SEER-Medicare: How the SEER & Medicare Data are Linked

The linkage of the SEER-Medicare data is a collaborative effort of the NCI, the SEER registries, and the Centers for Medicare & Medicaid Services (CMS). NCI and CMS perform the linkage of persons in SEER to their Medicare claims. Investigators seeking to use the data are not involved in or responsible for the linkage.

To link SEER with Medicare data, the registries participating in the SEER program send individual identifiers for all persons in their files. These identifiers are matched with identifiers contained in Medicare's master enrollment file. The linkage was first completed in 1991 and has subsequently been updated, most recently, every two years. For each linkage update, approximately 95 percent of persons age 65 and older in the SEER files were matched to the Medicare enrollment file. NCI and CMS plan to continue updating the SEER-Medicare linkage every two years.

Beginning with the 2020 data release, persons appearing in the SEER data were linked with Medicare records if the listed Social Security Number (SSN) and date of birth (at least month and year) matched or, when the SSN was incomplete or missing, if the listed last name, sex, and full date of birth matched.