BOX 4-2 Epidemiological Methods for Discovering Genetic Links to Disease

Case-control studies are retrospective observational studies in which investigators identify one group of patients with a specified outcome (cases) and another group without the specified outcome (controls). Investigators then compare the histories of the cases and the controls to determine the extent to which each had the possible risk factor being investigated.

Cohort studies are observational studies in which outcomes in a group of patients who possess the possible risk factor being tested (the cohort) are compared with outcomes in a control group of patients who do not possess the possible risk factor. For example, the occurrence of breast cancer would be compared between two groups of women neither of whom have breast cancer at the beginning of the study; one of the groups would possess the possible risk factor and the other group would not. The number of new cases of breast cancer in the two groups would be compared over time.

From: 4, Understanding Breast Cancer Risk

Cover of Saving Women's Lives
Saving Women's Lives: Strategies for Improving Breast Cancer Detection and Diagnosis.
Institute of Medicine (US) and National Research Council (US) Committee on New Approaches to Early Detection and Diagnosis of Breast Cancer; Joy JE, Penhoet EE, Petitti DB, editors.
Washington (DC): National Academies Press (US); 2005.
Copyright © 2005, National Academy of Sciences.

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