In a cohort study, what characteristic do the participants share?

In a cohort study, participants share a specific characteristic that differentiates them based on a certain variable, which is often termed as an exposure. This characteristic can relate to lifestyle factors, risk factors, or any other variable of interest that the researchers aim to study. By selecting participants who differ by this variable, researchers can observe how these differences influence the outcomes over time. This design allows for the examination of associations between exposures and outcomes, making it a valuable tool in epidemiology for understanding the impact of various factors on health.

The other options do not accurately represent the nature of a cohort study. For instance, not all participants in a cohort study will have a similar outcome; the goal is often to study the variability in outcomes resulting from the exposure. Age can be a factor in certain cohort studies, but it is not a requirement that all participants be of the same age. Gender-specific studies can exist, but cohort studies are not limited to one gender; they can include diverse populations to capture a range of outcomes related to different exposures.