觀察性研究跟 RCT 在副作用/危險的結果是一致的

要研究因果關係，只能用 RCT，不能用觀察性研究，因為後者無法排除干擾因子（造成暴露和結局的因子）的影響。但是 RCT 不能用來研究有害的暴露因子，而且其在治療所致副作用/危險的結果方面跟觀察性研究是一致的。


An empirical comparison of the harmful effects for randomized controlled trials and non-randomized studies of interventions 23

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10070801/

RCT 的統計檢定力（樣本數）是依據效果（主要終點）計算的，因此針對副作用/危險的樣本數是不足的。本研究發現觀察性研究跟 RCT 在副作用/危險的結果是一致的。


Probability of adverse events that have not yet occurred: a statistical reminder 1995

https://www.bmj.com/content/311/7005/619

在 n 次試驗裏面，沒有一次有發生某事件，那麼會發生某事件的 95% 信賴區間是 0- 3/n（n>30）。假設在 1000 個受試者中，沒有人發生副作用，那麼該副作用發生的機率是 0-3/1000。假設在 1000 個受試者中，有 1 個人發生副作用，那麼該副作用發生的機率是 0-5.6/1000。

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