Risk factor analysis and nomogram model construction for mortality in patients following colonic perforation surgery

Figure 2 Model performance. A: Receiver operating characteristic curve of the four-variable nomogram. The area under the curve (AUC) value was 0.852 (95% confidence interval: 0.791-0.913), indicating excellent discrimination for 30-day mortality; B: Calibration plot comparing predicted vs observed mortality probabilities. The dashed 45° line represents perfect calibration; the solid line represents the model-based fit. A Brier score = 0.072 and slope ≈ 1 indicate high agreement across the entire risk range, supporting direct clinical use without further probability recalibration; C: Decision curve analysis. Decision curve for the nomogram across clinically relevant threshold probabilities (1%-40%). The net benefit of the model exceeds that of the “treat-all” (orange dashed) and “treat-none” (green dashed) strategies over the entire range, confirming clinical utility; D: Threshold sensitivity plot. Sensitivity, specificity, accuracy and F1 score vs probability threshold. The vertical dotted lines mark the two selected cut-offs: 0.020 (high-sensitivity screen) and 0.121 (optimal Youden/F1 point), supporting the dual-threshold funnel strategy. ROC: Receiver operating characteristic.