Attention-deficit/hyperactivity disorder (ADHD) is among the most prevalent mental disorders in children and adolescents, persisting into adulthood in approximately half of cases. While reliable prevalence estimates are essential for planning public health interventions, high-quality data remain scarce. This dissertation provides a comprehensive systematic review and meta-analyses of ADHD prevalence across age groups and regions, assessing the impact of methodology on prevalence estimates.
We conducted a series of systematic reviews with meta-analyses of ADHD prevalence in Europe and worldwide, including observational, cross-sectional, and clinical studies of the general population with a clinically confirmed diagnosis of ADHD defined according to ICD or DSM criteria. Analyses were performed in the R environment. Risk of bias was assessed using an upgraded JBI tool.
The first systematic review identified 117 studies, with 103 were included in the final meta-analysis. Estimated pooled prevalence differed substantially by study design: register studies 1.6% (95% CI: 0.9–3.0), survey-based studies 5.0% (95% CI: 2.9–8.6), one-stage clinical studies 4.2% (95% CI: 2.9–6.0), and two-stage clinical studies 4.8% (95% CI: 4.0–5.8). Heterogeneity was high across all analyses. Temporal analyses showed higher prevalence estimates in two-stage clinical studies of preschool children before 2010, and higher estimates after 2010 in one-stage clinical and survey-based studies among school-aged children, as well as in register studies among adults.
The second systematic review included 12 studies reporting the prevalence of pharmacologically treated ADHD. Across studies reporting age-specific data, the pooled prevalence was 65.8%, with extremely high heterogeneity. Prevalence varied by age, increasing from preschool children (20.4%) to school-aged children (77.8%), adolescents (77.5%), and adults (82.6%). Including all studies, the pooled prevalence was 73.4% (95% CI: 63.4–81.5), again with substantial heterogeneity.
These findings highlight the substantial influence of methodological approaches, diagnostic criteria, and data sources on ADHD prevalence rates.
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