• Lori A Pollack, Walter Adamache, Christie R Eheman, A Blythe Ryerson, and Lisa C Richardson.
• Epidemiology and Applied Research Branch, Division of Cancer Prevention and Control, Centers for Disease Control and Prevention, Atlanta, GA 30341-3717, USA. lpollack@cdc.gov
• Health Serv Res. 2009 Apr 1;44(2 Pt 1):562-76.

ObjectiveTo examine the number of cancer specialists identified in three national datasets, the effect of combining these datasets, and the use of refinement rules to classify physicians as cancer specialists.Data Sources1992-2003 linked Surveillance, Epidemiology, and End Results (SEER)-Medicare data and a cancer-free comparison population of Medicare beneficiaries, Unique Physician Identification Number (UPIN) Registry, and the American Medical Association (AMA) Masterfile.Study DesignWe compared differences in counts of cancer specialists identified in Medicare claims only with the number obtained by combining data sources and after using rules to refine specialty identification.Data ExtractionWe analyzed physician specialty variables provided on Medicare claims, along with the specialties obtained by linkage of unencrypted UPINs on Medicare claims to the UPIN Registry, the AMA Masterfile, and all sources combined.Principle FindingsMedicare claims identified the fewest number of cancer specialists (n=11,721) compared with 19,753 who were identified when we combined all three datasets. The percentage increase identified by combining datasets varied by subspecialty (187 percent for surgical oncologists to 50 percent for radiation oncologists). Rules created to refine identification most affected the count of radiation oncologists.ConclusionsResearchers should consider taking the additional effort and cost to refine classification by using additional data sources based on their study objectives.

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