Study: Minimum ADHD Incidence Is 7.5 Percent
Educators on the front lines of spotting and helping students with attention deficit hyperactivity disorder may lack a clear picture of the syndrome's prevalence, but a new study aims to help clarify the question.
In recent years, researchers have estimated that anywhere from 1 percent to 20 percent of school-age children in the United States have ADHD. Confusion over the rate of cases has fanned concerns that children are overidentified as having the disorder, or are overmedicated to treat it.
But a study released this month attempts to provide a clearer view of the rate of ADHD cases. In an analysis of the syndrome's prevalence in one Minnesota school district, researchers at the Mayo Clinic in Rochester, Minn., found that ADHD affected a minimum of 7.5 percent of school-age children. Because the study focused on one district, however, the researchers caution that the rates of ADHD could vary in areas with different demographics.
"We took a hard look at this condition from a number of angles to help pinpoint the occurrence rates," said Dr. William J. Barbaresi, a Mayo Clinic specialist in developmental and behavioral pediatrics and the lead author of the study. "The results from this study provide much-needed baseline information for comparison with populations in other communities."
Variety of Criteria
The Mayo Clinic researchers looked at 8,548 children born between Jan. 1, 1976, and Dec. 31, 1982, to mothers who lived in the townships that make up the Minnesota Independent School District in Olmsted County, Minn. Using different sets of research criteria, the researchers identified cases of ADHD as being definite, probable, or questionable. Using those varying criteria made the study different from previous ones, the researchers say.
The resulting estimates, which vary greatly depending on the strictness of the criteria, could help explain why past studies have arrived at so many different rates, the authors say. Some studies of the incidence of ADHD, they say, relied on single sources of information to establish the diagnosis, such as teacher questionnaires or diagnostic interviews.
When using the strictest research criteria, which included a clinical diagnosis and supporting documentation from medical and school records, the researchers concluded that 7.5 percent of school-age children in the district definitely had ADHD. Summing the cases of definite and probable ADHD gave them a figure of 9.6 percent. Counting all the definite, probable, and questionable cases led the researchers to arrive at an estimate of 16 percent.
A child with the disorder may have trouble paying attention, staying on task, and controlling impulses, such as inappropriately calling out in class. In many cases, stimulant medicines such as methylphenidate, often sold under the brand name Ritalin, are used to treat the disorder.
The Mayo Clinic report is featured in the March issue of the Archives of Pediatrics and Adolescent Medicine. In a related editorial in that issue, Dr. Esther H. Wender, a Chappaqua, N.Y.-based physician and ADHD expert, writes that she believes the rate of ADHD will never truly be known because diagnosis is based on the subjective judgment of doctors.
"The published diagnostic criteria lend an aura of objectivity to the diagnosis, but the application of these criteria is based on subjective judgments regarding the accuracy of information given by parents and teachers," Dr. Wender writes. "Only when and if biological markers can be found to identify the condition will this subjectivity be eliminated."
Vol. 21, Issue 28, Page 10