Prevalence of AD in populations is dependent upon different factors including incidence and survival. Two main measures are used in epidemiological studies&colon; incidence and prevalence. Both the global incidence of disease and resulting mortality have declined in recent years. Zinc deficiency contributes to an increased incidence and severity of diarrhea. A supplementation is advantageous in reducing disease incidence. There is a decreased incidence of stroke. It is associated with a decrease in the incidence of bronchopulmonary dysplasia. Prolonged fever is associated with a higher incidence of cardiac involvement. Efficacy and adverse reaction incidence are similar to Dryvax. The reason for the decreased incidence in the elderly is unclear. Government campaigns decreased the incidence of infanticide. Hormonal mechanisms could explain the increased incidence of SLE in females. It also created local atmospheric conditions that contributed to an increased incidence of malaria. Screens for gastric cancer using photofluorography due to the high incidence there. Uranium miners have a higher incidence of cancer.