Everybody into the pool! Medicare in the twenty-first century.

Both the President and now Republicans have proposed to slow the growth of Medicare costs by allowing seniors to join private managed care health insurance plans. In this article, the author demonstrates that a private market in health insurance will not function like a "normal" commercial insurance market, will constantly be undermined by adverse selection, and therefore is unlikely to achieve the objectives for which it is being created. This result follows from established principles of commercial insurance and our modern understanding of the pathophysiology of disease.