The reference population are all classes from grade 5 to 9 in public schools in Switzerland. In some cantons these grades are called “7th grade H” (HarmoS) to “11th grade H” (HarmoS).
The cluster sampling method is applied in order to randomly select study participants; schoolchildren are the basic units and classes are the clusters. The sample of school classes is stratified by canton.
The participants complete the questionnaire in the classroom during a regular lesson (45 minutes). The participation in the survey is voluntary and the participants’ responses are strictly anonymous.
In 2022, 857 5th to 9th grade classes (7th to 11th grade HarmoS) were randomly selected for participating in the national study (response rate = 74.2%). The final national sample comprises 9345 schoolchildren aged 11 to 15.
