Epidemiology is defined as the study of the distribution and determinants of health-related states or events in populations, and the application of this study to control health problems. The aims of epidemiology include describing disease occurrence, assessing disease importance, explaining disease etiology, predicting disease, evaluating prevention and control, and controlling disease distribution. Common epidemiological study designs include cohort studies, case-control studies, cross-sectional studies, and occupational studies. Key epidemiological concepts include incidence, prevalence, sensitivity, specificity, and confounding factors.