In the Medicare Shared Savings Program (MSSP), accountable care organizations (ACOs) have financial incentives to lower spending and improve quality. In this article they used quasi-experimental methods to assess the early performance of MSSP and ACOs. In the conclusions they found that the first full year of contracts MSSP was associated with reductions in Medicare Early pass between the 2012 participants but not among the 2013 participants. Economies higher in primary care groups independent groups in integrated hospitals. 

Source:

The New England Journal of Medicine