Disease cohort (non-aetiological studies)Īim is to compare the outcome of different groups of patients who have suffered from a specific disease and follow them to find out what the outcome will be. Numbers must be large enough so that an appreciable number of people in either group will succumb to the disease.Ģ. Disease free cohort (aetiological studies)Īim is to see if incidence of the disease is greater in people exposed to a suspected cause than in those not exposed. Case control studies trace backwards from outcome to exposure. Cohorts track people forward in time from exposure to outcome. Historical cohort studies should not be confused with case-control studies (also retrospective). Sometimes referred to as historical cohort studies, they offer the advantage of speed and low cost compared to a prospective cohort. A retrospective design is effective for diseases with a long development time. Prospective design allows exposure to risk factors to be assessed directly and confounding variables to be considered. A cohort can sometimes be used to mean a group of individuals followed over a period of time to examine the cause or progress of disease (or physiological variable) or to chart its long term effects.Ĭohort studies can be designed to be prospective or retrospective. It is worth noting that the term 'cohort' is also used in relation to a group of people who share a similar experience at a point in time, e.g. In a cohort study, precise choice of cohort depends on the nature of disease under investigation. Cohorts look at causes and natural history of diseases and are also useful for examining prognosis of people who already have the disease. If the exposed group has a higher or lower frequency of an outcome than the unexposed, then an association between exposure and outcome is evident. They compare the experience of one group exposed to a factor (exposed group) with that of the other which was not exposed to the factor (control group). Cohort studies follow up two or more groups from exposure to outcome. A cohort study is an analytical observation study, i.e. Unlike experimental studies, observational studies do not look at the effectiveness of an intervention. Observational studies differ from experimental studies in that the researcher does not control the assignment of people to groups.
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