|Environmental variables/determinants related to dietary behaviors|
|Snack availability at home||
The home availability of the 28 snack items used in the FFQ.|
The constructs of these questions are based on valid questions from the European HELENA study .
Perceived peers’ snacking behavior, peers’ social support, social pressure, and subjective norm regarding healthy snacks.|
These items are based on valid and reliable items from the HELENA and ENERGY study [55, 59].
Parents’ modeling, rules at home, and monitoring in relation to snacks.|
The items are based on valid and reliable items from the HELENA and ENERGY study [55, 59].
|Personality traits/biological factors|
|Reward sensitivity and punishment sensitivity||
The Dutch child version of the Carver and White’s Behavioral Inhibition System (BIS)/Behavioral Approach System (BAS) - scale as developed by Franken and colleagues .|
The convergence and discriminant validity as well as the internal consistency of the BIS/BAS scale have been demonstrated [63–65].
The five-items subscale restraint from the Child Eating Disorder Examination Questionnaire (ChEDE-Q ).|
Research demonstrated the reliability and validity of the ChEDE-Q for examining eating pathology in youngsters from the general population  and in clinical samples of treatment seeking obese youngsters .
|Pubertal status||The Pubertal Development Scale  which is a five-item self-report questionnaire to ascertain pubertal status in adolescents.|
|Other measurements on nutrition behaviors|
|Total energy intake per day||An FFQ to estimate total dietary intake was developed and has been used in and adjusted for several target population from pre-schoolers to older women [51, 70, 71].|
|Adolescents’ meal patterns:||
The frequency of eating breakfast, lunch and dinner, the frequency of snacking, and the source from which they usually obtain the snacks.|
All questions originate from the validated questionnaires of the European HELENA study .
|Game behavior-related variables|
|Duration and frequency of game play||
Duration will be measured via a timeline separately for each day of the week. Frequency will be assessed by using a 7-point Likert scale from ‘almost never’ to ‘almost every day’. Respondents are asked to indicate how often they play games on any device.|
Both methods have been used in previous studies to measure game use .
|Preferences for game genres||This will be measured separately for computer/console games and smartphone/tablet games. For both categories a list of 13 game genres has been developed based on previous studies and current popular game genres [74, 75]. Given that new games and even new game genres arise every year, the list was updated to the current situation.|
|Game motivations||The Uses and Gratifications Questionnaire for game developed by Sherry et al. .|
The Game Engagement Questionnaire of Brockmeyer and colleagues .|
This validated instrument consists of 19 items from which a total Game Engagement Score can be derived in order to examine one’s involvement in games.
|Game addiction||A 7-item Game Addiction Scale  of which each item corresponds with one of the seven criteria for pathological gambling according to the DSM: salience, tolerance, mood modification, withdrawal, relapse, conflict and problems.|
|Smartphone and tablet use||Respondents will be asked to indicate whether they use a smartphone or tablet (yes or no). Given that our serious game can be played on either of these devices it is important to take into account previous experience with the devices.|
|Structural characteristics||Adolescents will be asked to indicate how important several structural characteristics of video games are for their game experience. King, Delfabbro & Griffiths  recently developed a list of game dynamics based on psychological structures. The researchers have analyzed games and made an overview of game dynamics that are engaging to game players, which they tested on a broad sample of various age groups.|