The marketplace doesn't determine how many doctors the nation has, as it does for engineers, pilots and other professions. The number of doctors is a political decision, heavily influenced by doctors themselves.

And Congress also controls the supply of physicians by how much federal funding it provides for medical residencies — the graduate training required of all doctors.

To become a physician, students spend four years in medical school. Graduates then spend three to seven years training as residents, usually treating patients under supervision at a hospital. Residents work long hours for $35,000 to $50,000 a year. Even doctors trained in other countries must serve medical residencies in the USA to practice here.

Medicare, which provides health care to the nation's seniors, also is the primary federal agency that controls the supply of doctors. It reimburses hospitals for the cost of training medical residents.

The United States stopped opening medical schools in the 1980s because of the predicted surplus of doctors. The Association of American Medical College