Hill’s criteria for Epidemiology Studies

Sir Richard Doll (1912-2005), the father of epidemiological studies on tobacco and disease and his mentor Sir Austin Bradford Hill (1987-1991) established the criteria for case controlled studies in epidemiology.

Hill's explicit statement that cause-effect decisions cannot be based on a set of rules. Overlooked are Hill's important lessons about how to make decisions based on epidemiologic evidence. He advised epidemiologists to avoid over-emphasizing statistical significance testing, given the observation that systematic error is often greater than random error. His compelling and intuitive examples point out the need to consider costs and benefits when making decisions about health-promoting interventions  

• Statistical significance should not be mistaken for evidence of a substantial association.

• Association does not prove causation (other evidence must be considered).

• Precision should not be mistaken for validity (non-random errors exist).

• Evidence (or belief) that there is a causal relationship is not sufficient to suggest action should be taken.

• Uncertainty about whether there is a causal relationship (or even an association) is not sufficient to suggest action should not be taken.

In 1953: Sir Richard Doll establishes a correlation between actively smoking cigarettes and lung cancer risk. However, over subsequent decades,  Doll changed his views in 2005, in a IARC scientific working group, convened to review evidence relating tobacco smoking and cancer, Doll finally admitted: "It does look as if it's the cancers that are principally caused by hormones that are not affected by smoking. Most of the other cancers throughout the body are induced by exposure to chemicals, often environmental ones”.