Attention Deficit-Hyperactivity Disorder and Month of School Enrollment.
Level 3 - non-randomized controlled study
Non-randomized, quasi-experimental retrospective cohort study using administrative claims data.
PubMed 30485780 · doi:10.1056/NEJMoa1806828
What was done
Using a large U.S. insurance claims database from 2007 through 2015, researchers conducted a retrospective cohort study of 407,846 children born between 2007 and 2009. They compared rates of claims-based ADHD diagnosis (ICD-9 codes) and ADHD medication treatment between children born in August (the youngest in a cohort) and September (the oldest in a cohort) across states with and without a mandatory September 1 age cutoff for kindergarten enrollment. