The application of epidemiological knowledge, reasoning, and methods to study clinical issues and improve clinical care. “Clinical” should not be restricted to “medical. “Medical epidemiology” is a complementary and commonly used term. Research often addresses etiological, mechanistic, diagnostic, therapeutic, and prognostic medical issues, is conducted in clinical settings, is led by clinicians, and has patients as study subjects. While clinical epidemiology uses epidemiological principles mostly to aid decision-making involving sick individuals, the wider Context is also commonly considered.^{6, 9, 26, 42, 58, 128, 201, 203, 224, 225} See also clinical decision analysis; n-of-one study.