The BIOS study investigated the additive effects of dimensional/categorical psychopathology, circadian/sleep, cognitive, environmental, and biological factors associated with the development of mood disorders. From 2001, the study recruited parents diagnosed with Bipolar Disorder (BP), as well as parents without a diagnosis of BP (controls), who had children between the ages of 2 and 18 years old. Except for children with a condition that impeded their participation in the study (e.g., mental retardation), offspring from each family were included as participants. In total, the study recruited around 600 parents, 900 offspring, and 100 third-generation participants (offspring of offspring). Participants repeated assessments approximately every two years for 20 years.