The impacts of supplemental benefits on Medicare Advantage plan composition.

In 2019 and 2020, Medicare Advantage (MA) plans received historic flexibility to begin to address members' nonmedical and social needs through a set of primarily health-related benefits (PHRBs) and Special Supplemental Benefits for the Chronically Ill (SSBCIs). We aimed to evaluate the impact of adoption on the number and composition of new MA plan enrollees. A difference-in-differences design of retrospective Medicare enrollment data linked to publicly available plan and county-level data. We linked individual-level Medicare enrollment data to publicly available, plan-level MA benefit, crosswalk, and penetration files from 2016 to 2020. We compared the number of new enrollees and the proportion of new enrollees who were Black, Hispanic, younger than 65 years, partially and fully Medicare and Medicaid dual eligible, and disabled in plans that adopted a PHRB or SSBCI vs a set of matched control plans that did not. In fully adjusted models, PHRB adoption was associated with a 2.2% decrease in the proportion of fully dual-eligible new members (95% CI, -4.0% to -0.5%). SSBCI adoption was associated with a 2.3% decrease in the proportion of new members younger than 65 years (95% CI, -3.6% to -0.9%). After accounting for multiple comparisons, these results were no longer statistically significant. We determined that supplemental benefit adoption was not associated with demographic shifts in MA plan enrollment.