Risk adjustment for health plans disproportionately enrolling frail Medicare beneficiaries

There is concern about the adequacy of diagnosis-based risk adjusters for paying health plans that disproportionately enroll frail Medicare beneficiaries. The Medicare Current Beneficiary Survey (MCBS) was used to examine the ability of two risk-adjustment models to predict Medicare costs for groups defined by institutional status and difficulty with activities of daily living (ADLs). Both models underpredicted average costs for non-institutionalized frail beneficiaries; however, the models slightly overpredicted expenses for most frail individuals and severely underpredicted for a minority. Further refinements are needed if diagnosis-based models are used to pay plans that disproportionately enroll frail beneficiaries.