The diverse ways depression changed in an economically diverse sample of over 1,000 young people traveling from age 18 to age 22: Notice from this chart that the vast majority of young people are happy both during their teens and as they emerge into their early twenties (red). Those teens with major depressive disorders are still battling their condition three years later (blue). But a reasonable percentage of moderately depressed teens become happier as they make the transition to adult life (yellow line)—although, granted, some do become more depressed.
Data from: Frye & Liem, 2011.