Mapping Physician Networks with Self‐Reported and Administrative Data

Relationships between health care providers are essential to a functioning health care system. Physicians rely on their relationships with physician colleagues for patient referrals (Gonzalez and Rizzo 1991), clinical advice (Keating, Zaslavsky, and Ayanian 1998), and information about the latest clinical advances (Gabbay and le May 2004). Given their importance, understanding the nature of such relationships could yield valuable knowledge about the emergence of local practice patterns and the diffusion of health care practices. This understanding could in turn inform health policy decisions aimed at modifying physicians' behavior. Since every doctor has a range of interactions with an array of other doctors, physicians are embedded within a network of relationships, or ties, with their physician colleagues. Using tools from the emerging field of complex network analysis (Newman 2003), physician professional networks defined by such formal or informal relationships can be analyzed at a deeper level than previously possible. Some studies have already begun using these methods to analyze health care networks, addressing topics such as the exchange of clinical advice, the diffusion of pharmaceutical use, or organizational performance and cost-efficiency (Keating et al. 2007; Christakis and Fowler 2010; Iyengar, Van den Bulte, and Valente 2010). A major hurdle to studying physician networks is the lack of data on physician relationships which limits the scope of many studies. For instance, Keating and colleagues studied information seeking among primary care physicians (PCPs) about issues related to women's health, but they studied only 38 doctors whom they surveyed personally. Such de novo survey work requires laborious ascertainment of each relationship among pairs of doctors to map a relationship network, which is a formidable barrier to replication across multiple hospitals or practices. One potential way to identify physician relationships would be to use records regarding patients shared between physicians, as identified in administrative databases. Furthermore, using shared patients to define relationships is clinically intuitive. Physicians often email, phone, or “curbside” a colleague with specific clinical questions or cases, and these informal requests for information are formalized when the patient is actually referred for care (Keating, Zaslavsky, and Ayanian 1998). Thus, the presence of shared patients in administrative data—arising because of referral, patient self-selection, administrative rules (e.g., insurer policies regarding second opinions), or even chance—may represent an important source of information about physician relationships that could be useful for large-scale studies using the tools of network science. In this study, we sought to validate the use of patient sharing identified in administrative data as a source of information on physician networks. To do so, we first identified physicians connected via shared patients in Medicare data. We then surveyed physicians in a large physicians' organization and asked them about their referral and information-sharing relationships with other physicians and evaluated the correspondence between those relationships and patient sharing measured by Medicare claims.