In recent years epidemiology has become an increasingly important approach in both public health and clinical practice. Epidemiology is the basic science of disease prevention and plays major roles in developing and evaluating public policy relating to health and to social and legal issues. Together with laboratory research, epidemiology is now used to identify environmental and genetic risk factors for disease and to shed light on the mechanisms involved in the pathogenesis of different diseases. The heightened media attention that epidemiology has recently received has major implications for health care providers and policy makers as well as for epidemiologists. As a result of this scrutiny, the approaches, methodology, and uses of epidemiology have garnered increasing interest from an everbroadening group of professionals in different disciplines as well as from the public at large. This book is an introduction to epidemiology and to the epidemiologic approach to problems of health and disease. The basic principles and methods of epidemiology are presented together with many examples of the applications of epidemiology to public health and clinical practice. The ifth edition of this book retains the general organization and structure of the previous editions. In this edition, a list of learning objectives has been added at the beginning of most chapters to help direct the reader’s attention to the major issues to be found in that chapter, and a number of new review questions have been added at the end of certain chapters. The ifth edition consists of three sections. Section 1 focuses on the epidemiologic approach to understanding disease and to developing the basis for interventions designed to modify and improve its natural history. Chapter 1 provides a broad context and perspective for the discipline, and Chapter 2 discusses how disease is transmitted and acquired. Chapters 3 and 4 present the measures we use to assess the frequency and importance of disease and demonstrate how these measures are used in disease surveillance— one of the major roles of epidemiology in public health. Chapter 3 discusses measures of morbidity, and Chapter 4, measures of mortality. Chapter 5 addresses the critical issue of how to distinguish people who have a disease from those who do not, and how to assess the quality of the diagnostic and screening tests used for this purpose. Once people who have a certain disease have been identiied, how do we characterize the natural history of their disease in quantitative terms? Will they die from their disease or develop some other serious outcome? Or will their disease be successfully managed? Such characterization is essential if we are to identify any changes in survival and severity that take place over time, or changes that result from preventive or therapeutic interventions (Chapter 6). Because our ultimate objective is to improve human health by modifying the natural history of disease, the next step is to select an appropriate and effective intervention—a selection that ideally is made using the results of randomized trials of prevention and of treatment (Chapters 7 and 8).

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