Children With High IQs Get ADHD Diagnosed Later, Study Reveals

A new study reveals some of the most significant factors affecting the age at which attention-deficit hyperactivity disorder (ADHD) is diagnosed – and having a higher IQ is one of the traits associated with a later diagnosis.

The study team, led by researchers from the University of Western Ontario and Queen's University in Canada, analyzed data on 568 young people, aged between four and 22, diagnosed with ADHD. Other factors, including sex and socioeconomic status, were also looked at.

As well as IQ levels making a difference, the research showed a higher socioeconomic status and non-White maternal ethnicity tended to mean ADHD was diagnosed later than it could have been. How the ADHD behavior was shown externally made a difference too – in people who internalize symptoms, for example, diagnosis is later on average.

"We first found that higher IQ predicted later ADHD age of diagnosis," write the researchers in their published paper. "Second, we found that hyperactive-impulsive symptoms and externalizing symptoms were related to earlier diagnosis in both boys and girls."

People with ADHD exhibit differences in the way they move, concentrate, and control their impulses. The condition can have a significant impact on learning and development in children, which is why the earlier a diagnosis is made, the better.

A late diagnosis, or no diagnosis at all, can lead to behavioral problems and below-par academic performance. While previous studies have suggested there's often a later diagnosis for both girls and those with a higher IQ, here the researchers wanted to look at both factors together.

While the researchers were expecting the impact of IQ on diagnosis age to be more noticeable in girls, based on that earlier research, this wasn't borne out by the data – both girls and boys were affected more or less in the same way.

"Future studies should include individuals who are not diagnosed, because it may lead to the inclusion of girls whose diagnoses have been missed because of factors described in this study," write the researchers.

The findings give health professionals and parents some useful pointers when it comes to recognizing ADHD: that kids who come across as smarter, or who are better able to hide their symptoms, are more likely to get overlooked.

We know that ADHD presents itself in many different forms, and some of the more subtle signs and symptoms may be getting missed, the researchers suggest – especially in kids who appear to be academically gifted.

To make the picture even more complicated, ADHD is often misdiagnosed as something else. Trying to pin down what is ADHD and what isn't can be challenging, but studies such as this one are helping.

"Clinicians should be mindful of these individual differences and demographic factors, and these should be considered when giving diagnoses," write the researchers. "On the other hand, these factors may be inhibiting individuals from seeking a diagnosis."

The research has been published in the British Journal of Clinical Psychology.