Mood in the moment: a study protocol for embedding ecological momentary assessments into established longitudinal cohorts to examine depression in real time

Introduction Depression is a major global health challenge, with onset commonly occurring in youth. There is an urgent need to better understand the epidemiology of depression to facilitate better interventions and preventions that are person-specific and time-specific.

Long-term depression trajectories and ecological momentary assessment (EMA) can help address this need. Embedding EMA designs within established longitudinal cohorts offers a uniquely powerful approach to examine depression in both long- and short-term settings and to identify distal and proximal modifiable risk factors for depression.

Methods and analyses Our study will include ~450 participants from the Twins Early Development Study and ~250 participants from the Avon Longitudinal Study of Parents and Children (ALSPAC) who have depression trajectories data previously collected between late childhood and early adulthood. Participants will be recruited from four different depression trajectories in each cohort based on participants' prior symptoms.

They will undertake EMA surveys of depression, sleep, physical activity, substance use, diet, recent activities and social interactions three times a day for 6 weeks, with more detailed questionnaires at baseline, 2, 4 and 6 weeks.