[A. B. Hill (1897–1991), British medical statistician] A set of nine criteria used to determine the strength of an association between a disease and its supposed causative agent. They form the basis of modern medical and dental epidemiological research.
The nine Bradford Hill criteria
Strength of association
The stronger the association, the more likely it is that the relation is causal.
Exposure always precedes the outcome.
The association is consistent when results are replicated with different people under different circumstances and with different measurement instruments.
It is easier to accept an association as causal when there is a rational and theoretical basis for such a conclusion.
The association should be compatible with existing theory, hypotheses, and knowledge.
In the ideal situation, the effect has only one cause.
Dose response relationship
An increasing amount of exposure increases the risk.
Any related research that is based on experiments will make a causal inference more plausible.
Sometimes a commonly accepted phenomenon in one area can be applied to another area.