Fig. 3

a Internal validation of the nomogram model yielded a C-index value of 0.780 (95% CI, 0.747–0.813), which was identical to the area under curve of the receiver operating characteristic curves. b The internal calibration curve showed optimal agreement between nomogram predictions and actual observations. c Data for the validation group were used for the external validation of the nomogram model, which yielded a C-index value of 0.739 (95% CI, 0.684–0.794)