Meta-analysis is a method to obtain a weighted average of results from various studies. In addition to pooling effect sizes, meta-analysis can also be used to estimate disease frequencies, such as incidence and prevalence. In this article we present methods for the meta-analysis of prevalence. We discuss the logit and double arcsine transformations to stabilise the variance. We note the special situation of multiple category prevalence, and propose solutions to the problems that arise. We describe the implementation of these methods in the MetaXL software, and present a simulation study and the example of multiple sclerosis from the Global Burden of Disease 2010 project. We conclude that the double arcsine transformation is preferred over the logit, and that the MetaXL implementation of multiple category prevalence is an improvement in the methodology of the meta-analysis of prevalence.

Depression and anxiety (internalizing disorders) are the largest contributors to the non-fatal health burden among young people. This is the first meta-analysis to examine the joint efficacy of universal, selective, and indicated preventive interventions upon both depression and anxiety among children and adolescents (5–18 years) while accounting for their co-morbidity. We conducted a systematic review of reviews in Medline, PsycINFO and the Cochrane Library of Systematic Reviews, from 1980 to August 2014. Multivariate meta-analysis examined the efficacy of preventive interventions on depression and anxiety outcomes separately, and the joint efficacy on both disorders combined. Meta-regressions examined heterogeneity of effect according to a range of study variables. Outcomes were relative risks (RR) for disorder, and standardized mean differences (Cohen's d) for symptoms. One hundred and forty-six randomized controlled trials (46 072 participants) evaluated universal (children with no identified risk, n = 54) selective (population subgroups of children who have an increased risk of developing internalizing disorders due to shared risk factors, n = 45) and indicated prevention (children with minimal but detectable symptoms of an internalizing disorder, n = 47), mostly using psychological-only strategies (n = 105). Reductions in internalizing disorder onset occurred up to 9 months post-intervention, whether universal [RR 0.47, 95% confidence interval (CI) 0.37–0.60], selective (RR 0.61, 95% CI 0.43–0.85) or indicated (RR 0.48, 95% CI 0.29–0.78). Reductions in internalizing symptoms occurred up to 12 months post-intervention for universal prevention; however, reductions only occurred in the shorter term for selective and indicated prevention. Universal, selective and indicated prevention interventions are efficacious in reducing internalizing disorders and symptoms in the short term. They might be considered as repeated exposures in school settings across childhood and adolescence. (PROSPERO registration: CRD42014013990.)