Sample-based prospective panel survey Survey design: Mixed mode (CATI interview & written questionnaire) Population (1st cohort TREE1): Youth who have completed compulsory school in 2000. Sample design: stratified sample; Sample size: valid sample at outset (2001): 6,343; Panel design: base survey (PISA) in 2000, 10 panel waves conducted in 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2010, 2014, 2019/20; further panel waves planned at 5-years intervals. Field work: Polling institute Population (2nd cohort TREE2): Youth who have completed compulsory school in 2016. Sample design: stratified sample; Sample size: valid sample at outset (2001): 8,429; Panel design: base survey (ÜGK) in 2016, annual panel waves from 2017 to 2022, further panel waves planned; Field work: Polling institute