Table 1.

Variables measured in the questionnaire.

Factor	Operational variable
School level
School	Coded: 1, 2, 3 or 4
Individual/student level
Socio-demographic characteristics
Ethnicity*	Dutch, Moroccan, Turkish, Surinamese, Netherlands Antilles, other.
Socio-economic status*	Family affluence scale (FAS) [39]
School level*	Level 1 (‘VMBO’) to level 3 (‘VWO’)
Age*
Gender*	M/F
Behaviour
Ever alcohol use*	Yes/No
Recent alcohol use*	Yes/No
Frequency of recent alcohol use*	‘Number of times ever’/‘Number of times per month’
Ever smoked*	Yes/No
Active smoker*	Yes/No
Frequency of smoking*	‘Number of times per week’/‘Quantity per week’
Ever cannabis use*	Yes/No
Recent cannabis use*	Yes/No
Frequency of cannabis use*	‘Number of times ever’/‘Number of times per month’
Breakfast habits*	Number of days per week
Fruit consumption*	Portions per week
Vegetable consumption*	Number of days per week
Physical activity*	At least on average one hour a day moderate to intense physical activity
Recent bullying*	More than once per month
Recent, frequent bullying*	More than once per week
Recent being bullied*	More than once per month
Recent, frequent being bullied*	More than once per week
Ever had intercourse*	Yes/No
Age of first intercourse debut*	Age of student
Contraceptive use behaviour*	Range from ‘Always’ to ‘Never’ (5 point Likert scale)
Ever had STD*	Yes/No/Unsure
Time spent watching television*	Hours per week
Time spent on pc/internet*	Hours per week
Compulsive pc/internet use	Compulsive internet use scale (CIUS) [40]
Time spent (online) gaming*	Hours per week
Compulsive (online) gaming	Videogame addition test (VAT) [41]
Health outcome
Physical health*	Body mass index (BMI)
Psychosocial health	Strengths and difficulties questionnaire (SDQ)* [42, 43]
	Self efficacy measure [44]

*Variables directly based on the Dutch HBSC questionnaire.