Table 2.

Cutoff points in IGDS9-SF between diagnostic positive and negative groups (N = 131).

Cutoff	True positive	True negative	False positive	False negative	Sensitivity (100%)	Specificity (100%)	PPV (100%)	NPV (100%)	Accuracy (100%)	Youden's Index (100%)
21	57	37	37	0	100	50.0	60.6	100	71.7	50
29	57	58	15	0	100	78.4	78.0	100	87.7	78.4
30	57	65	8	0	100	87.8	86.3	100	93.1	87.8
31	57	69	7	0	100	89.2	87.6	100	93.8	89.2
32	57	74	5	0	98.0	91.9	91.9	100	96.1	90.1
33	52	74	0	5	86.0	95.9	100	93.6	96.1	81.9
34	46	74	0	11	77.2	97.3	100	87.0	91.6	74.5
35	41	74	0	16	70.2	98.6	100	82.2	87.1	68.8
36	39	74	0	18	68.0	100	100	80.4	86.2	68.0
A*	42	74	0	15	73.6	100	100	83.1	88.5	73.6

IGDS9-SF, Nine-Item Internet Gaming Disorder Scale–Short-Form; sensitivity, the proportion of true positive rates; specificity, the proportion of the true negative rates; PPR, positive predictive rate; NPR, negative predictive rate; Youden's Index, defined as sensitivity + specificity − 1; AUC = 0.998.

A*: indicated the cutoff point of five or more of the nine IGD criteria on the basis of answering “very often.”