Table 2.

Definition of the variables Substance use and Problematic social networking site usage (PSNSU)

Variable	Question
Substance use	Have you drunk an alcoholic beverage at least once in the last month? (Yes/No)
	Have you drunk an energy drink at least once in the last month? (Yes/No)
	Have you smoked at least once in the last month? (Yes/No)
PSNSU	Do you ever stay up late and get up early in order to spend more time on social networking sites (Facebook, Netlog, Twitter, ...)? Never/Rarely/Sometimes/Often/Always)
	Do you feel anxious if you cannot connect to the social network for a while? (Never/Rarely/Sometimes/Often/Always)
	Have you ever spent more time on social networking sites than you had intended? (Never/Rarely/Sometimes/Often/Always)
	Have you ever neglected homework, sports activities, time with friends, and so on, in order to spend more time on social networks? (Never/Rarely/Sometimes/Often/Always)
	How often do you try to cut down the amount of time you spend on social networks and fail? (Never/Rarely/Sometimes/Often/Always)
	Have you ever thought, ‘I’ll carry on just for a few more minutes’ when on social networks? (Never/Rarely/Sometimes/Often/Always)