For most managed care plans, beneficiaries elect to participate in the plan. In exchange, beneficaries often have lower premiums, but often restricted access to providers (e.g., referral requirements, copayment differentials for out-of-network physicians).

Medicare’s Accountable Care Organizations (known as Shared Savings Plans (SSP)) also assign beneficaries to organizations. The SSPs are groups of providers that are responsible for a set of beneficiaries and can earn bonuses if they are able to save Medicare money and improve quality. Unlike managed care plans, however, beneficaries do not choose to participate in an ACO; Medicare assigns beneficiaries to ACOs based on where they receive care. Unlike managed care plans, beneficaries do not have any in/out-of-network limitations or referral restrictions, even though ACOs are responsible for their care. Thus, it is crucial that the assignment of beneficiaries to SSPs is reliable.

A study by McWilliams et al. (2013), however, states that reliable attribution my be compromised in the current system. They write:

For the purpose of assignment, both the SSP and Pioneer program define primary care as specific sets of evaluation and management (E&M) services delivered not only in outpatient settings but also in skilled nursing facilities (SNFs) and nursing homes This definition ensures that long-term nursing home residents no longer receiving primary care in the community are still eligible for assignment to ACOs that include nursing homes…

including nursing home E&M services in the assignment process appropriately allows for ACO contracts to apply to long-term nursing home residents if such partnerships should develop…

For community-dwelling beneficiaries, however, counting E&M services provided in SNFs as primary care services could transfer the locus of accountability from primary to post-acute care providers as an unintended consequence. Specifically among beneficiaries who receive both outpatient primary care and short-term post-acute care, the assignment rules may selectively assign the sickest patients requiring the most post-acute care away from community primary care providers, and thus away from ACOs that do not include SNFs in their contracting networks.

Will the inclusion of post-acute E&M services into the attribution method affect the SSP to which beneficiaries are assigned in practice? The authors find that the answer is yes.

Assignment shifts occurred for 27.6 percent of 25,992 community-dwelling beneficiaries with at least one post-acute skilled nursing facility stay, and they were more common for those incurring higher Medicare spending. Those whose assignment shifted constituted only 1.3 percent of all community-dwelling beneficiaries cared for by large ACO-eligible organizations (n = 535,138), but they accounted for 8.4 percent of total Medicare spending for this population.

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