To explore whether the IRT item-level estimates suggested similar information as sensitivity/specificity analyses (Table 4), ROC-AUC was calculated (Fig. 3). ROC-AUC considers sensitivity and specificity together; a value of 1.0 (100%) indicates that the item accurately classifies cases of a SUD defined by the DSM-IV Checklist. Consistent with IRT results, items that shifted to the severe ends on ICCs (Fig. 2a–2e) showed low ROC-AUC values (≤0.70): withdrawal for alcohol, cannabis, cocaine, and sedatives; time using for alcohol and sedatives; and giving up activities for sedatives (Fig. 3). Taking larger amounts (high discrimination, low-to-medium severity on ICCs) demonstrated good-to-excellent levels of classification (ROC-AUC >0.80), especially for alcohol (ROC-AUC =0.91) and cannabis (ROC-AUC=0.90); tolerance (high discrimination, medium severity on ICCs) showed an excellent classification (ROC-AUC=0.93) for sedatives.
