Supplementary Data SUPPLEMENTARY FIG. S1. Forest plot of Cronbach s a for all samples (24 groups).

Supplementary Data SUPPLEMENTARY FIG. S1. Forest plot of Cronbach s a for all samples (24 groups).

Forest plot of Spearman s correlation for college/university with a single de- SUPPLEMENTARY FIG. S2. partment subgroup.

SUPPLEMENTARY FIG. S3. Funnel plot for college/university with a single department subgroup.

SUPPLEMENTARY FIG. S4. Funnel plot for middle-/high-school older than 15 years of age subgroup.

Supplementary Table S1. PRISMA Guideline Checklist Section/topic # Checklist item Reported on page # Title 1 Identify the report as a systematic review, meta-analysis, or both. 1 Structured summary 2 Provide a structured summary including the following sections, as 2 applicable: background; objectives; data sources; study eligibility criteria, participants, and interventions; study appraisal and synthesis methods; results; limitations; conclusions and implications of key findings; and systematic review registration number. Introduction Rationale 3 Describe the rationale for the review in the context of what is already 3 known. Objectives 4 Provide an explicit statement of questions being addressed with reference 3 to participants, interventions, comparisons, outcomes, and study design (PICOS). Methods Protocol and registration 5 Indicate if a review protocol exists, and if so, where it can be accessed (e.g., 3 Web address). If available, provide registration information including registration number. Eligibility criteria 6 Specify study characteristics (e.g., PICOS, length of follow-up) and report 3, 4 characteristics (e.g., years considered, language, and publication status) used as criteria for eligibility, giving rationale. Information sources 7 Describe all information sources (e.g., databases with dates of coverage, 3 contact with study authors to identify additional studies) in the search and list the date last searched. Search 8 Present full electronic search strategy for at least one database, including 3 any limits used, such that it could be repeated. Study selection 9 State the process for selecting studies (i.e., screening, eligibility, included 3, 4 in systematic review, and, if applicable, included in the meta-analysis). Data collection process 10 Describe method of data extraction from reports (e.g., piloted forms, 4 independently, in duplicate), and any processes for obtaining and confirming data from investigators. Data items 11 List and define all variables for which data were sought (e.g., PICOS, 4, 5 Risk of bias in individual studies funding sources), and any assumptions and simplifications made. 12 Describe methods used for assessing risk of bias of individual studies (including specification of whether this was done at the study or outcome level), and how this information is to be used in any data synthesis. Summary measures 13 State the principal summary measures (e.g., risk ratio, difference in means). 4, 5 Synthesis of results 14 Describe the methods of handling data and combining results of studies, if performed, including measures of (e.g., I 2 ) for each metaanalysis. 4, 5 Risk of bias across studies Additional analyses Results Study selection Study characteristics Risk of bias within studies Results of individual studies 15 Specify any assessment of risk of bias that may affect the cumulative evidence (e.g., publication bias, selective reporting within studies). 16 Describe methods of additional analyses (e.g., sensitivity or subgroup analyses, meta-regression), if performed, indicating which were prespecified. 17 Give numbers of studies screened, assessed for eligibility, and included in the review, with reasons for exclusions at each stage, ideally with a flow diagram. 18 For each study, present characteristics for which data were extracted (e.g., study size, PICOS, follow-up period) and provide the appropriate citations. 19 Present data on risk of bias of each study and, if available, any outcomelevel assessment (see Item 12). 20 For all outcomes considered (benefit or harm), present for each study: (a) simple summary data for each intervention group, and (b) effect estimates and confidence intervals, ideally with a forest plot. 5 5, 6 5 6 6 6 6 8 (continued)

Supplementary Table S1. (Continued) Section/topic # Checklist item Synthesis of results Risk of bias across studies Additional analysis Discussion Summary of evidence Limitations Conclusions Funding Funding 21 Present results of each meta-analysis performed, including confidence intervals and measures of. 22 Present results of any assessment of risk of bias across studies (see Item 15). 23 Give results of additional analyses, if performed (e.g., sensitivity or subgroup analyses, meta-regression [see Item 16]). 24 Summarize the main findings including the strength of evidence for each main outcome; consider their relevance to key groups (e.g., healthcare providers, users, and policy makers). 25 Discuss limitations at the study and outcome levels (e.g., risk of bias) and at the review level (e.g., incomplete retrieval of identified research, reporting bias). 26 Provide a general interpretation of the results in the context of other evidence and implications for future research. 27 Describe sources of funding for the systematic review and other support (e.g., supply of data); role of funders for the systematic review. Reported on page # 6 8 8 6 8 8 8,9 9,10 10 PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Supplementary Table S2. Protocol Title Protocol for a systematic review of and of Internet Addiction Test (IAT) Date 01.27.2018 (This protocol had been made before we started to conduct a systematic review) 05.25.2018 Revised (Selection and exclusion criteria, Data analysis) Review question (PICOS) Systematic reviews on studies that verified the and of IAT, and showed outcome as psychometric properties for no limitation of participants or setting Searches (a) Search database: MEDLINE, Embase, PsycINFO, and CINAHL (b) Search filters: published after 2011 (c) Search queries: Internet-addiction-test, Internet-addiction-score, Internet-addiction-scale, or Young-test, Young-scale, Young-scale and various combinations of Medical Subject Headings (MeSH) terms relevant to query and psychometry that are known to optimize sensitivity (Agency for Healthcare Research and Quality guideline). Selection and exclusion criteria (a) Selection criteria: (a) Internet Addiction Test (IAT), original version; (b) articles that test or of the IAT (b) Exclusion criteria: (a) articles that compared the of the IAT with a distinct tool that measures adherence to medication, (b) articles that put priority on measuring Internet addiction among certain patient group than finding IAT s psychometric properties. Data extraction (selection and coding) (a) Identification of the study (author, title, and citation), country (language) (b) Characteristics of the study (objectives, design, and sample size, findings) (c) Psychometric properties of the instruments assessable: convergent,, criterion, internal, test retest, and so on Risk of bias (quality) assessment: Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) Patient selection, index, test, reference standard, flow and timing domain (a) Related to internal : risk of bias Section 1: Could the selection of patients have introduced bias? Section 2: Could the conduct or interpretation of the index test have introduced bias? Section 3: Could the reference standard, its conduct, or its interpretation have introduced bias? Section 4: Could the patient flow have introduced bias? (b) Related to external : applicability Section 1: Are there concerns that the included patients do not match the review question? Section 2: Are there concerns that the index test, its conduct, or its interpretation differ from the review question? Section 3: Are there concerns that the target condition as defined by the reference standard does not match the review question? Data analysis Cronbach s a was considered acceptable if between 0.7 and 0.9. For convergent, correlations of the IAT scores with comparator measures were considered moderate if >0.6 and high if >0.8. For, numbers of factors, selecting the number of samples by a guideline, method of extracting factors, method of choosing a number of factors, and a method of rotation were analyzed according to factor analysis guidelines. For the indices (Cronbach s a and Spearman s correlation coefficient, etc.) and the criterion indices (sensitivity, specificity), authors performed meta-analysis. Authors used a qualitative method to gather other types of evidence, such as known group, convergent, and.

