Figure S1 Trends in the descriptive properties of assessment questionnaires throughout the years. The descriptive properties of assessment questionnaires followed non-linear Gaussian curves throughout the years. (A) Number of items: reduced χ2 = 2.44, adjusted r2 = 0.32, two-tailed Fisher statistic F(4,10) = 919.01, P < 0.0001. (B) Number of factors (inversed): reduced χ2 = 0.54, adjusted r2 = 0.33, two-tailed Fisher statistic F(4,10) = 171.20, P < 0.0001. (C) Number of items per factor: reduced χ2 = 0.69, adjusted r2 = 0.55, two-tailed Fisher statistic F(4,10) = 216.48, P < 0.0001

Table S1 Instruments excluded from the sample and corresponding exclusion criteria. More than 360 papers were identified, the vast majority of which were ignored for not having a questionnaire name or acronym appearing in the title and/or the abstract. Of the 30 questionnaires remaining after the first selection, 16 instruments were excluded according to exclusion criteria presented above. The final sample was composed of 14 questionnaires. Specifically, questionnaires which used DSM criteria for substance abuse or pathological gambling, but substituted ‘substance abuse’ with ‘internet abuse’ and ‘gambling’ with ‘internet’, were excluded. Questionnaires assessing disorders (e.g. pathological gambling) not perpetrated on the internet were also excluded. Questionnaires assessing video-gaming were not excluded from the sample because video-gaming is conceptually very close to internet addiction and are generally defined similarly as ‘technological addictions’.

Table S2 Additional attributes of the selected questionnaires. This Table presents the instruments' validation populations, descriptive properties, model fit to the data and sampling adequacy. Additional measures of the construct validity of the questionnaires, including the item factor loadings, the variance explained by the model and the factor eigenvalues, are included. Correlations are shown in italics.

Table S3 Dimensional structure of the questionnaires. All 67 individual factors of the questionnaires pooled into the seven dimensions of addiction according to their conceptual similarity. The questionnaires included here are: the Chinese Internet Addiction Inventory (CIAI), the Compulsive Internet Use Scale (CIUS), the Game Addiction Scale (GAS), the Generalized Problematic Internet Use Scale (GPIUS), the Generalized Problematic Internet Use Scale 2 (GPIUS2), the Internet Addiction Test (IAT), the Internet Consequences Scales (ICONS), the Internet Related Problem Scale (IRPS), the Online Cognition Scale (OCS), the Problematic Internet Use Questionnaire (PIUQ), the Problematic Internet Usage Scale (PIUS), the Problem Video Game Playing Test (PVGT), the Revised Internet Addiction Test (R-IAT) and the Revised Online Cognition Scale (R-OCS).

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