Monitoring adolescent health behaviours and social determinants cross-nationally over more than a decade: introducing the Health Behaviour in School-aged Children (HBSC) study supplement on trends

Young people are among the major driving forces of society’s development. They are the capital on which tomorrow's world is built. It is not the young people per se that enhance tomorrow's quality of life but their ideas, creativity, motivation and energy to move things forward; these are all aspects that are closely intertwined with health and wellbeing. Young people's health and wellbeing is multi-faceted and several aspects contribute to it such as their physical condition, being overweight, injuries, physical activity, having a good relationship with their parents, not being bullied or stressed by school-related issues, safe sexual intercourse and—most of all—being free of physical or mental complaints and satisfied with life in general. It is one of this supplement's strengths to bring many of these aspects together in one volume.But where are we standing in terms of adolescent health and wellbeing and related factors? What can possibly or realistically be achieved in the near future? These questions are crucial for policy makers in charge of improving young people's health and wellbeing. However, in a world in which most if not all conditions were found to be relative, it is impossible to answer these questions without a ‘fixed point' or ‘stand point' for comparison. In this respect, this supplement offers two valuable anchors. First, all contributions include multiple countries. This allows to see where a given country is standing in comparison to the neighbouring countries or to countries in different regions of Europe or even overseas. Second, all contributions include multiple survey years. This allows the comparison of a given age group, e.g. 15-year-olds, surveyed in 2010 with the same-aged peers living in the same country 4, 8, 12 or 16 years ago.Moreover, both aspects contribute to the assessment of differences in changes of prevalence (differences in trends) …