From Lawton Burns and Mark Pauly in Health Affairs:
The evidence reviewed above suggests that components of accountable care organizations have limited and uncertain impact, especially on cost savings, and thus provide little support for the two postulates mentioned above: that better care coordination will improve quality at any given cost, and that the organizations will lower Medicare’s rate of spending growth. If the organizations increase “value” (quality or outcome divided by cost), at best they raise the numerator but do not lower the denominator. […]
We ought to have realistic expectations about our ability to deliver on the Triple Aim [of improving care for individuals and populations and controlling costs]. Prior to the publication of an article by Donald Berwick and coauthors in this journal, economists and others commonly referred to inevitable tradeoffs between cost, quality, and access—what was then labeled the “iron triangle.” There is still no firm evidence that anyone knows how to achieve the Triple Aim. Recent evidence illustrates one crucial point: Improving quality for some conditions often increases costs.
Much more in their paper.