Several classifications:
a)    Most important for law is the area of epidemiology – the study of the occurrence of disease in a population.  Addressed through statistics and is population based.
(1)    Incidence: the number of new cases in a given population in a particular period of time.  Incidence of anthrax is being calculated.
(2)    Prevalence: the number of cases which exist in a population at this present time.  Today, we might have 100,000 with head injuries.
(3)    Most legal activity looks at the impact of the environment on the individual.  EX: asbestos.  Look at the number of cancers caused by that environment and compare to the number of cancers that would occur if not in that environment.
b)    Clinical Study: looks at the accumulation of disease in individuals.  Can be descriptive (based on height, weight, etc) and sociological (how a culture is quantified scientifically)
c)    Clinical Trials: basis for understanding individual’s response to intervention in health care matters.  Find a new drug or find a cure for a particular disease.  Intervention includes surgical procedures, drugs, devices, etc.