Patterns of medical care among users of hospital emergency units.
D003710:Demography; D004636:Emergency Service, Hospital / Q000706:statistics & numerical data*; D010044:Outpatient Clinics, Hospital / Q000706:statistics & numerical data*; D010414:Pennsylvania; D010820:Physicians / Q000706:statistics & numerical data*; D012111:Residence Characteristics; D012959:Socioeconomic Factors