This review of reviews presents an empirically based set of mean effect size distributions for judging the relative impact of the effects of universal mental health promotion and prevention programs for school-age youth (ages 5 through 18) across a range of program targets and types of outcomes. Mean effect size distributions were established by examining the findings from 74 meta-analyses of universal prevention and promotion programs that included more than 1100 controlled outcome studies involving over 490,000 school-age youth. The distributions of mean effect sizes from these meta-analyses indicated considerable variability across program targets and outcomes that differed substantially from Cohen's (1988, Statistical power analysis for the behavioral sciences (2nd ed.)) widely used set of conventions for assessing if effects are small, medium, or large. These updated mean effect size distributions will provide researchers, practitioners, and funders with more appropriate evidence-based standards for judging the relative effects of universal prevention programs for youth. Limitations in current data and directions for future work are also discussed.
Keywords: Effect sizes; Meta-analysis; Universal prevention; Youth.