Reply to reviewersReviewer #1 Comment 1: The aim of the study was to investigate the relationships between Problematic Internet Use (PIU) and time spent online, online activities and psychopathology, by taking cross-cultural and gender differences into account. Additionaly it was aimed to explore the prevalence of PIU among European Internet users according the 5593 responding internet users. The topic is timely and interesting.It is not clearly explained if problematic gaming, gambling and pornography are subdimensions of Problematic Internet Use (PIU) or different independent variables. Answer 1:We provided some additional information on page 1: "Therefore, PIU represents generalized PIU (Davis, 2001) and can include several specific uses, such as online gaming, gambling or pornography use (Laconi, Tricard, & Chabrol, 2015).".Comment 2: Which gap in the literature will be filled through this research, in other words what is the value added to the literature by this paper?Answer 2: We added additional information regarding this thanks to this comment, as follows: "Cross-cultural studies allow a better understanding of results given the use of the same methodology, timeline or statistical analysis. However, few cross-cultural studies have been performed on PIU, despite it being an international health issue. To our knowledge, only one cross-cultural study explored PIU among 989 adults of four European countries (Sariyska et al., 2014), the others being focused on adolescents, and none exclusively among European users. PIU has been the subject of many studies since the last decade, but there is a need for cross-cultural empirical research.". Comment 3: The possible reasons of the differences between countries based on the results of the study need to explained.Answer 3: More explanation has been provided in the discussion section and the second paragraph of this section begins by "Apart from the question of whether PIU as a phenomenon is on the increase, it is fascinating that comparing the countries we investigated, startling differences in the numbers of problematic users were found. Further research is *Response to Reviewers needed to determine whether a stable pattern emerges and what the reasons for these differences may be.".Besides, in the limitations section, we added: "Cultural background may be a weaker predictor of online behavior than age of onset for Internet use or participation in specific online communities. It can be argued that the Internet is facilitating the spread of new trends worldwide at a much faster rate than before, but also that it creates an international community in its own right, which is evident with the community of online gaming or social media.". Comment 4: The conclusion part is not satisfactory, also implications are missing. Answer 4:The conclusion has been modified. As all the reviewers suggested, an Implication section has been added.Comment 5 : Although the researchers tried to sample all ages, 2/3 of it is university students which can dominate the sample and may lead to ...

Objectives: The nine-item Problematic Internet Use Questionnaire (PIUQ-9) is a brief self-report screening instrument for problematic internet use. The main objective of the present study was to explore the psychometric properties of the PIUQ-9 among nine different language-based samples of European internet users (Italian, German, French, Polish, Turkish, Hungarian, English, and Greek). Methods: The total sample comprised 5,593 internet users (38.1% men), aged between 18 and 87 years ( M = 25.81; SD = 8.61). Via online recruitment, participants completed the PIUQ-9, the Brief Symptom Inventory (BSI) and items about time spent online. Results: Confirmatory factor analysis demonstrated that the bifactor model with one general factor (i.e., general problem) and two-specific factors (i.e., obsession and neglect + control disorder) yielded acceptable or good fit indices in all subsamples except for one. The common variance index in the bifactor model indicated that the general problem factor explained from 57.0 to 76.5% of common variance, which supports the presence of a strong global factor. According to the multiple indicators multiple causes (MIMIC) model, psychiatric symptoms had a moderate-to-strong direct effect on the general problem factor in all subsamples, ranging from β = 0.28 to β = 0.52 supporting the construct validity of the scale. Furthermore, in a majority of the subsamples, time spent online during the weekend had considerably higher effect sizes on the general problem factor than time spent online during weekdays. Conclusion: The present study highlights the appropriate psychometric properties of the PIUQ-9 across a number of European languages and cultures.

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