Worldwide, 340 million people are affected by depression, with high comorbid, social and economic costs.
To identify potential predictors of effect in prevention programmes.
A meta-analysis was made of 69 programmes to reduce depression or depressive symptoms.
The weighted mean effect size of 0.22 was effective for different age groups and different levels of risk, and in reducing risk factors and depressive or psychiatric symptoms. Programmes with larger effect sizes were multi-component, included competence techniques, had more than eight sessions, had sessions 60–90 min long, had a high quality of research design and were delivered by a health care provider in targeted programmes. Older people benefited from social support, whereas behavioural methods were detrimental.
An 11% improvement in depressive symptoms can be achieved through prevention programmes. Single trial evaluations should ensure high quality of the research design and detailed reporting of results and potential predictors.