What is a characteristic of a case-control study?

A case-control study is defined by its focus on comparing individuals who have a specific condition or outcome (the cases) to those who do not have the condition (the controls). One of the key characteristics that differentiate this type of study is its retrospective nature; it looks back in time to determine if there were any differences in exposure to potential risk factors between the two groups.

In this context, the comparison of past exposure between cases and controls is central to understanding whether certain exposures are associated with the outcome of interest. This method is particularly valuable in identifying risk factors for diseases that are relatively rare or when the outcome has already occurred, allowing researchers to draw associations based on historical exposure data.

The other options do not accurately describe case-control studies. For instance, case-control studies are not typically preventive studies, nor do they focus on future outcomes, which are characteristics more aligned with cohort studies. Additionally, they do not necessarily require large populations as they can be effectively conducted with smaller, well-defined groups based on the presence or absence of the condition being studied.