Bradford Hill criteria

The Bradford Hill criteria, otherwise known as Hill's criteria for causation, are a group of minimal conditions necessary to provide adequate evidence of a causal relationship between an incidence and a consequence, established by the English epidemiologist Sir Austin Bradford Hill (1897–1991) in 1965.

The list of the criteria is as follows:
 * 1) Strength of association (relative risk, odds ratio)
 * 2) Consistency
 * 3) Specificity
 * 4) Temporal relationship (temporality) - not heuristic; factually necessary for cause to precede consequence
 * 5) Biological gradient (dose-response relationship)
 * 6) Plausibility (biological plausibility)
 * 7) Coherence
 * 8) Experiment (reversibility)
 * 9) Analogy (consideration of alternate explanations)

Debate in modern epidemiology
Bradford Hill's criteria are still widely accepted in the modern era as a logical structure for investigating and defining causality in epidemiological study. However, their method of application is debated. For example, using a counterfactual consideration as the basis for applying each criterion is one perspective. An operational reformulation of the criteria has been recently proposed in the context of evidence based medicine, subdividing them into three categories: direct, mechanistic and parallel evidence, expected to complement each other.

Arguments against the use of Bradford Hill criteria as exclusive considerations in proving causality also exist. Some argue that the basic mechanism of proving causality is not in applying specific criteria - whether those of Bradford Hill or counterfactual argument - but in scientific common sense deduction. Others also argue that the specific study from which data has been produced is important, and while the Bradford-Hill criteria may be applied to test causality in these scenarios, the study type may rule out deducing or inducing causality, and the criteria are only of use in inferring the best explanation of this data.

Debate over the scope of application of the criteria includes whether they can be applied to social sciences. The argument proposed in this line of thought is that when considering the motives behind defining causality, the Bradford Hill criteria are important to apply to complex systems such as health sciences because they are useful in prediction models where a consequence is sought; explanation models as to why causation occurred are deduced less easily from Bradford Hill criteria as the instigation of causation, rather than the consequence, is needed for these models.