TRAILS has followed (pre-) adolescents from about age 11 years onwards. At the time the original cohort profile1 was written, the population cohort of TRAILS were about 16 years old; by now they have entered adulthood. Likewise, the age of the clinical cohort of TRAILS changed from about age 13 to about age 19. The incidence of psychiatric disorders is high in late adolescence and early adulthood, which indicated diagnostic interviews to assess psychiatric disorders and their age at onset, as well as detailed, registry-recorded data on psychiatric care utilization. Furthermore, developmental challenges change over time, which affects the factors and measures that are most relevant at a particular age. Biologically, the cohorts have matured from pre-adolescents into adults; regarding social factors, the focus in TRAILS has gradually shifted from parents and school to entry into the labour market and family formation. A final reason for the (partly) new data collection was the huge increase in genome-wide association studies and other collaborative gene-finding efforts, for which TRAILS’ excellent phenotypic data have great potential value.