Supplementary Table S3. Search Strategy Database: MEDLINE, CINAHL (01.01.2011-01.28.2018, month.date.year, published date) #1 (Internet-addiction-test) OR (Internet-addiction-scale) OR (Internet-addiction-score) OR (Internetaddiction-tests) OR (Internet-addiction-scales) OR (Internet-addiction-scores) 391 #2 (Young-test) OR (Young-scale) OR (Young s-test) OR (Young s-scale) OR (Young-tests) OR (Youngscales) OR (Youngs-tests) OR (Young s-scales) 10 #3 #1 OR #2 404 #4 (sensitiv* OR specific* OR (MH Research Measurement+ ) OR diagnos* OR (MH Diagnosis+ ) 4,463,482 #5 (reliab* OR valid* OR accura* OR psychomet* OR (MM Psychometrics OR reproduc* OR ( MH 1,121,908 Reproducibility of Results )) #6 (-coefficient OR Cronbach* OR internal- OR inter-rater OR test-retest OR interclass-correlation OR convergent OR criterion OR concurrent OR item-to-total OR factor-analysis) 162,469 #7 #4 OR #5 OR #6 4,915,100 #8 #3 AND #7 258 Database: Embase (01.01.2011-01.28.2018, month.date.year, published date) #1 Internet addiction test OR Internet addiction scale OR Internet addiction score OR Internet 459 addiction tests OR Internet addiction scales OR Internet addiction scores #2 Young test OR Young scale OR Youngs test OR Youngs scale OR Young tests OR 19 Young scales OR Youngs tests OR Youngs scales #3 #1 OR #2 478 #4 (sensitiv$ OR sensitive$ OR specific$ OR specificity$ OR sensitivity and specificity /exp OR diagnos$ 3,388,183 OR diagnosis /exp OR differential diagnosis /mj) #5 (reliab$ OR reliable$ OR $ OR /exp OR valid$ OR $ OR /exp 462,355 OR accura$ OR diagnostic accuracy /exp OR psychomet$ OR psychometry /exp OR reproduc$ OR reproducibility /exp) #6 ( coefficient OR Cronbach$ OR internal- OR inter-rater OR test retest 166,082 OR inter-class-correlation OR convergent OR criterion OR concurrent OR item to total OR factor analysis ) #7 #4 OR #5 OR #6 3,667,682 #8 #3 AND #7 192 Database: PsycINFO (01.01.2011-01.28.2018, month.date.year, published date) #1 (Internet-addiction-test) OR (Internet-addiction-scale) OR (Internet-addiction-score) OR (Internetaddiction-tests) OR (Internet-addiction-scales) OR (Internet-addiction-scores) 714 #2 (Young-test) OR (Young-scale) OR (Young s-test) OR (Young s-scale) OR (Young-tests) OR (Youngscales) OR (Youngs-tests) OR (Young s-scales) 12 #3 #1 OR #2 725 #4 (sensitiv* OR specific* OR diagnos* OR SU.EXACT.EXPLODE( Diagnosis ) OR 385,056 MJSUB.EXACT( Differential Diagnosis )) #5 (reliab* OR SU.EXACT.EXPLODE( Interrater Reliability ) OR SU.EXACT.EXPLODE( Test 176,058 Reliability ) OR SU.EXACT.EXPLODE( Statistical Reliability ) OR valid* OR SU.EXACT.EXPLODE( Statistical Validity ) OR SU.EXACT.EXPLODE( Test Validity ) OR accura* OR psychomet* OR SU.EXACT.EXPLODE( Psychometrics )OR reproduc*) #6 (-coefficient OR Cronbach* OR internal- OR inter-rater OR test-retest OR interclass-correlation OR convergent OR criterion OR concurrent OR item-to-total OR factor-analysis) 91,617 #7 #4 OR #5 OR #6 527,481 #8 #3 AND #7 379 CINAHL, The Cumulative Index to Nursing and Allied Health Literature.

Supplementary Table S4. Characteristics of Included Studies Country (language) Education level Sample size Age, mean years (range, SD) Sex (female, percent) Reference standard (definition of addiction group) Measurement of index test (Internet Addiction Test) Measurement of reference Reliability indices Waqas et al. S1 Pakistan (English) College (medical and dental only) 522 20 (17 25) 62.8 Asked each subject to complete Servidio S2 Italy (Italian) University 659 23.6 (3.8) 64.5 Asked each subject to complete Boysan et al. S3 Turkey (Turkish) Kaya et al. S4 Turkey (Turkish) Mohammadsalehi Iran (Persian) College et al. S5 (medical sciences only) College 453 21.9 (2.0) 63.5 Asked each subject to complete herself in the classroom University 407 20.1 (1.5) 65.8 Asked each subject to complete herself in the classroom, test retest, test retest 254 Unknown setting, test retest Hawi et al. S6 Poland (Polish) College 1,245 22.0 (6.0) 30.5 Online survey Guan et al. S7 Malaysia (Malaysian) Fioravanti and Casale et al. S24 Fernández-Villa College (medical only) Italy (Italian) High-school and university 162 19 66.1 Young s Diagnostic Questionnaire Face-to-face interview at the clinic by unknown interviewer 840 18.7 (3.9) 59.0 Asked each subject to complete herself in the classroom Face-to-face interview at the clinic by researchers trained by the psychiatrist Internal et al. S8, Spain (Spanish) College 851 Online survey test retest Dhir et al. S9 India (English) High-school 1,914 14.9 (1.5) 38.7 Asked each subject to complete Ahmad et al. S10 Jordan (Arabic) University 587 20.5 (2.6) 57.2 Asked each subject to complete Tsimtsiou Greece (Greek) College et al. S11 (medical only) 151 21.1 (3.5) 46.4 Asked each subject to complete herself in the classroom, test retest Validity indices criterion, (continued)

