Enhancement of Identifying Cancer Specialists through the Linkage of Medicare Claims to Additional Sources of Physician Specialty

An understanding of variations in the delivery and outcomes of clinical care by physician specialty can be used to target education and interventions to the most relevant professional societies and training programs. The assessment of these variations, however, depends on the quality of the data used to measure physician specialty. The Surveillance, Epidemiology, and End Results (SEER)-Medicare dataset, which consists of cancer registry data linked to Medicare enrollment and claims files, contains physician specialty on the claims and is commonly used by health services researchers to examine specialty-related variations in care of people with cancer (Earle et al. 2002, 2006; Keating et al. 2003; National Cancer Institute 2007). Information about physician specialty available on Medicare claims can be supplemented by linking to sources such as the Unique Physician Identification Number (UPIN) Registry or the American Medical Association (AMA) Physician Masterfile (AMA 2004; NHIC 2006). Baldwin et al. (2002) reviewed the availability and quality of data on physician characteristics in Medicare claims and found that while these data are useful, investigators must understand the limitations of data on physician specialty so that they might decide the best approach to a particular research question and how these limitations may affect findings. For example, Rosenblatt and colleagues found that the AMA Masterfile identified 97 hematologist/oncologists in Washington state in addition to the 58 hematologist/oncologists found in that state's Medicare claims, a 167 percent increase (Rosenblatt et al. 1998; Baldwin et al. 2002). Thus, researchers investigating the role of hematologist/oncologists potentially would underestimate the number of physicians with this specialty if using Medicare claims alone. The extent to which there is agreement on cancer-specific physician specialty variables between Medicare claims, the UPIN Registry, and the AMA Masterfile for the entire SEER-Medicare dataset is unknown. Given the additional time and financial investment that is required to obtain and link the UPIN Registry and/or the AMA Masterfile to SEER-Medicare data, we believe a more complete understanding of the agreement on cancer-specific physician specialty between these data sources would be useful. Such information could be used by future investigators to determine whether seeking additional data on specialty will enhance the quality of their cancer-related research. The purpose of this paper is to compare the agreement and identification of physicians by cancer specialty between SEER-Medicare claims, the UPIN Registry, and the AMA Masterfile. We also demonstrate an approach to refine the determination of physicians as cancer specialists when using all three data sources, and we provide an overview of Medicare claims-based information on physician specialty, including the process of obtaining the data.