Criteria for Causation

Hill's Criteria Example

In the following example, we apply Hill's criteria to the case of smoking and lung cancer.

Strength of Association - The lung cancer rate for smokers was quite a bit higher than for nonsmokers (e.g., one study estimated that smokers are about 35% more likely than nonsmokers to get lung cancer).
Temporality - Smoking precedes the onset of lung cancer.
Consistency - Different methods (e.g., prospective and retrospective studies) produced the same result. The relationship also appeared for different kinds of people (e.g., males and females).
Plausibility - Biological theory of smoking causing tissue damage which over time results in cancer in the cells was a highly plausible explanation.
Coherence - The conclusion (that smoking causes lung cancer) "made sense" given the current knowledge about the biology and history of the disease.
Specificity in the causes - Lung cancer is best predicted from the incidence of smoking.
Dose Response Relationship - Data showed a positive, linear relationship between the amount smoked and the incidence of lung cancer.
Experimental Evidence - Tar painted on laboratory rabbits' ears was shown to produce cancer in the ear tissue over time. Hence, it was clear that carcinogens were present in tobacco tar.
Analogy - Induced smoking with laboratory rats showed a causal relationship. It, therefore, was not a great jump for scientists to apply this to humans.

Adapted from www.cdc.gov/excite and http://www.southalabama.edu/coe/bset/johnson/bonus/Ch11/Causality%20criteria.pdf

Although there are a total of nine criteria for establishing causality, some are more commonly accepted than others. Those that are more commonly accepted are: strength of the association, temporality, consistency, dose response relationship, and plausibility.

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