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Cohort studies are classified under the non-experimental type of studies , which are observational by default .A cohort study follows people as groups, two or more, from exposure to outcome [2, 8].
The term “cohort” originates from Latin “cohors” .
A term that was used in the military back in Roman times, which referred to a unit that is comprised of 300–600 men, of which each 10 cohorts were named a legion .
Due to the design of cohort studies, and since temporal sequence is present, both incidence rate and cumulative incidence can be calculated [2, 8, 20, 21, 22].
They also allow for the measurement of relative risk (RR) [2, 8, 23], hazard ratio , and attributable risk [8, 23].
In the third we go over examples of prospective studies in the medical field.
For each, an overview of the study design is given, along with a random selection of study findings/impact, strengths and weaknesses.In retrospective studies the odds ratio provides an estimate of relative risk.You should take special care to avoid sources of bias and confounding in retrospective studies.The two groups would be categorized based on their exposure status to “exposed” and “unexposed” [4, 9, 10].If there were multiple groups then these would be categorized either by the type or level of exposure .In the second we focus on the design of cohort studies, mainly its prospective aspect, and the distinguishing features from the retrospective type.The section also covers the essential characteristics of a cohort study design and its varied applications in medical research.Prospective studies usually have fewer potential sources of bias and confounding than retrospective studies.A retrospective study looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is established at the start of the study.For this reason, retrospective investigations are often criticised.If the outcome of interest is uncommon, however, the size of prospective investigation required to estimate relative risk is often too large to be feasible.