Depressive symptoms increased across time, and model fitting revealed that a curvilinear function was adequate to describe these changes, with the shape of the curve differing across the sexes. Among males, depressive symptoms increased gradually at first, followed by a steeper increase in later adolescence, whilst among females, depressive symptoms increased more markedly in early adolescence before stabilizing as adulthood approached. The trajectories of depressive symptoms are largely consistent with previous reports. In particular, the rapid increase in symptoms, followed by a plateau, observed in females is similar to that observed in other population-based samples [3, 29–31]. Findings for males’ trajectories have been more varied, with some studies reporting consistently low levels of depressive symptoms [29, 30], others finding a shape similar to females in the current sample [3], or gradually decreasing symptoms [32, 33]. Consistent with previous studies [23, 24], initial levels of depressive symptoms are similar across the sexes; however, sex-specific mean symptom levels quickly diverge.
