Final answer:
Epidemiologists compare two groups using incidence rates: those exposed to a risk factor and those not exposed, to evaluate the association between the exposure and disease occurrence.
Step-by-step explanation:
When using incidence rates, epidemiologists typically compare two distinct groups: those who have been exposed to a certain risk factor and those who have not. The comparison aims to discern whether there is an association between the exposure and the occurrence of a health-related event such as a disease. This is fundamental in epidemiological studies to determine potential causes and to estimate the risk of developing the disease in question.
To illustrate, if a study is investigating the relationship between smoking and lung cancer, researchers would compare the incidence rate of lung cancer among smokers (exposed group) to the incidence rate of lung cancer among non-smokers (unexposed group). They often use a 2 x 2 table to organize this data and calculate the relative risk, which indicates the strength of the association between smoking and lung cancer.