It is difficult to generalize about MCOs because they take many different forms.
Although most medical care practitioners are familiar with the notions of
whether MCOs are open panel or closed panel, an HMO or a PPO, these
descriptions do not convey the variability of MCO organization. This variability
makes it very difficult for physicians or the public to know with certainty what
the MCO provides and how to best deal with it. The variability also causes
legal problems for MCOs and their medical care practitioners because
administrative practices that might be legal under one organizational structure
are illegal in others. For example, the rules governing physician incentives
under Medicare prohibit practices that are legal for private pay patients.
[Medicare and Medicaid Programs, Requirements for Physician Incentive Plans
in Prepaid Health Care Organizations, 61 Fed. Reg. 69,034 (Dec. 31, 1996).]