Fig. 5

Calibration plots of the nomogram in the training cohort (a), validation cohort (b) and external cohort (c). The x-axis represents the nomogram’s predicted probability, and the y-axis represents the actual probability of POPIs. The long-dotted line represents the ideal curve, the short-dotted line represents the apparent curve, and solid black line represents the bias-correction curve by bootstrapping (B = 1000 repetitions). The calibration plots revealed good predictive accuracy between the actual probability and predicted probability in the three cohorts