Table 1.

Bradford-Hill Criteria

Biological Plausibility	It is easier to accept an association as causal when there is a rational and theoretical basis for such a conclusion.
Experimental Findings	Related research that is based on experiments will make a causal inference more plausible.
Dose Response Relationship	There should be a direct relationship between the risk factor (i.e., exposure) and the people’s status on the disease variable (i.e. outcome).
Temporality	It is logically necessary for a cause to precede an effect in time.
Strength of Association	The stronger the relationship between the independent variable and the dependent variable, the less likely it is that the relationship is due to an extraneous variable.
Consistency	Multiple, observations of an association, with different people under different circumstances and will different measurement instruments increase the credibility of a finding.
Specificity	In the ideal situation, the effect only has one cause. There is added credibility to a causal claim when an outcome is best predicted by one primary factor.
Coherence	A cause-and-effect interpretation for an association is clearest when it does not conflict with what is known about the variables under study and when there are no plausible competing theories or rival hypotheses. The association must me coherent with other knowledge.
Analogy	Sometimes a commonly accepted phenomenon is one area can be applied to another area.