SEER-Medicare: Medicare Enrollment Data

The Centers for Medicare & Medicaid Services (CMS) maintains an annual Master Beneficiary Summary File (MBSF) that includes all Medicare beneficiaries. This file has multiple segments, as briefly described below. A more detailed explanation can be obtained hereExternal Web Site Policy from the Centers for Medicare and Medicaid’s (CMS’s) Chronic Conditions Data Warehouse (CCW).

  1. Base (A/B/C/D)External Web Site Policy contains information on the person’s date of birth, date of death (if any), sex, race, state of residence, and monthly enrollment in Part A (inpatient), Part B (outpatient), Part C (Medicare Advantage/ managed care/ HMO) and Part D (prescription drug coverage).
  2. Chronic Conditions Flags DocumentationExternal Web Site Policy contains first occurrence date, mid-year flag, and end year flag to indicate the presence or absence of 27 conditions, based on Medicare services provided beginning in 1999. As a proxy of evidence for the presence of a condition, these flags are determined based on the presence of treatment for the conditions using claims-based algorithms that were created by CMS and are available on the Chronic Conditions WarehouseExternal Web Site Policy website. Because the flags are determined using claims data it is not possible to ascertain the information for beneficiaries enrolled in managed care/HMOs. This limitation also applies to newly-eligible Medicare beneficiaries who may have only a partial year of FFS coverage. Thus, in order for the flag to indicate the presence of a condition, the claims for the beneficiary must indicate treatment for that condition and the beneficiary must also have had continuous Part A/B-FFS coverage during the specified time period. It is important to note that the major objective for creating the flags was to allow for a quick, initial identification and extraction of beneficiaries with a given condition from the larger Medicare population. The flag definitions were intended to be broad, so that researchers could extract the data based on the flag definitions and then refine their specifications as needed for their specific analyses. The condition definitions were not intended to calculate population statistics.
  3. Other Chronic or Potentially Disabling Conditions documentationExternal Web Site Policy contains first ever occurrence date and end year occurrence date for an additional 35 chronic or potentially disabling conditions not included in the above chronic conditions segment (e.g., mental health; tobacco, alcohol and drug use; developmental disorders; disability related conditions; behavioral health conditions); claims-based algorithms are available on the Chronic Conditions WarehouseExternal Web Site Policy website. Again, these flags are determined based on Medicare services provided beginning in 1999; therefore, the same considerations outlined above pertaining to the chronic condition flags should be taken with these flags.
  4. Plan Characteristics FileExternal Web Site Policy contains Medicare Advantage plan and Prescription Drug Plan information separated into six subfiles: base/benefit file, premium file, cost sharing tier file, service area file, special needs plans file and multi-year crosswalk file. The information in the Plan Characteristics File can be linked to the Part D Drug Event File (using contract ID and plan ID) to assess for variation in utilization and costs by plan type. Please note, plan identifiers in the data were encrypted prior to 2015; the multi-year crosswalk file allows tracking plans across time. For more information (e.g., file layout and codebooks) please visit the Chronic Conditions WarehouseExternal Web Site Policy; documentation for file years 2007-2014 is listed under the Medicare Part D heading and file years 2015+ under the Medicare Enrollment heading.

Given there are two cohorts of persons included in the SEER-Medicare data (persons with and without cancer), there are two subsets of MBSF data available via SEER-Medicare (MBSF-Cancer and MBSF-Control); the file documentation is the same. The MBSF-Control can be used to identify controls for the persons with cancer or to develop population-based estimates of health care utilization, e.g. use of cancer tests such as PSA and mammography in the entire population. The persons in the MBSF-Control file have been identified from a random 5% sample of Medicare beneficiaries residing in the SEER areas. If a person in the 5% sample is diagnosed with cancer they are removed from the MBSF-Control file and will only appear in the MBSF-Cancer file. Like all persons with cancer reported to a SEER registry, their cancer information will be included in the SEER-Medicare Cancer File with a flag to indicate that they are in the 5% sample. Additionally, these persons will be included in the SEER-Medicare 5% Cancer File, which is a subset of the SEER-Medicare Cancer File (e.g., restricted to cancer diagnoses only among persons included in the 5% sample).

Last Updated: 21 May, 2021