Statistical analysis
REGRESSION, DELETION
All analyses were performed using the software R [In order to identify the final set of explanatory variables, all variables with a significant result in the univariate analyses were included in the multivariate modelling process. In a second step, following the statistical principle of parsimony, we used a forward and backward deletion algorithm based on the Akaike criterion and, thereby, removed stepwise all non-significant variables. Hence, the final models do not comprise all variables which were significant in the univariate analysis. The reported ORs are not adjusted except in the final models or when otherwise stated. We used Poisson regression models to compare the number of barriers perceived by parents of children, parents of adolescents, and adolescents themselves. The significance level was set to α = 0.05.