In the most recent Diagnostic and Statistical Manual of Mental Disorders, DSM-5, the age of onset criterion for
attention-deficit/hyperactivity disorder (ADHD)
was changed from 7, where it was placed in DSM-IV, to 12.

The writers said they changed the age to reflect the importance of clinical presentation during childhood for accurate diagnosis, while also acknowledging the difficulties in establishing precise childhood onset retrospectively. A recent paper in the Journal of the American Academy of Child and Adolescent Psychiatry says it has validated that decision.

Using data from a nationally representative sample of youth who participated in the National Health and Nutrition Examination Survey (NHANES), a group of researchers led by Dr. Kathleen Merikangas of the National Institute of Health Intramural Research Program, evaluated symptoms of ADHD and its subtypes in 1,894 participants aged 12-15 years based on parent reports of symptomatology.

They concluded that levels of severity, functional impairment, and patterns of comorbidity among the additional 3.46% of children who met all of the ADHD criteria except age of onset under 7 were comparable with those of other mental and behavioral disorders.

Although raising the age of onset criterion in DSM-5 from 7 to 12 generated an increase in the prevalence of all subtypes of ADHD, the greatest increase was found for inattention, which tends to have a later onset than symptoms of hyperactivity that emerge earlier in development. Dr. Merikangas noted that youth with the inattention subtype of ADHD are less likely to be recognized and treated because their problems may be less apparent at school and at home.

These findings highlight the importance of systematic study of diagnostic criteria in representative samples of the general population.