Dr Dharmabalan posted this note on definition of the study types: This is a useful note for medical students and junior doctors.

COHORT STUDY
Cohort : a group of persons sharing a particular statistical or demographic characteristic

Cohort studies are a type of medical research used to investigate the causes of disease, establishing links between risk factors and health outcomes.

Cohort studies are usually forward-looking – that is, they are “prospective” studies, or planned in advance and carried out over a future period of time.

Retrospective cohort studies look at data that already exists and tries to identify risk factors for particular conditions.

In a prospective cohort study, researchers first raise a research question, forming a hypothesis about the potential causes of a disease. The researchers then observe a group of people, the cohort, over a period of time (often several years), collecting data that may be relevant to the disease. This allows the researchers to detect any changes in health in relation to the potential risk factors they have identified.

Cohort studies are observational – the researchers simply observe what happens, without applying any intervention themselves. Conversely, experimental studies, such as RCTs, (randomized controlled trials), involve an intervention by the scientists – the introduction of a drug.

The cohort study design is the best available scientific method for measuring the effects of a suspected risk factor.