ADHD is estimated to affect about 6 to 7 percent of people aged 18 and under when diagnosed via the DSM-IV criteria. Hyperkinetic disorder when diagnosed via the ICD-10 criteria give rates of between 1 and 2 percent in this age group.
Children in North America appear to have a higher rate of ADHD than children in Africa and the Middle East - however, this may be due to differing methods of diagnosis used in different areas of the world. If the same diagnostic methods are used rates are more or less the same between countries.
Epidemiology of attention deficit hyperactive disorder Wikipedia
It is estimated that ADHD affects between 5.4-8.7% of children in Africa. Data quality however is not high.
A 2008 evaluation of the “KiGGS” survey, monitoring 14,836 girls and boys (age between 3 and 17 years), showed that 4.8% of the participants had an ADHD diagnosis. While 7.9% of all boys had ADHD, only 1.8% girls had it, too. Another 4.9% of the participants (6.4% boys : 3.6% girls) were suspected ADHD cases, because they showed a rate ≥7 on the Strengths and Difficulties Questionnaire (SDQ) scale. The number of ADHD diagnoses was 1.5% (2.4% : 0.6%) among preschool children (3–6 years old), 5,3 % (8.7% : 1.9%) at age 7–10 years, and had its peak at 7.1% (11.3% : 3.0%) in the age group of 11–13 years. Among 14 to 17 years old adolescents the rate was 5.6% (9.4% : 1.8%).
Rates in Spain are estimated at 6.8% among people under 18.
In the United States it is diagnosed in 2-16 percent of school children. The rates of diagnosis and treatment of ADHD are much higher on the east coast of the United States than on its west coast. The frequency of the diagnosis differs between male children (10%) and female children (4%) in the United States. This difference between genders may reflect either a difference in susceptibility or that females with ADHD are less likely to be diagnosed than males. Boys outnumber girls across all three subtyping categories, but the exact magnitude of these differences seems to depend on both the informant (parent, teacher, etc.) and the subtype. In two community-based investigations, conducted by DuPaul and associates, boys outnumbered girls by only 2.2:1 in parent-generated samples and 2.3:1 in teacher-based input.
Rates of ADHD diagnosis and treatment have increased in both the United Kingdom and the United States since the 1970s. This is believed to be primarily due to changes in how the condition is diagnosed and how readily people are willing to treat it with medications rather than a true change in the frequency. In the UK an estimated 0.5 per 1,000 children had ADHD in the 1970s, while 3 per 1,000 received ADHD medications in the late 1990s. In the UK in 2003, 3.6 percent of male children and less than 1 percent in female children had the diagnosis. In the United States the number of children with the diagnosis increase from 12 per 1000 in the 1970s to 34 per 1000 in the late 1990s, to 95 per 1,000 in 2007, and 110 per 1,000 in 2011. It is believed that the changes to the diagnostic criteria in 2013 from the DSM 4TR to the DSM 5 will increase the number of people with ADHD especially among adults.