The following variables were extracted into pre-defined excel spreadsheets: DOI/PMID, author, publication year, country of study, study design (birth cohort, cross-sectional, incidence studies, all representative of the general population), name of the cohort (if available), ICD/DSM diagnostic criteria, onset definition (first symptoms, first diagnosis, first hospitalisation), a specific type of mental disorder, sample age range, number of participants, number of cases developing incident mental disorders. Age at onset of mental disorders was extracted as available in each of the included studies (see statistics). Data extraction was performed independently by the same pairs of authors who performed the literature screening.
