At the end of 2018, the Centers for Medicare and Medicaid Services published the Pathways to Success final rule for the Medicare Shared Savings Program (MSSP) giving accountable care organizations (ACOs) renewing July 1, 2019, or later the option to select between prospective and retrospective assignment of patients.
Under prospective assignment, beneficiaries are assigned to an ACO based on services occurring prior to the performance year. Under retrospective assignment, beneficiaries are assigned to an ACO based on services occurring during the performance year. Averages for assignment-eligible fee-for-service beneficiaries can help provide understanding of how the two assignment methodologies affect results.
Retrospective and prospective assignment have significantly different effects on the characteristics of the assigned populations for beneficiaries assigned to primary care physicians and specialists. Prospective and retrospective assignment will ultimately affect the population that is assigned to the ACO because some beneficiaries who are assigned under prospective assignment are not assigned under retrospective and vice versa. The choice between these assignment methodologies can have subtle effects on the ACO’s overall benchmark, risk score, and performance year costs.
In this brief, Milliman’s Sam Shellabarger, Charlie Mills, and Lance Anderson explore in more detail the potential effects of prospective and retrospective assignment on key ACO metrics under the MSSP.