The iBerry study is a population-based cohort study designed to investigate the transition from subclinical symptoms to a psychiatric disorder. Adolescents were selected based on their self-reported emotional and/or behavioral problems assessed by completing the strengths and difficulties questionnaire-youth (SDQ-Y) in their first year of high school. A total of 16,736 SDQ-Y questionnaires completed in the academic years 2014-2015 and 2015-2016 by students in the greater Rotterdam area in the Netherlands were screened. A high-risk group of adolescents was then selected based on the 15% highest-scoring adolescents, and a low-risk group was randomly selected from the 85% lowest-scoring adolescents, with a 2.5:1 ratio between the number of high-risk and low-risk adolescents. These adolescents were invited to come with one parent for a baseline visit consisting of interviews, questionnaires, neuropsychological tests, and biological measurements to assess determinants of psychopathology. A total of 1022 high-risk and low-risk adolescents (mean age at the first visit: 15.0 years) enrolled in the study. The goal of the iBerry study is to follow these adolescents for a 10-year period in order to monitor any changes in their symptoms. Here, we present the study design, response rate, inclusion criteria, and the characteristics of the cohort; in addition, we discuss possible selection effects. We report that the oversampling procedure was successful at selecting a cohort of adolescents with a high rate of psychiatric problems based on comprehensive multi-informant measurements. The future results obtained from the iBerry Study will provide new insights into the way in which the mental health of high-risk adolescents changes as they transition to adulthood. These findings will therefore facilitate the development of strategies designed to optimize mental healthcare and prevent psychopathology.
Keywords: Adolescents; Cohort study; Design; Epidemiology; High-risk; Psychopathology.