The Center analyzed Medicare claims data obtained from the Centers for Medicare and Medicaid Services (CMS). For the digital mammography analysis, the Center used a subset of the data submitted by physicians, hospitals and clinics from 2003 to 2008, the last year available at the time the data were acquired. Denied claims were excluded.
For privacy purposes and other reasons, the Center was limited to a 5 percent sample of national Medicare Part B data that contain claims for medical procedures, such as mammography, and used mainly by researchers and consultants. Besides limitations of sampling, the data have only the quarter in which a procedure was performed, not actual dates. And a permanent federal injunction prevents naming individual doctors who received payment for the claims.
Results from the 5 percent sample were multiplied by 20 to give a national scope to analyzed trends, an accepted survey research technique. However, even with a sample this large, it is impossible to account for all types of errors in the data. This means all calculations are estimates and rounded and must be considered imprecise.
The analysis of Medicare claims for mammography, liquid-based cytology and prostate-specific antigen tests was based on procedure codes obtained from documents and guidelines put out by CMS and the U.S. Preventive Services Task Force, a panel of medical experts. Some codes were also confirmed by professionals in the field.
The Center relied on the number of claims billed to indicate trends and frequency for the corresponding test. However, a claim cannot be equated with a procedure. Certain procedures (including mammograms) can be billed in multiple claims. In order to protect patients’ identities, some information, such as the date of a claim, was removed from the data, making it impossible to isolate procedures.
The overall price for each test included the payments Medicare made to physicians, hospitals and clinics. According to CMS’s Research Data Assistance Center (ResDAC), some claims (about 7 percent of the claims analyzed) incorrectly include a small amount of interest on the first line of payment. Therefore the payment amounts, like all else in the data, cannot be considered exact.
For the total mammography cost, the Center included the amount of money Medicare paid for computer-aided detection (CAD), an optional add-on that highlights for radiologists areas on a screening image that may contain tumors.
When calculating the additional cost of digital mammography over six years, the Center projected the total cost of mammography each year as if film were the only option, assuming that the number of mammograms would stay the same and that the average cost would remain constant within any given year.