Nomogram Performance in Risk Stratification

The survival of each patient in the study was estimated based on a total nomogram score. X-tile plots were constructed to divide the training cohort into four groups based on nomogram scores. The most effective cutoff points were determined following correction for the use of minimum P statistics by Miller-Siegmund P-value correction.²³ After the best cutoff values for the training groups were selected, they were applied to the validation cohorts. The cohorts were divided into low, low-intermediate, high-intermediate, and high-risk subgroups based on total nomogram scores of the patients. ROC and Kaplan–Meier survival curves were used to compare the discriminative ability of the nomogram in predicting survival with that of the Ann Arbor Stage.

The net reclassification index (NRI) and integrated discrimination improvement (IDI) of the nomogram were also calculated and used to evaluate the degree of improvement in the sensitivity and specificity of the nomogram compared with those of the Ann Arbor Stage system. NRI was used to assess differences in the number of PINHL patients correctly classified by the nomogram and the Ann Arbor Stage at a given cut-off point, thereby comparing the predictive power of the two models.²⁴ IDI reflects differences in the prediction probability gap between the two models, which is based on prediction probability for each individual patient in the disease model. The criteria for IDI are the same as those for NRI.