Our Master Beneficiary Summary File (MBSF) - Base Segment (A/B/C/D) files have the following data about individuals enrolled in Medicare between 1999 and 2021:
For 1991 - 1998 data, refer to the Denominator (DN) Files.
The table below lists variable categories for and some key variables in MBSF - Base Segment data. For a comprehensive list of variables, review the MBSF - Base Segment data dictionary.
Age, Beneficiary Identification Number, Date of Birth, Date of Death, Gender, Race, Residence County Code, Residence State, Residence Zip Code
Eligibility & Enrollment
Dual Eligibility Status, Monthly Enrollment Counts (A/B/C/D), Part C Plan and Enrollment Information, Part D Low-Income Cost Sharing, Part D Plan and Enrollment Information, Reasons for Entitlement, State Buy-In Indicators
1999 - 2021
File Update Frequency
COVID Studies: Monthly
Non-COVID Studies: Quarterly or Annual
Data Dictionary LinkVisit the Data Documentation Page
NIA Data Partners Offering MBSF - Base
CE, HRS, LLFS, NSHAP, PT, PSAD, PSID, RADC, UFOVT, WLS
NIA Data Partners Not Offering MBSF - Base
BLSA, HABC, NHAS, NHATS, NLTCS, UAS