Nearly 1 million ADHD misdiagnoses, study says

CNN recently reported that many psychologists are seeing a lot of misdiagnoses of ADHD. Readers had a lot to say about that.

Now studies are backing up anecdotal evidence that ADHD gets inappropriately applied to many children.

An analysis by economist Todd Elder at Michigan State University suggests that about 900,000 children who have been told they have ADHD in America may not have the condition at all. The study will appear in the Journal of Health Economics.

Elder found that how old a child is relative to peers in the same class also affects teacher perception of ADHD symptoms. In other words, teachers tended to perceive ADHD symptoms more in younger kids than older kids, even in the same grade. Younger children were also more likely to take stimulant medication for ADHD. The study authors suggest that children who are young for their grade may get an inappropriate diagnosis because teachers mistake their immaturity for ADHD.

The age at which a child starts school influences teachers' perceptions of whether the child has ADHD-related symptoms, but does not as strongly affect the parents' perceptions, the study said. Data for this research came from the Early Childhood Longitudinal Study Kindergarten Cohort.

Another study in the Journal of Health Economics, led by William Evans at the University of Notre Dame, found similar results regarding the age of the child and the likelihood of ADHD diagnosis. Researchers looked at data from the National Health Interview Survey, the Medical Expenditure Panel Survey, and a nationwide private insurance company.

Both Elder's and Evans' studies found that being young in a grade more than doubles the likelihood of receiving an ADHD diagnosis or treatment. Evans' study says:

Since ADHD is an underlying neurological problem where incidence rates should not change dramatically from one birth date to the next, these results suggest that age relative to peers in class, and the resulting differences in behavior, directly affects a child’s probability of being diagnosed with and treated for ADHD.

The cost of a misdiagnosis on the health and well-being of a child is tremendous, Elder writes. Chronic stimulant medication for ADHD may lead to possible cardiovascular problems and a reduction of children's growth rates, studies have found. These medications also take a substantial toll on the family. Elder estimates that $320 million to $500 million is annually spent on ADHD treatments for children who inappropriately received the diagnosis.