title: The worldwide prevalence of ADHD: a systematic review and metaregression analysis.
abstract: 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.
  
  
  METHODS
  The authors searched MEDLINE and PsycINFO databases from January 1978 to December 2005 and reviewed textbooks and reference lists of the studies selected. Authors of 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-text articles 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 were significantly 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/HD prevalence estimates worldwide. Instead, this variability seems to be explained primarily by the methodological characteristics of studies.
authors.affiliation: ADHD Outpatient Program, Child and Adolescent Psychiatric Division, Hospital de Clinicas de Porto Alegre, Federal University of Rio Grande do Sul, Rua Ramiro Barcelos, 2350, Porto Alegre, RS, Brazil 90035-003. gvp.ez@terra.com.br
authors.forename: Guilherme
authors.initials: G
authors.lastname: Polanczyk
authors.forename: Maurício Silva
authors.initials: MS
authors.lastname: de Lima
authors.forename: Bernardo Lessa
authors.initials: BL
authors.lastname: Horta
authors.forename: Joseph
authors.initials: J
authors.lastname: Biederman
authors.forename: Luis Augusto
authors.initials: LA
authors.lastname: Rohde
mesh_terms: D000293:Adolescent; D000349:Africa / Q000453:epidemiology; D001289:Attention Deficit Disorder with Hyperactivity / Q000453:epidemiology*; D002648:Child; D003431:Cross-Cultural Comparison; D039721:Diagnostic and Statistical Manual of Mental Disorders; D005060:Europe / Q000453:epidemiology; D005260:Female; D014943:Global Health; D006306:Health Surveys; D006801:Humans; D038801:International Classification of Diseases; D008297:Male; D008877:Middle East / Q000453:epidemiology; D009656:North America / Q000453:epidemiology; D015995:Prevalence; D012044:Regression Analysis; D012107:Research Design