Background: Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder estimated to affect approximately 5-7% of children and adolescents and 2-5% of adults. Estimates of the prevalence of the disorder vary widely around the world and between studies, most likely due to methodological differences between studies. To generate the best evidence and therefore decisions in healthcare, it is important to summarise only the highest quality and unbiased literature. To date, only one comprehansive systematic review, covering children, adolescents and adults worldwide has critically appraised the included research on the prevalence of ADHD.
Objectives: To critically appraise studies reporting the prevalence of ADHD using a valid tool, in order to assess the likelihood of bias in their design, conduct and analysis.
Methods: From a pool of 266 studies reporting the prevalence of ADHD, we identified 94 studies reporting the point prevalence of a clinically acquired diagnosis of ADHD, grouped them accordnig to the study design and developmental period of the subjects, and critically evaluated them for risk of bias using the selected tool. We took into account multiple sources of bias and adapted the tool's rating scheme to the Cochrane RoB-2 tool for randomized trials.
Results: Currently, the most appropriate tool for critically evaluating studies reporting the prevalence of disorders and diseases is The Joanna Briggs Institute Critical Appraisal Tool. As many as 57 studies (60,6%) reporting the prevalence of clinically diagnosed ADHD are highly biased and only six studies (6.4%) have a low risk of bias. The highest quality studies are the one- and two-stage clinical studies, but it is in these that the high risk of bias is most often introduced.
Conclusions: Much of the evidence on the prevalence of ADHD cannot be fully trusted. It is important that systematic reviewes and meta-analysts critically appraise research, and summarise only the highest quality literature to generate the best evidence in healthcare. The approach to critical appraisal of research needs to be structured, carefully thought out and clearly presented.
|