Second, there is a critical need for prospective, longitudinal studies. Most existing longitudinal studies have begun in late adolescence or adulthood. However, a substantial proportion of mood disorders have already developed by mid-adolescence. Therefore, in order to further test the precursor and predisposition models, and to trace the developmental pathways between personality and depression, it is necessary to conduct longitudinal studies that start as early as possible in order to obtain a sufficient number of first-onset cases and avoid selection biases caused by excluding participants who already have a history of mood disorder at initial assessment.
