Causality
Many factors can be associated with outcomes but few are meaningful causes.
In Epidemiology, the following criteria due to Bradford-Hill are used as evidence to support a causal association:
- Plausibility (reasonable pathway to link outcome to exposure)
- Consistency (same results if repeat in different time, place person)
- Temporality (exposure precedes outcome)
- Strength (with or without a dose response relationship)
- Specificity (causal factor relates only to the outcome in question - not often)
- Change in risk factor (i.e. incidence drops if risk factor removed)
Elwood's criteria are a modern extension of this concept:
-
Descriptive evidence
exposure or intervention
design
population
main result -
Non-causal explanation
chance
bias
confounding -
Positive features
time
strength
dose-response
consistency
specificity -
Generalisability
to eligible population
to source population
to other populations -
Comparison with other evidence
consistency
specificity
plausibility and coherence