Causality

Lots of things can be associated with outcomes that we wish to study but few of them are meaningful causes.

In Epidemiology, the following criteria due to Bradford-Hill are used as evidence to support a causal association:

1. Plausibility (reasonable pathway to link outcome to exposure)

2. Consistency (same results if repeat in different time, place person)

3. Temporality (exposure precedes outcome)

4. Strength (with or without a dose response relationship)

5. Specificity (causal factor relates only to the outcome in question - not often)

6. Change in risk factor (i.e. incidence drops if risk factor removed)

Elwood's criteria are a modern extension of this concept:

1. Descriptive evidence
    exposure or intervention
    design
    population
    main result

2. Non-causal explanation
    chance
    bias
    confounding

3. Positive features
    time
    strength
    dose-response
    consistency
    specificity

4. Generalisability
    to eligible population
    to source population
    to other populations

5. Comparison with other evidence
    consistency
    specificity
    plausibility and coherence