Predictive accuracy study: Comparing a statistical model to clinicians' estimates of outcomes after coronary bypass surgery

Background. The purpose of this study was to compare clinicians' prior prob ability estimates of operative mortality (OM) and prolonged intensive care unit stay (ICU) length of stay greater than 48 hours after coronary artery bypass graft surgery (CABG) with estimates derived from statistical models alone. Methods. Nine clinicians estimated the predicted probability of OM and ICU stay greater than 48 hours from an abstract of information for each of 100 patients selected from the 1996 to 1997 database of 1,904 patients who unde rwent isolated CABG. Logistic regression models were used to calculate the predicted probability of OM and ICU stay greater than 48 hours for each pat ient. The study sample was split into two parts; clinicians were randomly g iven access to a predictive rule to guide their judgements for one part of the study. Results. Clinicians' estimates were similar with or without access to the r ule, and both parts of the study were therefore pooled. Clinicians signific antly overestimated the probability of OM (model 6.3% +/- 1%, clinicians 7. 6% +/- 3%, p = 0.0001) and ICU stay greater than 48 hours (model 25% +/- 2% , clinicians 28% +/- 1%, p = 0.0012). Clinicians' estimates of OM were not significantly higher than the model's for nonsurvivors (0.8% +/- 0.7%, p = 0.2), but were significantly higher for survivors (1.4% +/- 0.3%, p = 0.039 ). Conclusions. Clinicians trusted their own empiric estimates rather than a p redictive rule and overestimated the probability of OM and ICU stay greater than 48 hours. (Ann Thorac Surg 2000;70:162-8) (C) 2000 by The Society of Thoracic Surgeons.