A cohort study tracks two or more groups forward from exposure to outcome Steps

# A cohort study tracks two or more groups forward from

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A cohort study tracks two or more groups forward from exposure to outcome.
Steps: 1 . Select a sample from the population 2. Measure exposure variables (risk factor present or absent) 3. Follow-up the cohort 4. Measure outcome variables (disease present or absent) Design of Cohort study
a . Descriptive Estimate the incidence or natural history of a disease or some other outcome. Evaluate new therapies and prevention Evaluate screening procedures and determine a prognosis b. Analytic Analyze associations between risk factors and outcomes Goals
time Exposure Study starts Disease occurrence Prospective cohort study Exposure Disease occurrence time Study starts
Retrospective cohort studies Exposure time Disease occurrence Study starts Assembly of the cohort, baseline measurements, follow-up and occurrence of outcomes all happened in the past
Retrospective versus prospective cohort studies exposure to the risk factor and subsequent health outcomes are observed after the beginning of the study. takes a long time, and can collect reliable information it utilizes information on prior exposure to the risk factor and subsequent disease status. that all events under study have already occurred, and conclusion can be drawn more rapidly.
COHORT STUDIES 50% 50% 10% 90% exposure (+) (+) (-) (-) (+) (+) (-) (-) Disease Disease Basic Idea Basic Idea : : See if those See if those with with the risk the risk factor develop factor develop more more disease than those disease than those without the risk factor without the risk factor
Famous Example
Framinham heart study Beginning in 1950, a sample of 6500 individuals aged 30-59 years was chosen from a total population of approximately 10,000 people in that age group. 5100 subjects with no cardiovascular agreed to participate in the study.
1948- Present Each subject was examined at the beginning of the study and was reexamined every 2 years thereafter.
health outcome Framinham heart study Study begins
Exposur and outcome identified subjects who had: The unexposed group: people without the risk factors of interest . Elevated blood pressure Elevated serum cholesterol smoked Followed over 35 years to identify subjects Suffered a myocardial infarction, stroke and other adverse cardiovascular event.
MAJOR MOMENT IN THE FRAMINGHAM HEART STUDY 1948 Framingham heart study begins 1956 Findings on progression of rheumatic heart disease reported 1957

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