Epidemiology refers to the patterns of occurrence of a disease or its incidence in a given society or population. Epidemiology here represents the rates of either substance use, or abuse. The United States is the leader among all other countries for its development of a sophisticated method of monitoring substance abuse in its population. The clinician, lawmaker, or individual who wishes to be informed about substance abuse has a variety of tools to assess the degree of substance abuse occurring at any given time.