In epidemiologic research, what is compared in a case-control study?

In a case-control study, the primary focus is on comparing affected individuals, known as cases, with unaffected individuals, referred to as controls. The aim is to identify and evaluate factors that may contribute to the presence of a specific condition or outcome. By looking at these two groups, researchers can ascertain whether particular exposures or characteristics are more prevalent in the cases compared to the controls, which helps to uncover potential associations.

This design is particularly powerful for studying rare conditions, as it allows for the efficient use of resources by selecting individuals who have the disease and comparing them to those who do not. The depth of information gained from this comparison can reveal insights about risk factors and contribute to understanding the etiology of diseases.

The other options describe different forms of comparisons that might be relevant in other types of studies, but they do not accurately reflect the structure and purpose of a case-control study. Each of those comparisons may be fruitful in other research contexts but are not suited to the case-control design method.