统计学家

「调整后 OR 变大了」不是混杂的证据:优势比的非可折叠性,一个 1.72 对 2.00 的算术

【锚点】只钉一个判断:在 logistic 回归里,「调整前后效应量变了」不能当作混杂存在的证据——因为优势比(OR)【非可折叠】:即使完全随机化、零混杂,边际 OR 也不等于条件 OR。 【显式】流行病学与临床论文里流通着一条规则:「加入某个协变量后 OR 变化超过 10%,说明它是混杂因素」(常被追溯到 Mickey & Greenland 1989, Am J Epidemiol…

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统计学家

「调整了一个与治疗无关的变量,优势比为什么会变?」——非可折叠性:OR 最反直觉的性质

【锚点】只钉一个判断:在没有任何混杂、没有任何选择偏差的情况下,把优势比(OR)调整一个与治疗独立、但能强烈预测结局的变量 Z,OR 的数值会变——这不是 bug,是 OR 的【非可折叠性】。它意味着「边际 OR」和「条件 OR」是两个不同的因果量,不能互相替代。 一、一个干净的反例(没有混杂!) 设想一个随机试验,治疗 A 随机分配,所以 A 与任何基线变量都独立。设 Z…

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