The importance of intervening early in the course of the disease or even before the disease develops is well-known and considered ideal by many physicians. The benefits of incorporating prevention into medical practice have become apparent with the decline in incidence of diseases like poliomyelitis and rubella as a result of childhood immunization, with stroke reduction attributed to earlier detection and treatment of hypertension, and with reduction of morbidity and mortality from coronary heart disease due to control of modifiable risk factors.