Eligible studies were peer reviewed randomised controlled trials (RCTs) where adult participants with current symptoms of depression were assigned to either a peer support intervention or a usual care or psychotherapy control condition. Symptoms were required to be measured before and after the intervention in both peer support and control groups.
In the included studies, the mean age of participants ranged from 20 to 74 years and the proportion of female participants ranged from zero to 100%, where reported. Participants were highly heterogeneous and included women in the perimenopause, with young children at home or postpartum, males with HIV, either gender with cancer, caregivers of sick patients and elderly patients after admission for psychiatric care. Control groups received either usual care or group cognitive-behavioural therapy (CBT). Depressive symptoms were measured by the Beck Depression Inventory (BDI), Centre for Epidemiological Studies Depression Scale, Zung Self-Rating Depression Scale, Hamilton Rating Scale for Depression (HRSD) and the Edinburgh Postnatal Depression Scale. Peer support group interventions ranged from once a week for nine months to 12 sessions weekly; one intervention used a telephone peer mentor for 10 weeks.
Two reviewers selected studies for the review. Discrepancies were resolved by discussion and consensus.