On February 3, 2016, CMS published a proposed rule that would revise the methodology CMS uses to measure the performance of accountable care organizations (ACOs) in the Medicare Shared Savings Program (Shared Savings Program) in order to encourage participation in the program.  In particular, the proposed rule would modify the methodology CMS uses to reset performance benchmarks for ACOs that continue participation in the Shared Savings Program after an initial three-year agreement period by incorporating regional expenditures, which would make the ACO’s cost target more independent of its historical expenditures and more reflective of fee-for-service spending in its region.  The proposed rule also would modify the methodology used for adjusting the ACO’s benchmark for composition changes and changes in the health status of the ACO’s assigned population.  In addition, CMS proposes an alternative participation option to encourage ACOs to enter performance-based risk arrangements earlier in their Shared Savings Program participation.  Finally, CMS would establish rules for reopening determinations of ACO shared savings and shared losses.  Comments on the rule will be accepted until March 28, 2016.