Cohort Study

General outline on Cohort Study:- • Definition of cohort study A type of analytic study which groups of individuals defined on the basis of their exposure status is followed to assess the occurrence of disease. • What is Cohort? Cohort is defined as a group of people who share a common characteristic or experience within a defined time period. Example; Birth cohort, Occupation cohort, Exposure cohort, Marriage cohort, etc. • Types of Cohort Studies 1. Prospective Cohort Studies: Concurrent cohort: A prospective cohort study is one in which the outcome has not yet occurred at the time the investigation begins in the present and continue into future. 2. Retrospective Cohort Study: A retrospective or historical cohort study is one in which the outcomes have all occurred before the start of investigation, the investigator goes back in time. 3 Retro-Prospective Study In this type of study, both the retrospective and Prospective elements are combined. The cohort is identified from past records and it’s assessed of data for outcome. The same cohort is followed up prospectively into future for further assessment of outcomes. • General consideration while selection of cohorts o Both the cohorts are free of the disease. o Both the groups should equally susceptible to disease o Both the groups should be comparable o Diagnostic and eligibility criteria for the disease should be defined well in advance. • Steps of carrying out a cohorts study 1. Selection of Study subjects. 2. Obtaining data on exposures. 3. Selection of comparison groups. 4. Follow-up 5. Analysis and interpretation