| The strength of the association | The greater the magnitude of the association the greater the likelihood that it is causal |
| Consistency | If the association is observed at different times, places and by different researchers it is more credible |
| Specificity | The more specific the disease and the groups of people affected the greater the likelihood of causality |
| Temporal relation | Does the suspected cause precede the disease |
| Biological gradient | Is there a dose–response type relation |
| Biological plausibility | Do the findings fit with plausible biological and disease mechanisms |
| Coherence of the evidence | The cause and effect interpretation should fit with other known facts regarding the natural history and biology of the disease |
| Prevention | Does avoidance or removal of the cause decrease the incidence of the disease |
| Reasoning by analogy | Does the evidence mirror or match another cause and effect relation |