Book excerpt: Principles of Epidemiology: A Self-Teaching Guide consists of a series of problem-solving exercises designed to introduce and guide readers toward an understanding of the principles and methods of epidemiology, rather than the epidemiology of specific diseases or subject areas such as ""infectious disease"" or ""chronic disease"" epidemiology. The guide has been formulated to be used by itself or as a supplement to standard textbooks. It illustrates and illuminates the principles and concepts of epidemiology and provides the reader an opportunity to practice the application of these principles in a logical sequence. The guide is divided into 14 exercises. Each exercise will help readers to understand principles or methods used by epidemiologist. Topics covered include the patterns of disease, populations at risk and risk assessment, screening for disease, investigation of an epidemic, etiology of disease, principles of causation, study design in epidemiologic investigation, data interpretation, and the uses and applications of epidemiology.