5 Best of 2019: Most-Read Pediatrics Viewpoints

William T. Basco, Jr, MD, MS


January 21, 2020

#4: Can a Month Make a Difference in ADHD?

Rising rates of attention-deficit/hyperactivity disorder (ADHD) diagnoses have led to concerns about potential overdiagnosis. As recently as 2016, it was calculated that 1 in 20 US kids were taking medication for the condition.

Could the month in which a child is born contribute to the likelihood of one day receiving an ADHD diagnosis? An analysis of data from 400,000 children included in a health insurance claims database concluded that the answer is yes.

The investigators found that children with birthdays in August of any given year had an ADHD diagnosis rate that was fully one third greater than that of children of similar age, gender, ethnicity, and socioeconomic status who were born in September (85.1 per 10,000 children vs 63.6 per 10,000 children). And August-born children were more likely to be medicated than their peers born just a month later. No differences in the diagnosis of other chronic conditions, such as asthma, obesity, or diabetes, based on month of birth were found. These differences were also not observed for other month-to-month comparisons.

The reason? The August children were more likely to start school around their fifth birthday, whereas their September peers often did not enroll until a year later, owing to birthdate cutoffs established by the school system. Thus, September-born children were more likely to reach age 6 around the time they enrolled in kindergarten.


Anyone who has read Malcolm Gladwell's book Outliers: The Story of Success would not be surprised by these findings. Very similar results were found in another study of over 1 million children in the United Kingdom, where children who were in the youngest quartile of their class had a greater likelihood of being diagnosed with ADHD than kids in the oldest and second-oldest quartiles.

These data suggest that we should in some way account for the age of a child before making a new ADHD diagnosis. That is not to discount the potential for true ADHD in a younger child or the need for treatment. Although population-based data such as these can't necessarily be applied to the care of any individual child, age relative to peers is one factor we should consider when making diagnosis and treatment decisions.


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