In 2007, Polanczyk and colleagues2 completed the first comprehensive meta-analysis of the prevalence of ADHD among children and adolescents. They attempted to gauge the worldwide pooled prevalence of ADHD or HD by including 102 studies that consisted of 171,756 subjects 18 years and younger from around the globe and that used DSM or ICD criteria for diagnosis. They found the ADHD/HD worldwide pooled prevalence to be 5.29% based on significantly variable data.
In their analysis, the prevalence among studies varied primarily because of methodological differences, including diagnostic criteria used, sources of information, and adherence to the requirement that impairment be present to make a diagnosis. In fact, prevalence estimates based on DSM-IV were higher than those based on ICD-10. Interestingly, geographic origin played a limited role. Although prevalence estimates from Africa and the Middle East were lower than those from North America, there were no other significant geographic differences.
Erik Willcutt3 subsequently published a comprehensive meta-analysis to estimate the prevalence of ADHD based on criteria from DSM-IV. He included 86 studies of children and adolescents and 11 studies of adults. He also found wide variability in prevalence estimates between individual studies. He reported that the pooled prevalence estimate of ADHD was 5.9% to 7.1% for children and adolescents. This was the case whether ADHD was diagnosed through parent ratings on questionnaires, teacher ratings, or a best-estimate diagnostic procedure when full DSM-IV diagnostic criteria were applied. The pooled estimate in young adults was 5.0% and was based on self-report measures. When the methodology used to diagnose ADHD was controlled for, there were no significant differences in prevalence between countries or regions of the world.
In 2015, Thomas and colleagues4 published a meta-analysis that consisted of 175 eligible studies over a 36-year period worldwide. They demonstrated an overall pooled prevalence of 7.2% and found that prevalence estimates for ADHD were lower when DSM-IIIR was used, compared with DSM-IV, and when studies were conducted in Europe, compared with North America.
In 2015, Polanczyk and colleagues5 undertook a meta-analysis to determine the worldwide prevalence of various mental health disorders in children, including ADHD. Based on 41 studies conducted in 27 countries between 1985 and 2012, they found a pooled prevalence of ADHD of 3.4%. Notable variation among the studies was seen, which indicates that methodology, such as representativeness of samples and use of diagnostic interviews and impairment criteria, had a significant impact on heterogeneity rather than geographic location or year of data collection. In fact, no increase in the prevalence of ADHD over time was demonstrated.
Concern that changes in diagnostic criteria could affect accurate identification of ADHD led McKeown and colleagues6 to examine the effect of the change in diagnostic criteria from DSM-IV to DSM-5 based on parent and teacher reports of elementary school students in South Carolina and Oklahoma. Prevalence estimates based on DSM-5 criteria with an age of onset before age 12 were demonstrated to be higher than prevalence estimates based on DSM-IV criteria with an age of onset before age 7. Again, methodology affected prevalence estimates.
Dr. Jummani is Clinical Assistant Professor, Director of Residency Education and Training, and Medical Director, Department of Child and Adolescent Psychiatry, Long Island Campus, Child Study Center at Hassenfeld Children’s Hospital of New York at New York University Langone Medical Center. Ms. Hirsch is Graduate Trainee and Doctoral Candidate, Clinical Psychology, Fordham University, New York. Dr. Hirsch is Associate Professor, Vice Chair for Clinical Affairs, Department of Child and Adolescent Psychiatry, and Medical Director, Child Study Center at Hassenfeld Children’s Hospital of New York at New York University Langone Medical Center, New York. The authors report no conflicts of interest concerning the subject matter of this article.
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