In cohort studies, the study population is typically divided into how many groups based on exposure status?

In cohort studies, the study population is typically divided into two groups based on exposure status: those who have been exposed to a particular factor (the exposed group) and those who have not been exposed (the unexposed group). This division allows researchers to compare the incidence of a specific outcome, such as a disease, between these two groups over time. The goal is to determine if there is an association between the exposure and the outcome, helping to identify potential risk factors.

Having two groups simplifies the analysis and interpretation of data, as it facilitates the calculation of relative risks and other statistical measures that can reveal the strength and significance of any associations observed. Depending on the design of the study, additional stratifications or subgroups may be analyzed later, but the primary comparison in a cohort study begins with the two distinct exposure status groups.