Causal Criteria

Question 1

Temporality

Answer 1

A cause must precede an effect; the only necessary criterion for causality

Question 2

Consistency

Answer 2

Replication of finding by different investigators (different studies); at different times, in different places, with different methods, convincingly explain different results; replication under similar circumstances

Question 3

Strength of association

Answer 3

Strong associations are less likely to be a result of chance, bias, or other etiologic factors; based on quantitative evidence (odds ratio, risk ratio)

Question 4

Biological gradient

Answer 4

The greater the exposure to the risk factor, the higher the risk of the outcome; dose response relationship

Example: light smokers get lung CA at a rate intermediate between heavy smoker and non smokers

Question 5

Coherence

Answer 5

Evidence does not conflict with known facts (known biology and natural history of disease)

Question 6

Plausibility

Answer 6

A biologically plausible mechanism exists to explain why the relationship between exposure and outcome would be expected

Question 7

Experiment

Answer 7

A demonstration that, under controlled conditions, changing the exposure causes outcome

Question 8

Analogy

Answer 8

Evidence is similar to previously established causal relationship

Question 9

Specificity of the association

Answer 9

Disease is associated with one rather than many exposures; not appropriate for chronic disease