Assumptions used in estimating a population benchmark

The assumptions used in estimating a population benchmark for assessment, diagnosis and management of moderate-to-severe attention deficit hyperactivity disorder (ADHD) for children and young people aged 3-15 years of 50 per 100,000 population (all ages) per year are based on the following source(s) of information:

• epidemiological data on the prevalence/incidence of ADHD
• current practice on detection rate of ADHD in primary care
• published research on parent-training/education programmes in the management of children with conduct disorders and ADHD
• expert clinical opinion of the topic-specific advisory group, based on experience in clinical practice and literature review.

Epidemiological data

Prevalence estimates of ADHD are rare in the published literature, especially in relation to the diagnostic and statistical manual of mental disorders, 4th edition (DSM-IV) and ICD-10 (International classification of diseases and related health problems, 10th revision) criteria.

The prevalence of ADHD in people aged 5-15 years is based on the 1999 British Child and Mental Health Survey and is 3.62% in males and 0.85% in females^[1]. Applying these figures to the population of children and young people aged 3-15 years equates to an estimated overall prevalence of 2.27%.

Current practice

Data from GP practice systems are likely to underestimate the prevalence of ADHD.

IMS Disease Analyser database holds patient data from a sample of GP practice systems. Data was extracted to determine the prevalence and incidence of ADHD. This was done on the basis of Read codes that are suggestive of ADHD or notes in the records of a prescription for atomoxetine, dexamphetamine or methylphenidate.

Data from these databases suggest that the prevalence of diagnosed ADHD in the population of children and young people aged 3-15 years is around 0.7% and the incidence is around 0.05%.

These estimates are likely to be significant underestimates of both the numbers of children and young people with moderate-to-severe ADHD known to services (those with a diagnosis of ADHD) and the numbers of children and young people with moderate-to-severe ADHD in the general population (those diagnosed with ADHD and those with ADHD but undiagnosed).

For the purpose of this benchmark, and based on the opinion of the topic-specific advisory group, we have assumed that all these patients have either moderate or severe ADHD.

Published research

Not all children and young people referred for specialist assessment and diagnosis will have the diagnosis of ADHD confirmed. In an ADHD clinic that screened new referrals, just under 50% of those referred for assessment had the diagnosis of ADHD confirmed^[2].

Expert clinical opinion

The consensus opinion of the topic-specific advisory group was that the prevalence estimates from the 1999 British Child and Mental Health Survey are conservative estimates of ADHD in children and young people aged 3-15 years and should be considered to represent moderate-to-severe ADHD.

Not all children and young people who are referred for diagnosis and specialist assessment will have the diagnosis of ADHD confirmed. Based on their experience of clinical practice, the topic-specific advisory group agreed that around 50% of those referred would have the diagnosis of ADHD confirmed. The remaining 50% may have other conditions which may require intervention and/or onward referral.

Conclusions

Based on the epidemiological data and other information outlined above, it is concluded that 0.32% of the population of children and young people aged 3-15 years need referral to a service for the assessment, diagnosis and management of children and young people with moderate-to-severe ADHD, each year. This is based on the following assumptions:

• The population prevalence of moderate-to-severe ADHD in children and young people aged 3-15 years is 2.27%.
• The prevalence of moderate-to-severe ADHD in children and young people aged 3-15 years based on general practice data is estimated to be 0.7%.
• This means that the prevalence of diagnosed ADHD based on general practice data would need to more than treble (that is, increase by 224% or a factor of 3.24) to reach the population prevalence of moderate-to-severe ADHD.
• The incidence of diagnosed moderate-to-severe ADHD based on general practice data is 0.05%. Increasing this figure by the same amount (224% or a factor of 3.24) to the level required for the prevalence of diagnosed ADHD to reach the population prevalence gives a result of 0.16%.
• This adjustment of the incidence rate accounts for both under-recording of known cases of ADHD and underdiagnosis of ADHD.
• This represents only 50% of the numbers referred, as not all children and young people referred will have the diagnosis of ADHD confirmed. Adjusting for this would suggest that 0.32% of the population aged 3-15 years could be referred each year. This corresponds to around 50 per 100,000 population (all ages).

Therefore the population benchmark for assessment, diagnosis and management of moderate-to-severe ADHD in children and young people aged 3-15 years is estimated to be 50 per 100,000 population (all ages) per year.

Services for young people aged 3 to 17 years

The NICE commissioning guide on a service for the diagnosis and management of ADHD in adults includes services for the transition of young people aged 16-17 years into adult services.

An indicative benchmark rate is also offered for children and young people aged 3-17 years for those commissioners who wish to include young people aged 16 and 17 in their planning of services for children and young people. The same methodology has been used as outlined above, based on the following:

• The prevalence of ADHD in the population aged 16-17 years based on the 1999 British Child and Mental Health Survey has been estimated at 2.99% in males and 0.70% in females. The assumptions section of the NICE commissioning guide on service for the diagnosis and management of ADHD in adults outlines how this has been estimated. This equates to a prevalence of ADHD in the population aged 3-17 years of 2.21%.
• Patient data from GP practice systems suggests that the prevalence of diagnosed ADHD for the population aged 3-17 years is around 0.7% and the incidence is around 0.05%.
• Applying the same methodology outlined in this commissioning guide (increasing the diagnosed incidence by the difference between the diagnosed prevalence and population prevalence), the diagnosed incidence of ADHD in the population aged 3-17 years comes to 0.16% (increasing 0.05% by 216% or by a factor of 3.16). This represents only 50% of those referred (see above) which suggests that 0.32% of the population aged 3-17 years could be referred each year. This corresponds to a rate of 60 per 100,000 population (all ages) per year.

The population benchmark for a service for the diagnosis and management of ADHD in children and young people aged 3-17 years is estimated to be 60 per 100,000 population (all ages) per year.

Use the service for the diagnosis and management of ADHD in children and young people commissioning and benchmarking tool to determine the level of service that might be needed locally and to calculate the cost of commissioning the service using the indicative benchmark and/or your own local data.

References

1. Ford T, Goodman R, Meltzer H (2003) The British Child and Adolescent Mental Health Survey 1999: the prevalence of DSM-IV disorders. Journal of the American Academy of Child and Adolescent Psychiatry 42: 1203-11

2. Sayal K, Letch N, Abd S (2008) Evaluation of screening in children referred for an ADHD assessment. Child and Adolescent Mental Health 13: 41-6