Study estimates global prevalence of ADHD

Attention-deficit/hyperactivity disorder (ADHD) affects 7.2% of children worldwide, a new meta-analysis estimates. The review provides a benchmark pooled prevalence estimate against which to assess whether ADHD might be under- or overdiagnosed in various populations, its authors say.

Researchers analyzed 175 studies that included 179 prevalence estimates in 1,023,071 children over 36 years and found an overall pooled estimate of 7.2% (range, 6.7% -7.8%) “by systematically extracting the most robust and conservative estimates” from the studies. 

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The studies were widely distributed geographically, although the highest percentage (31%) were done in Europe. Most (74%) examined school populations; only 10% employed a whole-population approach with random selection. Most were from single towns or regions, which limited their generalizability, the researchers acknowledge.

The use of clinician informants in the studies declined over time while the use of parent informants increased. Interviews gave way to reliance on symptom-only checklists, and use of full diagnostic criteria from the Diagnostic and Statistical Manual of Mental Disorders (DSM) decreased compared with partial criteria. Most studies (75%) had a moderate or low risk of bias, but only 17% had a low risk.

In addition to establishing an overall pooled benchmark prevalence figure for ADHD, the researchers explored whether prevalence estimates have increased over time with use of evolving diagnostic criteria in different editions of the DSM.

Although they’d expected to find marked increases between the DSM third edition (DSM-III), revised third edition (DSM-III-R), and fourth edition (DSM-IV), they found no statistically significant differences in pooled estimates. In multivariable analyses, however, studies that used the DSM-III-R criteria showed lower prevalence estimates than the DSM-III or DSM-IV.

Region was the only other study characteristic that affected variations in prevalence estimates in multivariable analyses. Estimates were lower for studies conducted in Europe than North America and higher for the Middle East than North America.

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Citing significant concern among professionals and the general public about possible overdiagnosis of ADHD, the researchers maintain that their prevalence estimates provide a suitable benchmark for determining whether overdiagnosis (or underdiagnosis) has occurred because “over time and editions of the DSM, the high-quality estimates of prevalence [in their meta-analysis] are relatively consistent.”

The researchers conclude that in light of the range of ADHD prevalence estimates in published studies and the fact that the estimates are important to both professionals and the lay public, the DSM diagnostic criteria must be applied systematically and in a standard manner.