Screening and Diagnosis
Screening and diagnostic tests can detect diseases at early stages to promote potentially beneficial treatments. The interpretation of screening and diagnostic test results depends on the disease process of interest, the qualities of the test, and the context of testing. Screening tests seek to identify diseases before they have caused recognizable signs or symptoms. Diagnostic tests seek to verify the presence of diseases for which signs and symptoms are already apparent. The predictive values of any test are determined by the test validity (sensitivity and specificity) and the pretest probability of the disease. Observational studies that compare outcomes of people who undergo screening versus those who do not undergo such procedures require careful interpretation to ensure that bias has not occurred.