Please find a detailed description of the method in the final report cited above. The survey was conducted in state schools throughout Switzerland. A pilot study was conducted in the canton of Zurich. The standardized questionnaire was Internet-based and conducted through laptop computers. Due to the multilingual culture in Switzerland, the questionnaires were translated into three languages - German, French and Italian. Sampling was based on a list from the Swiss Federal Statistical Office containing all state schools and classes in Switzerland. A stratified target sample was drawn. Stratification was based on geographic regions and the strata were the seven Swiss "great regions" and the 26 cantons. Based on the school size, a Probability Proportion to Size (PPS) cluster sampling approach was used to draw schools and classes. Several different levels of approval needed to be passed. First, the project team sought ethical approval from all cantonal ethics committees separately. Second, approval from each cantonal Ministry of Education was sought. Third, the selected schools were contacted through an invitation letter containing a description of the study and an approval letter from the cantonal Ministry of Education.
