NATIONAL BUREAU OF ECONOMIC RESEARCH
NATIONAL BUREAU OF ECONOMIC RESEARCH

Measuring Physician Practice Competition Using Medicare Data

Laurence Baker, Kate Bundorf, Anne Royalty


This chapter is a preliminary draft unless otherwise noted. It may not have been subjected to the formal review process of the NBER. This page will be updated as the chapter is revised.

Chapter in forthcoming NBER book Measuring and Modeling Health Care Costs, Ana Aizcorbe, Colin Baker, Ernst Berndt, and David Cutler, editors
Conference held October 18-19, 2013
Forthcoming from University of Chicago Press
in NBER Book Series Studies in Income and Wealth

Questions about the market structure of physician practices have become prominent in contemporary health policy discussions. Market forces recently appear to favor the growth of larger multi-specialty groups. Larger practices could lead to improvements in health care quality and outcomes by improving coordination, but they may be more difficult to effectively manage and, if inefficient, could drive higher costs of care. Larger practices may also increase concentration in health care markets. While concentration has been well studied in the case of hospitals, there is less evidence about impacts of structural changes in physician markets. A primary reason is a lack of regularly collected, broadly based data on practice market structure. In this paper, we explore the creation of physician practice concentration measures using Medicare claims data. Medicare claims are available for large numbers of patients over time and can be used to identify important characteristics of physician practices. We use claims data to construct measures of practice size and Hirschman-Herfindahl Indices (HHIs) for physician practices between 1998 and 2010, and explore variations in measures of size and concentration. We also discuss a number of issues that arise in the construction of claims-based measures that may affect their validity and interpretation.

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