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The epidemiological rates for Attention Deficit Hyperactivity Disorder (ADHD) vary considerably throughout the world. This is thought to be due to environmental and behavioral changes, in addition to differences in diagnostic criteria used throughout the world.
It is more common in boys than in girls. As it is diagnosed in childhood and the symptoms may improve with time, the prevalence is higher in children than in adults.
The incidence of ADHD in school-aged children in the United States (US) is approximately 3-7%, which is around 1 in 20 children affected. The prevalence varies considerably according to the race and ethnic origin of the individual - children of Mexican background appear to be at lower risk.
One study that compared children with ADHD from 1998 to 2009 found that the rates of the condition seem to be increasing with time. For example, the number of children diagnosed with the condition rose to 7-9%. Additionally, the prevalence of ADHD in children with family incomes below the poverty level increased to 10-11%.
The incidence of ADHD in the United Kingdom (UK) is less than 1%, which is considerably less than that in the US. This difference is thought to be associated with both environmental factors and the heterogeneity of the condition itself. Additionally, the diagnostic criteria to be diagnosed with ADHD in the UK may be stricter than those used in the US, which may contribute to the differences in recorded epidemiological rates.
The prevalence of ADHD appears to vary considerably throughout different regions of the world. It is highest in South America, North America and Africa whilst lower prevalence rates have been noted in the Middle East, Asia, Australia, and Europe. Importantly, there are various factors that may contribute to the differences in prevalence in these areas.
Children with ADHD appear to be at a higher risk of developing conduct and substance abuse problems in adolescence and adulthood in comparison to children who are not affected. They also may have more difficulty in academic activities, social engagement and finding employment. This has the potential to affect quality of life and may also be associated with a higher risk of suicide, although exact morbidity and mortality rates have not been established.
According to the DSM-V diagnostic criteria, ADHD involves the presentation of several inattentive or hyper-impulsive symptoms before the age of 12. Therefore, the age of onset is in childhood and the symptoms may persist or fade after this point. For this reason, the prevalence is higher in children and lower in adults. Approximately 1 in 6 children with ADHD will maintain the full diagnosis with persistent symptoms into adulthood, and most children will continue to experience residual symptoms.
ADHD is 3-5 times more common in young boys than girls. However, the sex ratio tends to approach equilibrium in adulthood as the symptoms of more boys than girls usually improve. Girls with ADHD are typically more affected by the inattention type of the condition.