Health: a state of complete physical, mental and social well-being. Epidemiology: study of the distribution of disease within a population. Incorporates several disciplines (public health, medicine, biology and sociology) Epidemiologist: a scientist who studies the social origins and distribution of health problems in a population and how patterns of illness and disease vary between and within societies. Morbidity: the amount of disease, impairment, and accidents in a population. Acute condition is short term (no more than 3 months) and a chronic condition is a long-term health problem. Morbidity may be measured according to the incidence and prevalence of speci c illnesses and disease. Incidence: the number of new cases of a speci c health problem within a given population during a speci ed period. Prevalence: the total number of cases of a condition within a population that exists at a given time. More groups are at a higher risk for infection and death.