Randomised controlled trials (RCTs) that compared the effects of cognitive-behavioural group therapy to control (not further specified) as treatment for depression were eligible for inclusion if they had sufficient data to calculate an effect size. Eligible studies had to include participants aged over 18 years with a diagnosis of depression based on standardised criteria such as International Classification of Diseases, Diagnostic and Statistical Manual of Mental Disorders (DSM) III, DSM III-R, DSM IV, DSM IV-TR or Research Diagnostic Criteria. Studies were excluded if the cognitive-behavioural group therapy took place over the phone or the Internet. Primary outcomes of interest were level of depression and relapse rate from depression. There were further eligibility criteria based on study quality.
The included studies involved patients with mild to severe depression, chronic depression, seasonal affective disorder, residual depression, recovered recurrent depression, late life depression or major depressive disorder. The active and control interventions were behavioral activation, cognitive-behavioral analysis system of psychotherapy, cognitive-behavioral therapy, clinical management, cognitive therapy, interpersonal psychotherapy, light therapy, mindfulness-based cognitive therapy, minimal contact, delayed therapy, mutual support group, no treatment, pharmacotherapy, placebo pill, psychodrama and being on a waiting list.
Depression was measured using one or more of Beck Depression Inventory (English or Chinese version), Clinical Interview for Depression, Composite International Diagnostic Interview, DSM-III-R, DSM-IV, Geriatric Depression Scale, Hamilton Depression Rating Scale, Montgomery-Asberg Depression Rating Scale, Psychiatric status ratings, Research Diagnostic Criteria, Raskin Depression Scale, Structured Interview Guide for the Hamilton Rating Scale for Depression and supplementary Atypical Symptom subscale.
The mean age of participants ranged from 19.5 to 75.2 years. Cognitive-behavioural group therapy was conducted in groups of six to 10 people, generally by experienced therapists. Therapy sessions usually involved use of a therapy manual. Sessions usually lasted for one hour per week for eight to 12 weeks. Many studies involved take-home assignments.
Two reviewers independently selected the studies for inclusion. The authors do not state how discrepancies were resolved.