Is ADHD overdiagnosed? What the debate and the birthday studies say

Whether ADHD is overdiagnosed is a question researchers genuinely disagree about, and the evidence points in more than one direction. The strict meaning of "overdiagnosis" is children without ADHD being systematically and wrongly diagnosed, and to show it, false positives must substantially exceed false negatives. ADHD has been controversial since the 1970s, yet most healthcare providers accept it as a genuine disorder, at least for people with severe symptoms.

One line of evidence concerns birthdays. Studies from several countries describe a "relative-age effect": children who are young for their school year are more likely to be diagnosed and treated. A summary of these studies reports that boys born in December, where the school cut-off was December 31, were 30 percent more likely to be diagnosed and 41 percent more likely to be treated than boys born in January. Some researchers read this as evidence that diagnosis is prone to subjective judgement.

A second line says the opposite. Underdiagnosis has been discussed for adults, girls and poorer communities, and as few as 11 percent of adults with ADHD are estimated to receive an assessment. In 2014 Keith Conners, an early advocate for recognition of the disorder, spoke out against overdiagnosis, while a literature review the same year indicated that ADHD is underdiagnosed in adults.

Both can be true at once: the problem may be different from place to place and from person to person. This lesson describes the debate rather than settling it.