2.4.3. Discrimination and calibration

The predictive accuracy of the final model was assessed by discrimination evaluated by calculating the concordance index (Harrell’s C index)³⁴ and measured as the time-dependent incremental area under the receiver operating characteristic curve Heagerty’s integrated AUC (iAUC)³⁵ for the three models. Differences and 95% confidence intervals (CIs) between the outcome and model were calculated using a bootstrapping method. To identify improvements in the predictive capability by adding IHC markers in the base model (histological parameters only), the net reclassification improvement (NRI) and the integrated discrimination improvement (IDI)^36,37 at 3 and 5 years were computed. Calibration draw to the agreement between observed outcomes and predictive probabilities, and a bootstrap method was used to reduce bias.