Yuval Levin notes that CBO is admitting that their projections are intrinsically wrong:

What we have here, in other words, is a frank admission by CBO that their methodology ignores the effects of policy changes on the behavior of both providers and consumers—effects which must, of course, be essential to the consequences of any health-care reform.

This methodological “gap” strongly favors the left in the health-care debate, because it assumes that the economics of health care are just a matter of manipulating levels of spending, and so that crude price controls will not affect access and quality and that market competition will not reduce costs. There is, of course, ample evidence of the former effect (especially in Medicaid, which in most states pays doctors at even lower rates than Medicare, at least for now), and there is some evidence of the latter too (though market forces haven’t had much of a chance to be tried, except in the Medicare prescription-drug benefit; other experiments (like Medicare advantage) all take place in the shadow of the existing fee-for-service Medicare system and so can’t really change the behavior of providers—they therefore have neither traditional Medicare’s ability to boss doctors around nor a market system’s ability to keep costs down, so they end costing no less than traditional Medicare, and sometimes even a little more.)

It’s the same kind of scam that they pull when they statically score the effect of a change in tax rates. It’s lunacy to assume that it will have no effect on behavior, and yet they do, and so delude themselves that they can predict with any confidence the resulting revenue.