The questionnaires were distributed to a total of 6198 parents of children from 16 schools, out of which 4179 parents consented and completed the questionnaire. 270 questionnaires were filled in, but without signing the consent forms. These were excluded from the analysis. A total number of 3909 children were therefore used for final analyses. These included 1990 children aged 6-7 years and 1919 children aged 13-14 years