How common is ADHD, really?
Answering that question is surprisingly difficult. It depends on what group of people you consider and how you diagnose ADHD.
Perhaps no surprise, then, that different studies have tended to come up with different numbers.
But a new meta-analysis, or study of studies, looks across the evidence available to come up with a single estimate for the global prevalence of adult ADHD.
To do so, researchers based in China and the UK searched for studies on the prevalence of ADHD done between 2000 and 2019. They selected studies done on adults from the general population. In other words, they did not include studies done on specific groups that might be less representative of the wider population (for example, people in psychiatric hospitals, where you’d expect to find a high rate of ADHD).
Then they considered studies that diagnosed ADHD using two contrasting methods. In studies diagnosing persistent ADHD, people only qualified for ADHD if they currently met the threshold for ADHD symptoms and reported having ADHD symptoms since childhood. Studies diagnosing symptomatic ADHD, however, categorized people based on whether they had ADHD symptoms at the time of the study without asking about childhood.
Generally, studies gave lower estimates of ADHD prevalence when they diagnosed persistent ADHD due to the more stringent diagnostic criteria than symptomatic ADHD. Of the previous studies the researchers found, 20 looked at symptomatic ADHD, 19 looked at persistent ADHD, and one looked at both.
Analyzing data across those studies, the researchers arrived at estimates of a global rate of 2.58 percent for persistent ADHD and 6.76 percent for symptomatic ADHD.
That translates into about 140 million people internationally with persistent ADHD, or 366 million with symptomatic ADHD.
One takeaway that emerges from those results is the need for better methods of diagnosing ADHD. Although diagnostic tests can be a helpful indicator of ADHD symptoms, the estimate for the global rate of ADHD varied substantially based on which diagnostic method was used – and it varied even more between individual studies.
Still, three and seven percent are in the same approximate ballpark: both figures suggest that while fewer than one in ten adults may qualify for an ADHD diagnosis, tens or hundreds of millions of people around the world live with ADHD.
While some uncertainty remains about the exact global incidence of ADHD, then, it seems clear that ADHD is a public health issue with a wide-reaching impact around the world.