Summary: We believe the best data is for the UK is from the Lancet and NICE giving a childhood incidence rate of 5% and an adult incidence rate of 3-4%. That provides for a total estimate of 2.6million people in the UK with ADHD (708,000 children, 1,9m adults)
Childhood ADHD: In the UK, a research survey of 10,438 children between the ages of 5 and 15 years found that 3.62% of boys and 0.85% of girls had ADHD [Journal of Attention Disorders]. Global prevalence is considered to be between 2 and 7% with an average of 5%. [The Lancet]. The challenge for getting an exact incidence is that different countries, organisations, and professionals draw the line in different places for where they consider impairment to start, and therefore where they consider naming ADHD. Research conducted in Newcastle showed prevalence of 11% when asking about the symptoms but not looking for impairment. Then with impairment they found 6.7% with moderately low impairment, 4.2% for moderate impairments, and 1.4% for severe pervasive impairment. [European Child & Adolescent Psychiatry]. Regarding the gender split (roughly 4:1 boys:girls) there is an active discussion about whether female ADHD is under-diagnosed and if so the reasons for that.
Adult ADHD: ADHD changes with age (see below). It is thought that some children no longer have impairments; however, the majority, around 65%, retain some impairments in adulthood. The same study estimated prevalence of adult ADHD at 4.4%. [The American Journal of Psychiatry]. The UK Nice guidelines provide for an adult incidence rate of between 3 and 4%.
UK Population Estimate (2022)
(See below for Devolved Nations)
We have taken the Office of National Statistics population estimate from 2022 and used the childhood and adult ADHD incidence rates to extrapoloate out the likely number of individuals with ADHD.
* 15-19 age group split proportionally between children (under 18) and adults (18 and above) to give a weighted average incidence rate.
Devolved Nations ADHD Estimates
Extrapolating the figures above for the devolved nations. 2022 population data above is divided using the percentage split from ONS data on the devolved nation population sizes.