Definition
An observational study draws inferences from a sample to population where the independent variable is not under the control of the researcher.
Types
Case-Control Study
Definition
A case-control study is a retrospective study that compares two groups of people: those with a specific outcome (cases) and similar people without the outcome (control)
Examples
Suppose that researchers want to study the relationship between smoking and lung cancer. They identify 100 lung cancer patients (cases) and 100 matched individuals without lung cancer (controls). They then collect data on past smoking habits for both groups and compare the prevalence of smoking between cases and controls.
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Cohort Study
Definition
A cohort study is a prospective study that follows a group of individuals (cohort) over time to determine the incidence of a specific outcome.
Examples
Suppose that researchers want to study the relationship between smoking and lung cancer. They follow a group of 10,000 people for 20 years, comparing smokers to non-smokers to determine the incidence of lung cancer.
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Cross-Sectional Study
Definition
A cross-sectional study analyzes data from a population at a specific point in time. It provides a snapshot of the prevalence in a population
Examples
Suppose that researchers want to study the relationship between smoking and lung cancer. They survey 1,000 people in a city, collecting data on their current smoking habits and presence of lung cancer.
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