The RADAR participants were recruited from randomly selected high schools in the middle and west of the Netherlands and consist of two groups:
- RADAR Young: 497 adolescents of Dutch origin, who were 12 years old at the start of RADAR. Additionally, a group of 190 Moroccan adolescents was followed from age 12 until age 17. This group does no longer participate in the RADAR assessments.
- RADAR Old: 233 adolescents of Dutch origin, who were 15 years old at the start of RADAR.