6: Causality Flashcards
Define
Cause
Causality
Association
Cause
something that brings about an effect or a result
Causality
the realtion between a cause and its effect
Association
any statistical relationship between 2 variables. association does not mean causality
Deterministic vs probabilistic theory
Deterministic cause
A must always be followed by B
Probabilistic cause
A causally increases the risk for B
Causes can be classified as…
multiple factors
in most diseases multiple factors are needed to cause a disease
sufficient
cause always induces disease but there may be other set of causes that can cause disease
necessary
without the cause, the disease never occurs
How to infer causality?
First, is there an association?
If yes, that isnt enough:
a)Henle-Koch postulates:
organism must be present in every case of disease, isolated grown in culture, cultured must causes disease in new human, ….
-> limitations
b)multiple factors are needed to cause disease
c) Bradford-Hill criteria
Bradford-Hill criteria part 1
Is there any other way of explaining the facts we study ?
-> 8 criteria
Temporarily
Does the cause precede the effect?
- first exposure, then effect
Strength of association
- indication for causality if RR/IR/HR far away from 1, otherwise unmeasured factors can be responsible for false effects, if false effects are big they should be obvoius (cofounding)
Dose-response relationship
the higher the exposure, the more probable the event
Replication of findings
repeated observation in different populations, meta analysis
Pitfall: statistical significance does not equal strength of association
Bradford Hill criteria part 2
Biological plausability
postulated association should be based on biological model
Reversibility
Deletion of the cause should lower disease probability
Specificity
specific exposure causes one disease and no other exposure causes this diesease
Analogy
Are there cause-effect relationship for a similar exposure or disease which are already established
