Fig. 5

Calibration plot showing predicted (x-axis) versus observed (y-axis) probability of mortality. The bisector (red line) stands for the perfect agreement between observed and expected probability; at 95% confidence level, the calibration belt (grey color shaded region) encompass the bisector over the whole range of the predicted probabilities (the belt wasn’t observed under or over the red line). This suggests that the predicted probabilities estimated by the nomogram didn’t significantly deviate from the observed probability (that is, the model’s calibration is acceptable). Hence, at 95% confidence level, the calibration belt was neither under nor over the bisector (never under and over the bisector)