> My understanding is that doctors can choose not to take Medicare patients. Sort of. For example, most emergency rooms in which physicians have admitting priv

> My understanding is that doctors can choose not to take Medicare patients. Sort of. For example, most emergency rooms in which physicians have admitting privileges to an associated hospital are required to take Medicare[0]. And those emergency rooms are prohibited from refusing patients based on insurance status. So right off the bat, that's an enormous source of patients who could be publicly insured (Medicare/Medicaid) or uninsured, and they have no legal way to refuse them. (Once a patient is in the ER, if they need to be admitted, you can't (legally!) refuse to admit them based on their insurance status). I'm kind of oversimplifying, because there are a lot of tricks that hospitals try to use to stop the bleeding - for example, Bellevue is a public hospital, and it operates an emergency room, but its private counterpart that is literally across the street does not. NYU can do some (perfectly legal) maneuvering to keep most of the patient population of Langone limited to privately-insured patients. As a result, Langone has undeniably better[1] care, despite having access to the same set of medical staff[2] and being associated with the same medical college. It's true that private practices can refuse Medicare for outpatient services easily. And incidentally, many do. There's a reason that, except in "critical access" areas[3], most of the top physicians who operate purely private practices don't accept Medicare. However, private practices are a dying breed, so that's a moot point in 2017. [0] Conversely, free-standing emergency rooms are prohibited from accepting Medicare. A rather cynical view of this would be that Medicare does not want to encourage free-standing emergency rooms, because it's much more difficult to use private emergency care to subsidize Medicare care than it is to use private inpatient care to subsidize Medicare care (the orders of magnitude in costs are vastly different). [1] More expensive, but vastly better [2] Well, sort of. Staff isn't shared between the hospitals day-to-day (a nurse at Langone will typically only work at Langone unless he or she also has a job at Bellevue), but the allocation draws from the same pool a priori. [3] Rural hospitals that Medicare pays handsomely, because otherwise those regions would have no medical access at all.