The study generally involves about 3,000 adults aged 15 years and about 1,000 children and adolescents aged 7-15 years (e.g. Fridberg 1989, 1994, 2000, Bille etai. These indicators are of particular interest in a nature/forest context - although the latter is a good example of an indicator/variable which is not very precise as it combines numerous settings/reasons for the activity. Finally, it is worth mentioning, that some questions/indicators have been slightly changed over time, which makes comparisons over time uncertain for some aspects.