COHORT STUDYDr. Muhammad Tareque HasanTeaching Assistant Department of EpidemiologyBUHS1
Concept of cohort•The word cohort is derived from the Latin “cohorts” meaning an enclosure, company, or crowd. •In Roman times a cohort was a body of 300–600 infantry. •In epidemiological terms the cohort is a group of people with something in common, usually an exposure or involvement in a defined population group.2
Definition•Cohort study is a type of analytical study which is undertaken to obtain additional evidence to refute or support existence of association between suspected cause and diseases. •Other names of cohort study are Longitudinal study, Incidence study and forward looking study3
Features of cohort studies•Cohorts are identified prior to appearance of disease under investigation•The study groups are observed over a period of time to determine the frequency of disease among them•The study proceeds from cause to effects4
Design of Cohort StudyEXPOSEDNOT EXPOSEDDISEASEDEVELOPSDISEASE DOES NOT DEVELOPDISEASE DOES NOT DEVELOPDISEASE DEVELOPS5
Steps of Cohort Study1•Selection of study population2•Obtaining Data on exposure3•Selection of comparison group4•Follow up5•Analysis6
1. Selection of study subjectsThe usual procedure is to locate or identify the cohort, which may be a total population in an area or sample thereof. Cohort can be:•community cohort of specific age and sex;•exposure cohort e.g. radiologists, smokers, users of oral contraceptives;•birth cohort e.g. school entrants;•occupational cohort e.g. miners, military personnel;•marriage cohort;•diagnosed or treated cohort, e.g. cases treated with radiotherapy, surgery, hormonal treatment.