Introduction to Epidemiology

Epidemiology concerns itself with the incidence, distribution, cause, control, and prevention of disease. In contrast to other branches of medical science that focus on the health status of individuals, epidemiology is the study of the health status of populations. Epidemiology employs the tools of basic science (e.g., observation, hypothesis testing, statistics, correlation, and causal reasoning) to protect, promote, and restore health and well-being in populations. This chapter discusses the fundamental principles of descriptive and analytic epidemiology. Our goal is not to provide definitive descriptions of all elements of population-based medical research, but rather to explain the rudiments of the science of epidemiology and create a context in which topics presented in subsequent chapters can be understood. We define the concepts of incidence and prevalence, outline the basic epidemiological principles of risk and association, discuss the various types of studies used to conduct epidemiological research, and caution against forces and factors that may threaten the validity and reliability of such studies. We also consider the theoretical and practical constraints on making claims of causation in epidemiology. We explore the differences between traditional, public health epidemiology and clinical epidemiology. Finally, we discuss the role of the concepts of sex, gender, race, and ethnicity in epidemiology, and we encourage health professionals to define and deploy these socially charged categories with care.