Kohort

A kohort is a term used in epidemiology, demography, and social sciences to describe a group of individuals distinguished by a shared temporal characteristic, most commonly birth year or enrollment period. The concept originates from the French cohorte and Latin cohors, and in German-language usage the term Kohort is common. In research, a cohort is followed over time to observe outcomes, exposures, or transitions, allowing estimation of incidence and the assessment of associations between exposures and diseases.

Cohort studies are classified as prospective when outcomes have not yet occurred at the start of follow-up, and retrospective (historical) when records are used to reconstruct past exposure and outcome data. Key measures include cumulative incidence, incidence rate, relative risk (risk ratio), and hazard ratio. Cohorts enable investigation of rare or long-latency outcomes and help control for confounding through design and analysis, though they require careful handling of loss to follow-up and potential selection bias.

In demography, a birth cohort (for example, people born in 1980–1985) is studied to understand how the shared life experiences of that generation influence health, education, and economic outcomes. The concept of a cohort effect describes systematic differences between cohorts arising from social, environmental, or policy changes rather than aging alone.

Applications extend to epidemiology, public health planning, sociology, and market research, where cohort analysis tracks users or customers over time to identify behavioral patterns and lifecycle effects.