Predictors of Mortality
Multivariable analysis (Table 4) identified the following variables as independent predictors of mortality: 1) age (Odds Ratio [OR] = 1.05, per 5-year increment), the need for urgent/emergent surgery (OR = 5.46) and left ventricular ejection fraction (LVEF) < 40% (OR = 2.14). Surgical procedure (repair vs. replacement) was not an independent predictor of mortality. The 30-day mortality predictors were internally validated using a 1000-resampling bootstrap procedure that showed the stability of the results (Table 5 ). Moreover, there were no features of multicollinearity, as the standard errors of the affected coefficients were relatively small (Table 5 ). The c-statistic for this multivariable model was 0.80, with asymptotic 95% confidence of 0.75-0.86, indicating good discrimination of the model (Table 6 and Figure 1). The Hosmer-Lemeshow 2 statistic showed that the model goodness of fit was good (x2 = 2.78, p = 0.95), indicating good predictive performance (discrimination and calibration) of the derived model.