In total 1,688 pupils (more or less between 12 and 18 years old) filled out a questionnaire during a common period at school. In selecting schools and classes for the sample, we aimed for a balanced representation of adolescents over the four educational systems and grades in Flanders.
An important advantage of this sampling design is that it produces a sample of adolescents across all social layers of society and from schools that differ in the socio-economic and cultural backgrounds of their pupils.