The Worldwide Prevalence of ADHD: A Systematic Review and Metaregression Analysis
Guilherme Polanczyk, M.D. Maurício Silva de Lima, M.D., Ph.D. Bernardo Lessa Horta, M.D., Ph.D. Joseph Biederman, M.D. Luis Augusto Rohde, M.D., Ph.D.
Objective: The worldwide prevalence estimates of attention deficit hyperactivity disorder (ADHD)/hyperkinetic disorder (HD) are highly heterogeneous.Presently, the reasons for this discrepancy remain poorly understood. The purpose of this study was to determine the possible causes of the varied worldwide estimates of the disorder and to compute its worldwide-pooled prevalence. Method: The authors searched MEDLINE and PsycINFO databases from January 1978 to December 2005 and reviewed textbooks and reference lists of the studies selected. Authorsof relevant articles from North America, South America, Europe, Africa, Asia, Oceania, and the Middle East and ADHD/HD experts were contacted. Surveys were included if they reported point prevalence of ADHD/HD for subjects 18 years of age or younger from the general population or schools according to DSM or ICD criteria. Results: The literature search generated 9,105 records, and 303 full-textarticles were reviewed. One hundred and two studies comprising 171,756 subjects from all world regions were included. The ADHD/HD worldwide-pooled prevalence was 5.29%. This estimate was associated with significant variability. In the multivariate metaregression model, diagnostic criteria, source of information, requirement of impairment for diagnosis, and geographic origin of the studies weresignificantly associated with ADHD/HD prevalence rates. Geographic location was associated with significant variability only between estimates from North America and both Africa and the Middle East. No significant differences were found between Europe and North America. Conclusions: Our findings suggest that geographic location plays a limited role in the reasons for the large variability of ADHD/HDprevalence estimates worldwide. Instead, this variability seems to be explained primarily by the methodological characteristics of studies.
(Am J Psychiatry 2007; 164:942–948)
ttention deficit hyperactivity disorder (ADHD) is characterized by pervasive and impairing symptoms of inattention, hyperactivity, and impulsivity according to DSM-IV (1). The World Health Organization (WHO) (2) usesa different name—hyperkinetic disorder (HD)—but lists similar operational criteria for the disorder. Regardless of the name used, ADHD/HD is one of the most thoroughly researched disorders in medicine (3). It has been associated with a broad range of negative outcomes for affected subjects (4, 5) and with a serious financial burden to families and society (6), which characterizes it as a majorpublic health problem (7). An understanding of the epidemiological aspects of ADHD/HD may provide insight into its distribution and etiology as well as information for planning the allocation of funds for mental health services (8). In past decades, investigators from all regions of the world have made substantial efforts to define the prevalence of the disorder. Several literature reviews havereported highly variable
rates worldwide, ranging from as low as 1% to as high as nearly 20% among school-age children (8, 9). Although the reasons for variability across studies remain poorly understood, it has been hypothesized that geographical and demographic factors are associated with it (10). Several investigators have suggested that prevalence rates in Europe were significantly lower thanrates found in North America (8, 11, 12). This hypothesis fueled the concern that ADHD/HD may be a product of cultural factors and promoted an enduring debate in the medical literature (8, 11, 12). Other experts have argued that the variability of ADHD/HD prevalence estimates may be best explained by the use of different case definitions and that no variability of the actual prevalence across...