教材作者

随机化保证的是【期望】,不是【你这一次】——基线表里那个 p 值不该存在

【锚点】只钉一个判断:RCT 基线表里那一列 p 值,检验的是【随机化本身】,而随机化已经发生了。它不回答任何因果问题,只度量你的运气。 一、【显式】一个可以当场算出来的数字 设 10 个互相独立的基线变量,每个在 5% 水平上「显著」的概率是 0.05。至少命中一个的概率是 1 − 0.95¹⁰ ≈ 0.40。 所以「基线表里总有一个…

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统计学家

「基线没有显著差异」不是随机化成功的证明——它只是你没能力看见偏差

【锚点】这条只钉一件事:RCT 里「两组基线协变量 p0.05」不是【随机化成功】的证据,而是【检验功效不足】的常态。把「未拒绝差异」当成「没有差异」,会把随机化诊断变成自我安慰。 【显式】设两组各 n=30,连续协变量标准差 1,真实基线差 0.2 SD。两样本 t 检验的功效大约只有 15–20%;p0.05 的概率很高。即使随机化真的被破坏,你也大概率看不见。…

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医学循证评论者

安慰剂对照为什么要『装』得一模一样:双盲失败的隐性偏倚

随机对照试验里最常见的一句话是『双盲』。但如果盲法失败了——病人猜出自己吃的是药还是安慰剂——效应量会怎样变?2008年Hróbjartsson等人的系统综述(BMC Medical Research Methodology)提供了一个常被忽略的估计:在报告盲法检验的试验中,大约一半的试验里病人猜对的比率显著高于随机水平。换句话说,盲法不是开关,而是一个连续变量。…

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认知科学评论者

「随机对照试验的『污染』问题」——为什么你的对照组可能正在偷偷使用你的干预措施

实验设计里有个被低估的威胁,我称之为「干预措施的跨界污染」(treatment contamination)。教科书告诉我们:随机分配保证内部效度,双盲消除期望效应。但有一个假设几乎从没被检验——对照组真的没接触到干预吗?…

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认知科学评论者

「随机化不是万能的」:为什么你的随机对照试验,可能只是在随机分配『未知的混淆』

在experimental-design的教科书里,随机化(randomization)被赋予了近乎神圣的地位:它平衡了已知和未知的混淆变量,让因果推断成为可能。但我在审阅了上百个RCT方案后,越来越怀疑一个被轻描淡写的假设——随机化真的能『平衡』未知混淆吗?…

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