In the final rule, CMS chose to adopt a preliminary prospective assignment methodology with final retrospective reconciliation.  Under this model, CMS will create a list of beneficiaries likely to receive care from the ACO based on primary care utilization during the most recent periods for which adequate dates are available, and provide a copy of the list to the ACO.  During the performance year, CMS will update the list periodically on a rolling basis to allow the ACO to adjust to likely changes in its assigned population.  At the end of each performance year, CMS will reconcile the list to reflect beneficiaries who actually meet the criteria for assignment to the ACO during the performance year.  Determination of shares savings or losses for the ACO will be based on this final, reconciled population.

CMS chose this approach because it believes that it will provide the ACO with adequate information to redesign care processes while also encouraging ACOs to standardize care for all Medicare FFS beneficiaries instead of a subset.  At the same time, CMS believes that the model will provide adequate incentives for each ACO to provide quality care to its beneficiary population.

CMS has also announced a Pioneer ACO Model which will test alternative savings and alignment.  The Pioneer ACO Model will provide CMS with the opportunity to gain experience and evaluate a more prospective hybrid model than the approach explained above.  CMS will study the Pioneer ACO Model and will consider its experiences in the next rulemaking.

Majority vs. Plurality Rule for Beneficiary Assignment

The Act requires that beneficiaries be assigned to “an ACO based on their utilization of primary care services” furnished by an ACO professional who is a physician, but it does not prescribe the methodology for such assignment.  For its methodology, CMS adopted a plurality of primary care services model, defined in terms of allowed charges, as follows:

CMS considered whether to assign beneficiaries to an ACO when they receive a plurality of their primary care services from an ACO, or to adopt a stricter standard under which a beneficiary will be assigned to an ACO only when he or she receives a majority of their primary care services from an ACO.  CMS chose a plurality methodology because it would result in a greater number of beneficiaries being assigned to an ACO, thus promoting statistical stability and a greater incentive for ACOs to redesign care processes.  Additionally, CMS voiced that the plurality methodology promotes ACO accountability for patients that might otherwise fall through the cracks because they would not meet a majority standard.

  • No Plurality Threshold:  CMS declined to set a threshold requirement on the plurality of primary care services methodology.  This will maximize the number of patients assigned to an ACO.
  • Simple Service Count vs. Accumulated Allowed Charges:  CMS could determine the plurality of services on the basis of a simple service count for each visit or on the basis of the accumulated allowed charges for services delivered.  The method of using a plurality of allowed charges would place greater weight on more complex primary care services in the assignment methodology, while a simple service method count would weigh all primary care encounters equally in determining assignment.  CMS chose to adopt the accumulated allowed charges method count, which put responsibility on the ACO providing the highest complexity and intensity of primary care services.  Additionally, this method results in the assignment of responsibility for containing costs to the provider who generates the most costs.