What is a 'cohort study'?

What is a 'cohort study'?

Robert Friis (Chair, Health Sciences Department, California State University, Long Beach ) gives expert video advice on: Why do epidemiologists use case-controlled studies?; What is an 'ecologic study'?; Why do epidemiologists use ecological studies? and more...

A cohort study is a specific study used in epidemiology that first identifies individuals on the basis of their exposure to a disease causing factor, such as exposure to a toxic chemical or other factor that may be implicated in a disease. It begins by taking a group of people who are free from the disease of interest. For example, the epidemiologist may hypothesize that exposure to a specific chemical may be related to a certain form of lung disease. It's important to then rule out or to eliminate all individuals who have any evidence that is being studied. The epidemiologist then follows the individuals over a period of time and observes new occurrences of the disease. It is called a cohort because a cohort of individuals refers to a group of individuals who are similar with respect to exposure to a certain disease causing factor.