Epidemiology can be defined as the study of how diseases are spread in the public and the factors that affect or control this spreading. It can also be defined as a key facet of public health practice. The area aims to provide the intrusion of disorders and to popularize the health of human beings. The basic regions of trained medical specialty accept medical specialty analysis of public health records, health incidents of state and trend survey, public health police work and health code impact analysis. Or in other words it is the study of the distribution and determinants of the health related states or events in specified populations and the application of this study to control of health problems. Epidemiology and public health are often interrelated and stated as basic of each other, and for good reason. First, epidemiology is a calculative discipline that depends on a working knowledge of likelihood, count and sound research areas. Also epidemiology is a method of fresh reasoning based on developing and testing theory based in such scientific areas as biology, behavioral sciences, physics, and user-friendly to discuss health-related behaviors, states, and events. However, epidemiology is not only a research activity but an essential part of public health, providing the origin for directing practical and suitable public health action build on this science and innovative reasoning. Epidemiology is data-driven and depends on a structured and impartial approach to the collection, investigation and exposition of data. Basic epidemiologic methods gravitate to depend on cautious observation and use of rational comparison groups to evaluate whether what was perceived, such as the number of cases of disease in a certain region during a specific time period vary from what might be expected. However, epidemiology also focuses on techniques from other scientific fields, including biostatistics and informatics, with biologic, economic, social, and behavioral sciences.