Columbia subject headings:
Ambulatory medical care--Utilization--United States--Statistics--Periodicals.
Emergency medical services--United States--Periodicals.
Medical care surveys--United States--Periodicals.
Harvard subject headings:
Ambulatory medical care--Utilization--United States--Statistics--Periodicals.
Emergency medical services--United States--Periodicals.
Medical care surveys--United States--Periodicals.
Princeton subject headings: