Epidemiology is the study of the distribution and determinants of disease frequency. In the fifth century BC, Hippocrates suggested that the development of human disease might be related to the external and internal environment of an
individual1. In the 1600s and 1800s in England, John Graunt and William Farr quantified vital statistics on the basis of birth and death records. In the 1850s, John Snow associated cholera with water contamination in London by observing higher cholera rates in homes supplied by certain water sources.