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A cohort is a subpopulation of population members who share a common property within a defined time period.



    • QUOTE:A cohort is a group of people who share a common characteristic or experience within a defined period (e.g., are born, 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.

    • QUOTE:In statistics and demography, a cohort is a group of subjects who have shared a particular time together during a particular time span[1] (e.g., people born in Europe between 1918 and 1939; survivors of an aircrash; truck drivers who smoked between age 30 and 40). Cohorts may be tracked over extended periods in a cohort study. The cohort can be modified by censoring, i.e. excluding certain individuals from statistical calculations relating to time periods (e.g. after death) when their data would contaminate the conclusions.

      The term cohort can also be used where membership of a group is defined by some factor other than a time-based one: for example, where a study covers workers in many buildings, a cohort might consist of the people who work in a given building.[2]

      Demography often contrasts cohort perspectives and period perspectives. For instance, the total cohort fertility rate is an index of the average completed family size for cohorts of women, but since it can only be known for women who have finished child-bearing, it cannot be measured for currently fertile women. It can be calculated as the sum of the cohort's age-specific fertility rates that obtain as it ages through time. In contrast, the total period fertility rate uses current age-specific fertility rates to calculate the completed family size for a notional woman and man were she to experience these fertility rates through her life. In life table, a cohort refers to a specific rate of fecundity.

  1. "BLS Information". Glossary. U.S. Bureau of Labor Statistics Division of Information Services. February 28, 2008. Retrieved 2009-05-05. 
  2. Dodge, Y. (2003) The Oxford Dictionary of Statistical Terms, OUP. ISBN 0-19-920613-9


  • WordNet.
    • a company of companions or supporters
    • a band of warriors (originally a unit of a Roman Legion)
    • age group: a group of people having approximately the same age

  • US National Institute of Health. “IUPAC Glossary of Terms Used in Toxicology."
    • QUOTE: cohort: Component of the population born during a particular period and identified by period of birth so that its characteristics (such as causes of death and numbers still living) can be ascertained as it enters successive time and age periods. The term “cohort” has broadened to describe any designated group of persons followed or traced over a period of time, as in the term cohort study (prospective study).