2.4. Data Collection
MAY
The baseline survey was conducted at the beginning of the school year (August 2016) and included 5201 students, of which 4577 responded to the questionnaire (response rate = 88.0%). The first follow-up was conducted at the end of the school year (May 2017) and included 4512 students, of which 3426 responded to the questionnaire (response rate = 75.9%) (