Association or causation

Epidemiological studies can only show associations they cannot prove that a link is causative. Even in the bias free study with minimal confounding, a strong association does not mean that, for example, the presence of the risk factor has a direct biological link to the disease in question. There are several tests that can be used to increase the confidence that an association has biological meaning and needs to be considered. It is interesting always to differentiate factors that are on the ‘path’ to disease but not the underlying cause. The appropriateness of all these steps is dependent on the validity of the association.