Data: Medicare enrollment is based on analysis of the Centers for Medicare & Medicaid Services Chronic Conditions Data Warehouse 2020 research-identifiable Master Beneficiary Summary File (MBSF) Base. The estimates are based on a 20% sample of Medicare beneficiaries.

Sample Definition: Medicare beneficiaries were required to have both Part A and Part B in March 2020 to be included in this analysis. Dual-eligible individuals were identified based on their dual status in March 2020. This analysis includes people in the 50 States, Puerto Rico, and Washington, D.C. Individuals without a valid state and county code were excluded. This approach is consistent with other KFF analysis of Medicare Advantage enrollment in some ways, but differs from previous analyses of dual-eligible individuals in four main ways: first, in previous analyses individuals with Medicare Part A or Part B were included. Second, in previous analyses dual eligibility included individuals who were dually eligible for Medicare and Medicaid at any point during the year, whereas in this study dual eligibility was defined in the month of March. Third, previous analyses included only people living in the 50 states and the District of Columbia, in contrast this analysis includes people living in Puerto Rico as well. Finally, previous analyses did not require a valid county code to identify where individuals lived. As a result, this analysis includes a lower number of dual-eligible individuals (10.6 million) than KFF reports elsewhere (12.5 million).

Traditional Medicare enrollment: Beneficiaries without a valid Medicare Advantage contract ID in March 2020 were defined as enrolled in traditional Medicare. This analysis does not identify beneficiaries who are aligned to an Accountable Care Organization or who receive their Medicare benefits through a Financial Alignment Initiative managed FFS program. Additionally, this analysis is unable to identify traditional Medicare beneficiaries who have employer-sponsored or self-purchased supplemental insurance coverage because this information is not included in the MBSF data.

Medicare Advantage enrollment: This includes enrollment in all private plans including Medicare Advantage plans. Beneficiaries with a valid contract ID in March 2020 were identified as enrolled in Medicare Advantage. To determine the type of plan in which the beneficiary was enrolled, the contract ID and plan ID were matched to the March 2020 Monthly Enrollment by Plan or the Special Needs Plan Report data published by CMS.

Medicare Advantage plans include SNPs (D-SNPs, I-SNPs and C-SNPs), individual plans and employer plans and other types of private plans include: Program for All-Inclusive Care (PACE) plans, Medicare-Medicaid Plans, section 1876 cost contract plans, and section 1833 health care prepayment plans (HCPP plans). In this analysis non-Medicare Advantage plans are included in the Medicare Advantage enrollment totals, in contrast to other KFF analyses, which have excluded these types of plans. When those plans are excluded, the share of Medicare beneficiaries with both Part A and Part B that are in a Medicare Advantage plan is slightly lower.

Identifying Dual-Eligible Individuals: Dual eligibility was identified based on the dual-eligible status code in March 2020. Those who had a dual eligibility code of 02, 04, or 08 were assigned full-benefit dual eligibility status and those with a code of 01, 03, 05, or 06 were assigned partial-benefit dual eligibility status. In Puerto Rico, individuals were also flagged as dual-eligible individuals if they were enrolled in a coordination-only D-SNP in March 2020. All other Medicare beneficiaries were identified as Medicare beneficiaries without Medicaid.

Race/Ethnicity. Race/ethnicity was identified using the variable RTI race code in the MBSF which was developed by the Research Triangle Institute using an algorithm.

Geographical identifiers. A metropolitan statistical area consists of the county or counties (or equivalent entities) associated with at least one urbanized area of at least 50,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties. A micropolitan statistical area consists of, “the county or counties (or equivalent entities) associated with at least one urban cluster of at least 10,000 but less than 50,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties. Rural statistical areas are all other non-metropolitan and non-micropolitan areas.

Appendix Tables

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