Weiner M, Stump TE, Callahan CM, Lewis JN, McDonald CJ. A practical method of linking data from Medicare claims and
a comprehensive electronic medical records system. Int J Med Inf. 2003 Aug;71(1):57-69.
BACKGROUND: Linking administrative and clinical databases provides opportunities for richer studies to improve healthcare,
but linkage may require sophisticated algorithms. Linking US Medicare data with large databases used for everyday clinical
practice is seldom described in detail in medical literature.
OBJECTIVES: Test a deterministic method of linking data from a local electronic medical records system to Medicare data, and
report specific details of the algorithm used as well as lessons learned from the linkage process.
SUBJECTS: Medicare beneficiaries with medical encounters in selected Indiana counties in the 5-year period ending in 1999.
RESULTS: For 6388 beneficiaries with Medicare data indicating inpatient encounters in the system, 98% had links to the
clinical database. Of 7231 patients hospitalized and registered in the local clinical system, 86% contained a link to
Medicare data, and 69% contained a link even without using Social security number (SSN) as an identifier. Medicare data
that conflicted with local hospital records by indicating no local hospitalization occurred in 1.8%. More than 2000 claims
contained hospital identifiers that did not exist in the hospital codebook.
CONCLUSIONS: Details of a practical, deterministic method of linking Medicare claims to a large electronic records system
have been applied and described. Most records were linked without SSN. A variety of inconsistencies were found and these,
along with missing or incomplete data, can influence linking. Integrity of specific variables must be assessed carefully.
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