Depression in adolescence is important for a number of reasons. First, there is a high risk of recurrence in adulthood. Evidence from both clinical1 and community2 studies finds that adolescents with depression are more likely to have depression as adults. For example in Lewinsohn's Oregon study2 45% of 16 year olds with depression had a recurrence before the age of 23 (odds ratio 3.2 compared to no disorder). Second, once a person has had an episode of depression, it seems that future episodes are easier to provoke.3 In other words, successfully preventing the first episode of depression in adolescence might have much greater public health benefit than preventing recurrent episodes in adulthood. Third, adolescence is a critical period of life and can interfere with educational attainment and have detrimental effects on future occupation and the stability of future relationships4. Finally, self-harm is common in young people with depression5 and is associated with a substantial risk of suicide.

We propose to study depression at age 17 years in the Avon Longitudinal Study of Parents and Children (ALSPAC), a large birth cohort based in Bristol. Results from the ONS Longitudinal study suggest that the peak incidence of depression and anxiety occurs in young people6 in contrast to the prevalence that is higher in middle age. Depression has been measured before in ALSPAC, and the last occasion was at 15. However, the rates of depression are increasing rapidly at this age and the current proposal will allow investigation of a number of hypotheses by carrying out an assessment of depression at 17 years. It will also allow us to investigate psychological vulnerability factors for depression.