In fact,epidemiology is often described as the basic science of public health, and for good reason. First, epidemiology is a quantitative discipline that relics on a working knowledge of probability, statistics, and sound research methods. Second, epidemiology is a method of causal reasoning based on developing and testing hypotheses grounded in such scientific fields as biology, behavioral sciences, physics, and ergonomics to explain health-related behaviors, states, and events. However, epidemiology is not just a research activity but an integral component of public health, providing the foundation for direction practical and appropriate public health action based on this science and causal reasoning.