on the common effect imparts an association between two otherwise independent variables; we call this selection bias.
在暴露和结局的共同效应上进行条件分析可能导致选择偏倚或混杂-分层偏倚，这并不直观。我们提供了两个假设性的例子，以传达由于在混杂因素上进行条件分析而导致偏倚的基本概念。在第一个例子中，发烧是流感和食用受污染的鸡蛋沙拉三明治的共同效应。在第二个例子中，病例状态是基因型和环境因素的共同效应。在这两个例子中，在共同效应上进行条件分析赋予了两个原本独立的变量之间的关联；我们称之为选择偏倚。
