Bradford Hill Criteria

Bradford Hill Criteria

Determing causality is difficult, in part because the word causality has multiple meanings.

  1. Prediction (aka Sufficiency). X causes Y to happen in the sense that if I do X Y happens more than I would expect by chance.
  2. Explanation (aka Necessity). X causes Y to happen in the sense that Y cannot happen without X. This suggests that X is integral to Y’s realization.

In graduate school, I remember being taught that one can say that one thing causes another only if both things are true. Requiring (1) and (2) to both be true is equivalent to enforcing a biconditional.

$$ \begin{aligned} X &\rightarrow Y\\ \neg X &\rightarrow \neg Y \quad \textrm{by contrapositive } Y \rightarrow X
& \therefore X \leftrightarrow Y \end{aligned} $$

The notation brings out a limitation of this reasoning. It is first-order logic and brooks no conditionality.

Bradford-Hill Criteria

The Bradford-Hill Criteria are guidelines that approximate a second-order logic generalization of the above formalism.

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