To determine whether there is a cause-effect relationship, the following criteria need to be evaluated:
1. STRENGTH OF ASSOCIATION:
What is the relative risk or odds ratio for the exposure and the disease? A larger ratio means that the exposure more likely caused the disease. For example,if a study that you found on the internet states that individuals who smoked were 10 times more likely to develop lung cancer than individuals who did not, and they are referring to has an odds ratio or relative risk that is equal to 10. Recall that an odds ratio or relative risk that is equal to one means there is no difference.
2. DOSE-RESPONSE RELATIONSHIP:
According to studies (such as those on the internet), does increasing levels of exposure to the factor (such as smoking) result in a corresponding rise in disease? If there is a corresponding rise in occurrence of disease with increasing levels of exposure to a factor, it is more likely that there is a cause-effect relationship?
3. CONSISTENCY OF ASSOCIATION:
Has there been many studies indicating that there is an association between the exposure and the disease? If the same association is found using different study designs, different populations, and different settings, there is a consistency of association and it is more likely that there is a cause-effect relationship.
4. TEMPORALLY CORRECT ASSOCIATION:
Does the exposure occur before the onset of disease? The exposure must precede onset of illness.
5. BIOLOGICAL PLAUSIBILITY:
Does the association between the exposure and the disease make sense? Why? The association between the exposure and the disease must be plausible in terms of current knowledge about the factor and the disease.