Hierarchical patterns in the location of physician specialists among counties.
D002321:Career Choice; D002755:Choice Behavior; D004470:Economics, Medical; D006301:Health Services Needs and Demand; D006280:Health Workforce; D006608:Hierarchy, Social; D006801:Humans; D008511:Medicine; D010820:Physicians / Q000600:supply & distribution*; D012930:Social Dominance; D012959:Socioeconomic Factors; D013038:Specialization; D014481:United States