Supplementary Material for: Development and Validation of a Short-Form Internet Overuse Screening Questionnaire for Adults

<b><i>Aims:</i></b> The aim of the current study was to develop and validate a short-form of the internet overuse screening questionnaire (IOS-Qs). <b><i>Methods:</i></b> A total of 571 adults were recruited from a representative, stratified, and multistage cluster sample. Among participants, 188 and 383 were used in the development and validation of the IOS-Qs, respectively. <b><i>Results:</i></b> Experts’ ratings and Rasch model analyses led to the selection of 8 items from the IOS-Qs; latent-class analysis using these 8 items revealed an estimated prevalence of 8.6% (33 out of 383) of problematic internet over-users. Problematic internet over-users were positively associated with a 1-year prevalence rate of any mental disorder (OR 3.08, <i>p</i> = 0.008), mood disorder (OR 7.11, <i>p</i> = 0.003), and depressive disorder (OR 5.22, <i>p</i> = 0.016). The receiver operating characteristic curves identified an optimal cutoff score of 9.5 for differentiating problematic internet over-users from unproblematic internet users with 94% sensitivity and 94% specificity. <b><i>Conclusion:</i></b> The results suggest that the IOS-Qs was valid, and items including social isolation were crucial to the brief distinction of at-risk internet users. Because of its brevity, the questionnaire can be effectively administered as a large-scale survey.