The gold standard of scientific evidence is the randomised controlled trial, preferably one with a lot of people and held over a long time.

国际上科学证据的标准是由随机对照实验得出的结果，尤其是那些有很多人参与又经过很长时间的实验。

youdao

The researchers at Harvard couldn't run a randomised controlled trial where half the participants ate burgers for two decades and the other half didn't, but they could use statistical techniques as the next best thing.

BBC: Red meat: What is a 13% increase in the risk of death?