The effect of patient selection on comorbidity-adjusted operative mortality risk: Implications for outcomes studies of surgical procedures

Urbach, David R.; Bell, Chaim M.

« Previous Next »Journal of Clinical Epidemiology
Volume 55, Issue 4 , Pages 381-385, April 2002

The effect of patient selection on comorbidity-adjusted operative mortality risk:

Implications for outcomes studies of surgical procedures

David R. Urbach
- Department of Surgery, University of Toronto, Toronto, Ontario, Canada
- Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada
- Clinical Epidemiology and Health Care Research Program, University of Toronto, Toronto, Ontario, Canada
- Division of Clinical Decision Making and Health Care, Toronto General Hospital Research Institute, Toronto, Ontario, Canada
- Corresponding author. Toronto Western Hospital, 399 Bathurst Street, Room MP8-332, Toronto, Ontario, Canada M5T 2S8, Tel: 416–603–5426; fax: 416–603–5436. E-mail address:(D.R. Urbach)
Chaim M. Bell
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Institute of Medical Science Program in Clinical Epidemiology and Health Services Research, University of Toronto, Toronto, Ontario, Canada

Received 14 July 2000; received in revised form 23 October 2001; accepted 4 November 2001.

Abstract

Consumers of outcomes research may assume that risk-adjustment procedures based on patients' comorbid conditions will control for baseline prognostic differences between comparison groups, so that differences in risk-adjusted outcomes represent effects other than those due to differences in comorbidity severity. However, surgeons may differ in their threshold to operate on patients with different intensities of the same comorbidity, which may not be accounted for using commonly employed risk-adjustment methods. We developed a model to explore the effect that selection based on comorbidity severity could have on estimates of the risk-adjusted relative risk (RR) of operative death. Larger effects on the apparent RR of operative death were observed when both the proportion of patients in the high-risk (“selected”) stratum and the relative increase in the risk of death due to being in the high-risk stratum were large. Biased estimates of the risk-adjusted RR of operative death will be observed if surgeons differentially select patients based on comorbidity severity and if differences in comorbidity severity are not captured by the risk-adjustment methodology.

Keywords: Selection bias, Risk adjustment, Comorbidity adjustment, Operative mortality rate, Surgical procedures