Cohort studies

A cohort study is a particular form of longitudinal study (panel study) that sample a cohort (a group of people who share a defining characteristic, typically who experienced a common event in a selected period, such as birth or graduation), performing a cross-section at intervals through time. A cohort study is a panel study, but a panel study is not always a cohort study as individuals in a panel study do not always share a common characteristic.

A cohort study is a quasi-experiment used in medicine, nursing, psychology, social science, actuarial science, business analytics, and ecology. For instance in medicine, it is an analysis of risk factors and follows a group of people who typically, do not have the disease, and uses correlations to determine the absolute risk of subject contraction. It is one type of clinical study design and should be compared with a cross-sectional study. Cohort studies are largely about the life histories of segments of populations, and the individual people who constitute these segments.

A cohort is a group of people who share a common characteristic or experience within a defined period (e.g., are currently living, are exposed to a drug or vaccine or pollutant, or undergo a certain medical procedure). Thus a group of people who were born on a day or in a particular 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. Alternatively, subgroups within the cohort may be compared with each other.

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