NORC and its subcontractor KPMG LLP obtained access to 100% Medicare FFS claims data through the Centers for Medicare and Medicaid Services (CMS) Virtual Research Data Center (VRDC). Medicare data included a number of analytic files containing FFS claims organized into files by type of care, such as carrier files (also known as the Physician/Supplier Part B claims files), outpatient files, as well as denominator files (with information on eligibility and enrollment). Through the VRDC, the project team had access to 100% CMS research identifiable files (RIFs), including:
- Skilled Nursing Facility.
- Home Health.
- Durable Medical Equipment (DME).
- Master Beneficiary Summary File (MBSF) Base File.
- MBSF Chronic Conditions segment file.
- Part D Event data.
- Part D Characteristics, including Drug, Pharmacy, Prescriber, and Plan characteristics.
Please see the Research Data Assistance Center websiteExternal for a CMS description of each file.
The VEHSS analysis of Medicare claims is subject to a number of potential limitations:
- Medicare claims are intended for billing purposes only. Diagnosis information included on claims is intended to justify payment. Therefore, diagnosis data on claims may suffer from bias or limited detail.
- Medicare FFS does not cover all healthcare services, such as routine eye exams or optometry care. Medicare patients may utilize these services using a different payer, and thus these services are not captured in Medicare FFS claims.
- Patients may be insured by multiple insurers, such as a supplemental, medigap or Medicare managed care plans. Thus, even normally covered ophthalmology services may not be indicated in FFS claims if services were reimbursed by another plan.
- Many Medicare patients move seasonally. We report patient residence using the last location of observation. This may skew patient numbers towards “sun belt” states.
- Medicare is not nationally representative for individuals younger than 65 years. These patients may obtain Medicare coverage due to medical need, such as legally recognized disability, or other specially defined benefit, such as end-stage renal disease. Individuals who become disabled for reasons of blindness cannot be distinguished from others who are disabled unless their visual condition of low vision and blindness is recording in their medical claims.
- Medicare FFS is nearly representative of the population aged 65 and older, but does not include beneficiaries with Medicare advantage plans, people who defer Medicare coverage, or services paid out of pocket.
 US Census Bureau. Profile america facts for features: CB17-FF.08. Washington, DC: Economics and Statistics Administration; 2017. https://www.census.gov/content/dam/Census/newsroom/facts-for-features/2017/cb17-ff08.pdf. Accessed March 1, 2018.