wait decades to get a result.</p>
<p>Fortunately, around 1960, a researcher at the US National Institutes of Health, Jerome Cornfield, was able to show mathematically that the strength of the association between smoking and cancer ruled out any genetic mechanism. Cornfield’s work was a key step in developing a new area in statistics: “<strong>causal inference</strong>.”</p>
<p>Causal inference is not about proving that one thing causes another but about formal ways to say something about how the world