Epidemiology is the study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems. The term study includes both surveillance, whose purpose is to monitor aspects of disease occurrence and spread that are pertinent to effective control, and epidemiologic research, whose goal is to harvest valid and precise information about the causes, preventions, and treatments for disease. The term disease refers to a broad array of health-related states and events including diseases, injuries, disabilities, and death.