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The Impact of Surgeon Specialization on Patient Mortality: Examination of a Continuous Herfindahl-Hirschman Index

Hall, Bruce Lee MD, PhD, MBA*†‡§; Hsiao, Esther Y. BA§; Majercik, Sarah MD, MBA; Hirbe, Mitzi RHIA, CPHQ§; Hamilton, Barton H. PhD

doi: 10.1097/SLA.0b013e3181a335f8

Objective: To examine the effect of surgeon specialization on patient outcomes, controlling for volume.

Background: There is great interest in the degree to which surgical specialization affects outcomes, particularly considering drives to measure and reward quality in healthcare. Although surgical specialization has been previously analyzed with respect to outcomes, most studies have treated it as a dichotomous variable based on academic credentials. We treat it here as a continuous variable defined quantitatively by procedural diversity.

Methods: We used 2002 to 2005 patient data from the National Surgical Quality Improvement Program for the Department of Surgery, Barnes Jewish Hospital, St. Louis, Missouri. To quantitate procedural specialization, Herfindahl-Hirschman indices for surgeons were calculated using billing codes. These indices were calculated according to 3 different levels of procedural aggregation. Using conditional logit models, we examined the relationship between these indices and 30-day postoperative mortality rates.

Results: Surgeon specialization was inversely related to mortality rates after adjusting for case volume when indices were calculated using medium procedural aggregation (odds ratio for mortality = 0.580 per 0.1 unit Herfindahl increase; P = 0.025) or low aggregation (odds ratio for mortality = 0.510 per 0.1 unit Herfindahl increase; P = 0.015). No relationship was observed at the high level of aggregation.

Conclusions: The procedural concentration component of surgical specialization is correlated with improved mortality rates independently of case volume. However, how broadly or narrowly “specialization” is defined has an impact on this relationship.

Surgeon specialization was assessed using a continuous Herfindahl-Hirschman index based on billing codes, and at low and medium levels of aggregation this measure demonstrated correlation between increased specialization and improved 30-day mortality rates using National Surgical Quality Improvement Program data. However, the specification of “specialization” remains relevant.

From the *Department of Surgery, John Cochran Veterans Affairs Medical Center, St Louis, Missouri; †Washington University Center for Health Policy, St Louis, Missouri; ‡Division of Endocrine and Oncologic Surgery, Department of Surgery, Olin Business School at Washington University in St Louis, St Louis, Missouri; §Department of Surgery, Washington University School of Medicine, St Louis, Missouri; and ¶Department of Surgery, Alpert Medical School of Brown University, Providence, Rhode Island.

Supported in part by the Center for Health Policy, under the direction of Dr. William Peck, Washington University in St. Louis, St. Louis, MO.

Reprints: Bruce Lee Hall, MD, PhD, MBA, Campus Box 8109, 660 South Euclid Ave, Saint Louis, MO 63110-1093. E-mail:

© 2009 Lippincott Williams & Wilkins, Inc.