There have now been many controlled studies of preventive mental health interventions for young people. For these studies to be useful, practitioners need to know whether the effects shown for a particular intervention are modest, moderate, or large.
Emily Tanner-Smith and colleagues summarised more than 400 mean effect size estimates from 74 meta-analyses that synthesised findings from many trials. All the trials were of programmes aimed at preventing problematic behaviour or emotional problems for young people aged 5-18. The results, published in Prevention Science, indicate that, with few exceptions, the median average effect sizes on various outcomes fell within the range of +0.07 to +0.16. The authors advise that these indicate the level of improvement that has been achieved to date and can serve as a benchmark for assessing the value of new findings.
The report also points out that prevention programmes yielded larger effects on knowledge than on actual behaviour. Providing information to increase knowledge (e.g., about the risks of drug use) is an important component of many programmes, but knowledge does not always correlate strongly with actual behaviour.
Source: Empirically Based Mean Effect Size Distributions for Universal Prevention Programs Targeting School-Aged Youth: A Review of Meta-Analyses (August 2018) Prevention Science