Supplementary Table S4. (Continued) Country (language) Education level Sample size Age, mean years (range, SD) Sex (female, percent) Reference standard (definition of addiction group) Measurement of index test (Internet Addiction Test) Measurement of reference Reliability indices Sung et al. S12 South Korea (Korean) Pontes et al. S13 Portugal (Portuguese) Karim and Bangladesh Nigar S14 (Bangla) Watters et al. S15 Canada (English) Lee et al. S16 South Korea (Korean) Middle-school High-school and university 1,722 13 15 51.8 Asked each subject to complete 593 19.0 (3.6) 69.0 Asked each subject to complete and online survey University 172 22.3 (2.0) 43.6 Asked each subject to complete High-school Lai et al. S17 China (Chinese) Middle- and highschool Hawi S18 Lebanon (Arabic) 1,948 17.1 (0.8) 59.0 Asked each subject to complete herself under the supervision of teachers and/or members of the research team University 279 19.9 (2.7) 62.8 Asked each subject to complete Middle- and highschool 844 15.9 (3.5) 62.3 Asked each subject to complete, test retest 817 15.0 (2.1) 59.5 Unknown setting Faraci et al. S19 Italy (Italian) College 485 24.1 (7.3) 67.7 Unknown setting Puerta-Cortés Spain (Spanish) General population et al. S20 (Internet users) Jelenchick United States et al. S25 of America (English) Conti et al. S21 Portugal (Portuguese) Barke et al. S22 Germany (German) Widyanto United Kingdom et al. S23 (English) 1,117 20.9 (4.8) 61.8 Online survey University 215 18.8 54.0 Online survey University 77 23.0 (3.7) 70.0 Asked each subject to complete College (psychology only) General population (Internet users) 1,041 (online) 841 (offline) 24.2 (7.2) 53.3 Online survey, test retest 23.5 (3.0) 53.2 Asked each subject to complete 225 28.0 (12.6) 69.0 Online survey SD, standard deviation. Validity indices

