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average FFS per capita costs for the payment year for each area are the basis for MA rates, as required by the statute. Published in conjunction with the CY 2026 Advance Notice are two files with 2023 ratebook experience. The first file reflects an approximation of experience using the legacy approach based on the “Denominator methodology.” The second file includes experience from the proposed approach, in which beneficiary statuses are pulled directly from the Common Medicare Environment (CME). Stakeholders can use these two published datasets to assess the geographic impact of the CME approach to the tabulation of 2023 non-ESRD ratebook experience. A description of the differences between the Denominator and CME approaches is on pages 30- 31 of the CY 2026 Advance Notice. The key differences in the Denominator and CME approaches are as follows: • There are two key changes in the determination of ratebook fee-for-service (FFS) enrollment: o The beneficiary county of residence in the Denominator system was determined annually as of March 1 of the following year. For example, the county of residence for CY 2022 experience was based on the beneficiary’s county of residence as of March 1, 2023. Under the proposed CME approach, the county of residence is determined monthly. The Enrollment Database is the source for the beneficiary county of residence for both the Denominator and CME approaches. o ESRD status in the Denominator was determined annually as of March 1 of the following year based on the beneficiary’s Medicare Status Code (MSC). Under the proposed CME approach, the beneficiary’s ESRD status is determined monthly from the transplant and dialysis tables. • The county of residence and ESRD status for Denominator claims is from claim records in the National Claims History (NCH) system. In the proposed CME approach, the beneficiary’s county of residence and ESRD status for claims is based on the applicable values in the CME for the month of service. • Enrollment and non-hospice claims for FFS beneficiaries in hospice status are included in the Denominator experience and excluded in the CME experience. Table II-4 on page 31 of the CY 2026 Advance Notice illustrates the dollar impact of the update to tabulate ratebook FFS experience beginning in 2023. The corresponding impact of the revision on the non-ESRD USPCC trend is -0.06% for 2024, -0.07% for 2025, and -0.04% for 2026. The enrollment for both the legacy and revised approach is derived from the same source, the Medicare Enrollment Database (EDB).