NEW YORK (Reuters Health) - The wide range in estimates of the prevalence of attention-deficit/hyperactivity disorder (ADHD) are largely due to variations in the stringency of criteria used to diagnose this condition, US researchers report.

In the largest study of its kind to date, Dr. William J. Barbaresi and colleagues from the Mayo Clinic in Rochester, Minnesota, found that by 19 years of age, 7.4% of children in their study met the strictest criteria for a diagnosis of ADHD. These children were also the most likely to receive stimulant medications for treating the condition.

"The frequency of occurrence of ADHD is in dispute, with reported prevalence varying from 1% to 20% among school-aged children," the researchers report in the March issue of the Archives of Pediatrics and Adolescent Medicine. "This uncertainty has contributed to the concern that too many children in the US are being treated with stimulant medication."

To investigate how common ADHD really is, the researchers evaluated medical and school records for 5,718 children, representing all of the children born in Rochester between 1976 and 1982 who still lived there after age 5.

In all, 1,344 of the children were identified as possibly having ADHD. The investigators then placed these children in categories based on their ADHD status, which included a "definite" diagnosis, "probable" diagnosis, "questionable" diagnosis, or "not ADHD."

The highest estimate for cumulative ADHD prevalence by age 19, including all children categorized as having a definite, probable or questionable diagnosis of ADHD, was 16%, the team found.

Broken down further, 9.4% of children were categorized as having definite or probable ADHD by age 19, while 7.4% definitely had ADHD.

Barbaresi's team found that the children who met the most stringent requirements for an ADHD diagnosis were most likely to be receiving treatment with stimulant medication. Among children with a definite ADHD diagnosis, 86.5% were taking such medication. Forty percent of children with a probable diagnosis of ADHD were taking stimulants, while 6.6% with a "questionable" ADHD diagnosis were on the drugs. And among kids who did not have ADHD, 0.2% were on the medications.

"We believe that the cumulative incidence of 7.5% for definite ADHD is the most accurate estimate of the occurrence of this disorder," Barbaresi and colleagues write. "Our criteria for definite ADHD are similar to those specified in the recent American Academy of Pediatrics practice guidelines for ADHD."

The authors conclude that "the use of three different case-identification criteria helps explain the wide variation in the reported frequency of occurrence of ADHD in the existing literature."

SOURCE: Archives of Pediatrics and Adolescent Medicine 2002;156:217-224.

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