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:

  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
     main result

  2. Non-causal explanation

  3. Positive features

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

  5. Comparison with other evidence
     plausibility and coherence