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Using G-Computation to Estimate the Effect of Regionalization of Surgical Services on the Absolute Reduction in the Occurrence of Adverse Patient Outcomes

Austin, Peter C., PhD*,†,‡; Urbach, David R., MD, MSc*,†,§,∥

doi: 10.1097/MLR.0b013e31829a4fb4
Original Articles

Background: Numerous studies have found that increased hospital or surgeon operative volumes, as measured by the number of procedures performed, are associated with improved patient outcomes after surgery. These findings have been used to support important health policy decisions about regionalization of surgical services, in which provision of specific surgical services is restricted to hospitals that maintain operative volumes above a specified threshold. The most common statistical approach in volume-outcome studies is to regress patient outcomes on a set of patient characteristics and a variable denoting provider volume. When outcomes are binary, such as operative mortality, logistic regression is used, resulting in the odds ratio being the reported measure of association. However, the odds ratio is a relative measure of effect and does not allow policy makers to estimate the absolute benefit of regionalization.

Objectives: To describe how G-computation can be used to estimate the expected number of lives saved due to regionalization of surgical services.

Research Design: Retrospective cohort design of patients undergoing 1 of 3 different surgical procedures in Ontario, Canada.

Results: Regionalization of colorectal cancer surgery, esophagectomy, or pancreaticoduodenectomy in Ontario could reduce the average annual number of perioperative deaths by 20.2, 2.0, and 3.6, for the 3 procedures, respectively.

Conclusions: The absolute reduction in number of operative deaths due to regionalization of surgical procedures can be calculated. This can help inform health policy debate about benefits of regionalization.

*Institute for Clinical Evaluative Sciences

Institute of Health Management, Policy and Evaluation

Dalla Lana School of Public Health, University of Toronto

§University Health Network

Department of Surgery, University of Toronto, Toronto, ON, Canada

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Supported by the Institute for Clinical Evaluative Sciences (ICES), which is funded by an annual grant from the Ontario Ministry of Health and Long-Term Care (MOHLTC). The opinions, results and conclusions reported in this paper are those of the authors and are independent from the funding sources. No endorsement by ICES or the Ontario MOHLTC is intended or should be inferred. P.C.A. is supported in part by a Career Investigator award from the Heart and Stroke Foundation. This study was supported in part by an operating grant from the Canadian Institutes of Health Research (CIHR) (Funding number: MOP 86508).

The authors declare no conflict of interest.

Reprints: Peter C. Austin, PhD, Institute for Clinical Evaluative Sciences, G1 06, 2075 Bayview Avenue, Toronto, ON, Canada M4N 3M5. E-mail:

© 2013 by Lippincott Williams & Wilkins.