Supplementary Table S5. Quality Assessment of Diagnostic Accuracy Studies-2 Assessment of All Studies Risk of bias (internal ) Applicability (external ) Domain Patient selection Index test Reference standard Flow and timing Patient selection Index test Reference standard Waqas et al. S1 Low Unclear Low High Low Servidio S2 Low Low Low Low Low Boysan et al. S3 Low Low Low Low Low Kaya et al. S4 Low Low Low Low Low Mohammadsalehi et al. S5 Low Low Low High Low Hawi et al. S6 High Low Low Low Low Guan et al. S7 Low Unclear Unclear High High Low Unclear Fioravanti and Casale et al. S24 Low Unclear Low Low Low Fernández-Villa et al. S8 Low Low Low Low Low Dhir et al. S9 Low Unclear Low Low Low Ahmad et al. S10 Low Low Low Low Low Tsimtsiou et al. S11 Low Low Low High Low Sung et al. S12 Low Low Low Low Low Pontes et al. S13 High Low Low Low Low Karim and Nigar S14 Low Low Low Low Low Watters et al. S15 Low Low Low Low Low Lee et al. S16 Low Low Low Low Low Lai et al. S17 Low Low Low Low Low Hawi S18 Low Low Low Low Low Faraci et al. S19 Low Low Low Low Low Puerta-Cortés et al. S20 Low Low Low Low Low Jelenchick et al. S25 Low Low Low Low Low Conti et al. S21 Low Low Low Low Low Barke et al. S22 Low Low Low High Low Widyanto et al. S23 Low Low Low Low Low Supplementary References S1. Waqas A, Farooq F, Raza M, et al. Validation of the Internet Addiction Test in at a Pakistani medical and dental school. Psychiatric Quarterly 2017; 89:235 247. S2. Servidio R. Assessing the psychometric properties of the Internet Addiction Test: a study on a sample of Italian university. Computers in Human Behavior 2017; 68:17 29. S3. Boysan M, Kuss DJ, Barut Y, et al. Psychometric properties of the Turkish version of the Internet Addiction Test (IAT). Addictive Behaviors 2017; 64:247 252. S4. Kaya F, Delen E, Young KS. Psychometric properties of the Internet Addiction Test in Turkish. Journal of Behavioral Addictions 2016; 5:130 134. S5. Mohammadsalehi N, Mohammadbeigi A, Jadidi R, et al. Psychometric properties of the Persian language version of Yang Internet Addiction Questionnaire: an explanatory factor analysis. International Journal of High Risk Behaviors and Addiction 2015; 4:e21560. S6. Hawi NS, Blachnio A, Przepiorka A. Polish validation of the Internet Addiction Test. Computers in Human Behavior 2015; 48:548 553. S7. Guan NC, Isa SM, Hashim AH, et al. Validity of the Malay version of the Internet Addiction Test: a study on a group of medical in Malaysia. Asia-Pacific Journal of Public Health 2015; 27:NP2210-9. S8. Fernández-Villa T, Molina AJ, García-Martín M, et al. Validation and psychometric analysis of the Internet Addiction Test in Spanish among college. BMC Public Health 2015; 15:953. S9. Dhir A, Chen S, Nieminen M. Psychometric validation of Internet Addiction Test with Indian adolescents. Journal of Educational Computing Research 2015; 53:15 31. S10. Ahmad M, Alzayyat A, Al-Gamal E. The factor structure of the Internet Addiction Tool with university in Jordan. Issues in Mental Health Nursing 2015; 36:725 731. S11. Tsimtsiou Z, Haidich A-B, Kokkali S, et al. Greek version of the Internet Addiction Test: a validation study. Psychiatric Quarterly 2014; 85:187 195. S12. Sung M, Shin Y-M, Cho S-M. Factor structure of the Internet Addiction Scale and its associations with psychiatric symptoms for Korean adolescents. Community Mental Health Journal 2014; 50:612 618. S13. Pontes HM, Patrão IM, Griffiths MD. Portuguese validation of the Internet Addiction Test: an empirical study. Journal of Behavioral Addictions 2014; 3:107 114. S14. Karim AKMR, Nigar N. The Internet Addiction Test: assessing its psychometric properties in Bangladeshi culture. Asian Journal of Psychiatry 2014; 10:75 83. S15. Watters CA, Keefer KV, Kloosterman PH, et al. Examining the structure of the Internet Addiction Test in adolescents: a bifactor approach. Computers in Human Behavior 2013; 29:2294 2302. S16. Lee K, Lee H-K, Gyeong H, et al. Reliability and of the Korean version of the Internet Addiction Test among college. Journal of Korean Medical Science 2013; 28:763 768. S17. Lai C-M, Mak K-K, Watanabe H, et al. Psychometric properties of the Internet addiction test in Chinese

adolescents. Journal of Pediatric Psychology 2013; 38:794 807. S18. Hawi NS. Arabic validation of the Internet Addiction Test. Cyberpsychology, Behavior, and Social Networking 2013; 16:200 204. S19. Faraci P, Craparo G, Messina R, et al. Internet Addiction Test (IAT): which is the best factorial solution? Journal of Medical Internet Research 2013; 15:220 230. S20. Puerta-Cortés DX, Carbonell X, Chamarro A. Analysis of the psychometric properties of the Spanish version of Internet Addiction Test. Trastornos Adictivos 2012; 14: 99 104. S21. Conti MA, Jardim AP, Hearst N, et al. Evaluation of semantic equivalence and internal of a Portuguese version of the Internet Addiction Test (IAT). Revista de Psiquiatria Clinica 2012; 39:106 110. S22. Barke A, Nyenhuis N, Kroner-Herwig B. The German version of the Internet Addiction Test: a validation study. Cyberpsychology, Behavior and Social Networking 2012; 15:534 542. S23. Widyanto L, Griffiths MD, Brunsden V. A psychometric comparison of the Internet Addiction Test, the internetrelated problem scale, and self-diagnosis. Cyberpsychology, Behavior, and Social Networking 2011; 14:141 149. S24. Fioravanti G, Casale S. Evaluation of the psychometric properties of the Italian Internet Addiction Test. Cyberpsychology, Behavior, and Social Networking 2015; 18: 120 128. S25. Jelenchick LA, Becker T, Moreno MA. Assessing the psychometric properties of the Internet Addiction Test (IAT) in US college. Psychiatry Research 2012; 196:296 301.