Researchers from North Carolina State University looked at the rates of ADHD diagnosis and treatment in children from 1996 to 2006 and found large discrepancies based on their dates of birth. They found that children born just after the cut-off date for their academic year group were 25 per cent less likely to be diagnosed as having ADHD than children born just before the cutoff.
The report says, 'The relative immaturity of these young-for-grade children may be mistaken as ADHD, due to the nature of the diagnostic guidelines that suggest a comparison with a child's peers ... ADHD is an underlying neurological condition and incidence rates should not change dramatically from one birth date to the next.'
The report says children with ADHD are more likely to have learning difficulties and to achieve lower test scores, and that outside of the classroom they are more likely to use illegal drugs, be involved in car accidents and suffer from other psychiatric conditions.
It is estimated that five in 100 school-aged children in Britain have ADHD, according to figures published by the National Institute for Health and Clinical Excellence (NICE).
Dr Melinda Morrill of North Carolina State University, co-author of the study, said, 'We believe that younger children may be mistakenly diagnosed as having ADHD when in fact, they are simply less mature.
'We are not downplaying the existence or significance of ADHD in children. What our research shows is that similar students have significantly different diagnosis rates depending on when their birthday falls in relation to the school year.'
Tim Oates, director of assessment, research and development at Cambridge Assessment, said, 'This is consistent with our own international literature study which looked at the rate of diagnosis in England of summer-born children with SEN. The research showed that the rate of SEN in summer-born children is unexpectedly high.'
'Measuring inappropriate medical diagnosis and treatment in survey data: The case of ADHD among school-age children' is published in the Journal of Health Economics.