August 18th, 2010
A new study provides perspective on the diagnosis of ADHD among children. Using a clever research design, researchers demonstrate that those who were younger when they started kindergarten are considerably more likely to receive an ADHD diagnosis, and to be put on stimulants, than are those who were older when starting school.The study provides additional evidence that at least a significant fraction of ADHD diagnoses represent a mismatch between the child’s personal characteristics and the demands of most contemporary schools.
The study, as described in the abstract, makes the assumption that there is a “real” ADHD, which “is an underlying neurological problem,” they have to assume that what we are seeing in their data is “misdiagnosis.” However, the situation is likely more fluid with some children having a range of neurological conditions which lead them to be mismatched to the school environment. Some of these children likely will have difficulties in many contemporary environments. Others, however, are just not ready, or not suited, to schools as currently organized. It is a mistake to assume that there is a clear ADHD condition that only requires correct diagnosis. As long as the diagnosis is based on behavior, there are likely to be many factors — neurological, personal temperament and history, familial, and larger environmental — contributing to a child receiving the diagnosis. For many, at least, the diagnosis will represent a mismatch between personal characteristics and environmental demands.
Here is the study abstract:
We exploit the discontinuity in age when children start kindergarten generated by state eligibility laws to examine whether relative age is a significant determinant of ADHD diagnosis and treatment. Using a regression discontinuity model and exact dates of birth, we find that children born just after the cutoff, who are relatively old-for-grade, have a significantly lower incidence of ADHD diagnosis and treatment compared with similar children born just before the cutoff date, who are relatively young-for-grade. 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.
And here is a MedPage Today article giving further details on the study:
ADHD Diagnosis Rate May Vary by Age at School Entry
By Todd Neale
The timing of a child’s entry into kindergarten may influence the chances of receiving a diagnosis of attention-deficit/hyperactivity disorder (ADHD), which suggests that some diagnoses are inappropriate, researchers found.Children born just before the entry cutoff date — and thus young for their grade — had higher rates of diagnosis and treatment with stimulants than those born just after the cutoff, according to William Evans, PhD, an economist at the University of Notre Dame, in South Bend, Ind., and colleagues.
The fact that the birthdays of the two groups of children were close together suggests that biological differences most likely could not explain the disparities in diagnosis and treatment, the researchers noted in their paper, which was published online in the Journal of Health Economics.
“If one assumes that the true incidence rate of ADHD is uniform over a small window around the age at school start cutoff, the estimates provide compelling evidence that a large fraction of ADHD diagnoses are not the result of an underlying medical condition,” they wrote.
Rather, they speculated, it could be that children who are young relative to most of their classmates may simply act in a more immature manner. This behavior may increase the likelihood of being diagnosed with ADHD, because comparisons with peers may be used in diagnosis.
“These results suggest that the comparison sample for diagnosis should not be other children in class but rather, other children of a similar age within a class,” Evans and his colleagues wrote.
The recent rise in the rate of ADHD has raised concerns of overdiagnosis, according to the researchers.
To examine whether relative age at school entry influences the chances of being diagnosed with the condition, Evans and his colleagues formed statistical models from three data sets.
They pulled data on diagnosis from the 1997 to 2006 National Health Interview Survey, and data on prescription stimulant use from the 1996 to 2006 Medical Expenditure Panel Survey and a private insurance prescription drug claims database for 2003 to 2006.
The analyses were restricted to children living in states with strict kindergarten eligibility cutoff dates, and those with birthdays within 120 days of those dates.
In all three data sets, children who were born before the cutoff date — and who would be younger than the majority of their classmates — were more likely to be diagnosed with or treated for ADHD than those who were born after the cutoff date and would have been a year older before entering school.
In the NHIS, nearly one in every 10 children who were young for their grade (9.7%) received an ADHD diagnosis, compared with 7.6% of the older children.
In the MEPS, stimulant use was higher in the children who were relatively younger (4.5% versus 4%). A similar drop after the cutoff date was seen in the private insurance claims database (6.5% versus 5.2%).
“To put our estimates into perspective, an excess of 2 percentage points implies that approximately 1.1 million children received an inappropriate diagnosis and over 800,000 received stimulant medication due only to relative maturity,” the researchers wrote in their paper.
The same pattern was not observed for other common childhood diseases and prescription medications.
A forthcoming study by a different group of researchers also found an increased likelihood of ADHD diagnosis in children who were young for their grade, according to Evans and his colleagues.
“The robustness nature of the results across samples in this paper and the [other study] is encouraging and suggests that the results presented … are not spurious but represent true misdiagnosis of ADHD,” they wrote.