What is a "cohort" in epidemiology?

Question

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Answer 1

A well-defined group of people who have had a common experience or exposure, who are then followed up for the incidence of new diseases or events, as in a cohort or prospective study.

In epidemiology, the term cohort is defined as a group of people who share a common characteristic or experience within a defined time period (e.g., age, occupation, exposure to a drug or a vaccine, insured persons etc.). Thus a group of people who were born on a day or in a particular time period, say 1948, form a birth cohort. The comparison group may be the general population from which the cohort is drawn, or it may be another cohort of persons thought to have had little or no exposure to the substance under investigation, but otherwise similar.

Some cohort studies track a group of children from their birth, and record a wide range of information (exposures) about them. The value of a cohort study depends on the researchers' capacity to stay in touch with all members of the cohort. Some of these studies have continued for decades. An example of a cohort study that has been going on for more than 50 years is the Framingham Heart Study.

Answer 2

http://en.wikipedia.org/wiki/Cohort