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What is ADHD and How Prevalent Is It?

ADHD is a complex, often misunderstood and misdiagnosed condition which is estimated to impact around


  • 5 to 7% of children worldwide.

  • 2 to 5% of adults worldwide. 


Depending on the diagnostic criteria used.

Defining ADHD from a Clinical Perspective

The Diagnostic and Statistical Manual of Mental Disorders 5th Edn (DSM-5) which is used in the USA and much of the rest of the world to provide a formal clinical framework for diagnosing ADHD classifies ADHD as:

"a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development".

Along with exceeding a threshold number of symptoms in either or both of these core areas of impairment the DSM-5 further specifies that

  • Symptoms have persisted for at least 6 months (for children to a degree which is incompatible with developmental level).

  • Several inattentive and/ or hyperactive-impulsive symptoms were present prior to the age of 12 years old.

  • Several inattentive and/ or hyperactive-impulsive symptoms are present in two or more settings (e.g. at home, school or work; with friends or relatives; in other activities.

  • There is clear evidence that the symptoms interfere with, or reduce the quality of, social, academic or occupational functioning.

  • Symptoms do not occur exclusively during the course of schizophrenia or another psychotic disorder, and are not better explained by another mental disorder (e.g. mood disorder, anxiety disorder, dissociative disorder, personality disorder, substance intoxication or withdrawal).

Formally Diagnosing ADHD

Currently there is no physical test or neurological screening process that  unequivocally confirms the presence of ADHD.

Instead a formal diagnosis of ADHD requires gathering and aggregating evidence in alignment with the DSM-5 classification of ADHD.  


This can only be performed by an appropriately qualified medical professional (in the UK usually a Psychiatrist or Paediatrician with specialist knowledge of ADHD).

An ADHD assessment will be made through evaluation of the severity and pervasiveness of symptoms, and associated level of functional impairment, in these two core areas of Inattention and Hyperactivity and Impulsivity.

For adults evidence is  additionally sought to ascertain the presence and prevalence of symptoms in childhood. 

The current National Institute for Health and Care Excellence (NICE) Guidelines for ADHD  stipulate that diagnosis should be made on the basis of

  • a full clinical and psychosocial assessment of the person 

  • a full developmental and psychiatric history

  • observer reports and assessment of a person's mental state

Additionally Structured Diagnostic Interviews and Ratings Scales such as the Conners' rating scales and the Strengths and Difficulties Questionnaire are often used to support the diagnostic process.

Sub-Types of ADHD

Depending on the relative predominance and symptom pattern of Inattentive v Impulsive/ Hyperactive symptoms one of three sub-types of ADHD may be diagnosed as follows :

  • ADHD Predominantly Inattentive Sub-Type

  • ADHD Predominantly Hyperactive/ Impulsive Sub-Type

  • ADHD Combined Sub-Type

In the simplest terms this amounts to ADHD with or without visible manifestations of hyperactivity.

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