KEY

Investigator at beginning of study

? To be determined

At the beginning of a prospective cohort study, the investigator is aware of a group of individuals, some of whom have been exposed to a hazard. All members of the cohort will be followed over time to see if those exposed and those unexposed have different disease experiences.

For example, a public health department may be informed of the exposure of a portion of a school class to an individual with an active case of a communicable disease in the course of a field trip. The entire class (the cohort) would be observed over time to identify any cases of disease that arise, and any difference in disease rate between the two groups.