Maartje Boer

SMU AND ADHD-SYMPTOMS 133 5 accordance with the Declaration of Helsinki and were approved by the board of ethics of the Faculty of Social Sciences at Utrecht University (FETC16-076 Eijnden). Measures SMU Intensity Four items on the use of social network sites and instant messengers were used to measure SMU intensity (Van den Eijnden et al., 2018). Respondents were asked “Howmany times a day do you check social network sites?”, “How many times a week do you ‘like’ messages, photos, or movies from others on social network sites?”, “How many times a week do you send out a response to (or share) messages, photos, or movies from others on social network sites?”. Examples of social network sites were provided in the questionnaire (Facebook, Twitter, Instagram, Google+, or Pinterest). Respondents answered on a 7-point scale, where high values indicate high SMU intensity (1 = less than once a day and 7 = more than 40 times ). The fourth item referred to instant messenger use: “How many times a day do you send a message, photo or movie via your smartphone, via for example WhatsApp, Chat, SnapChat or SMS?” (1 = less than once a day and 7 = more than 80 times ). Factor loadings of all items ranged between 0.68 and 0.82 across all three waves. Cronbach’s α values were 0.86 (T1), 0.85 (T2), and 0.84 (T3). The original scale consisted of six items. Items “How many times a week do you post a message, photo, or movie, on social network sites?” and “How many times a day do you check your smartphone on messages, photo’s, or videos, via for example WhatsApp, Chat, SnapChat or SMS?” were excluded due to having factor loadings below 0.5, and high intercorrelation ( r = 0.70) with another item, respectively. SMU Problems The Social Media Disorder-scale was used to measure SMU problems (Van den Eijnden et al., 2016). The scale includes nine items corresponding to the nine diagnostic criteria for Internet Gaming Disorder according to the Appendix of the DSM-5 (American Psychiatric Association, 2013; Lemmens et al., 2015). These criteria entail preoccupation, persistence, tolerance, withdrawal, displacement, escape, problems, deception, and conflict, which