The changing demand for health care.
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D003710:Demography; D006301:Health Services Needs and Demand / Q000639:trends*; D006302:Health Services Research / Q000639:trends*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008875:Middle Aged; D011153:Population; D014481:United States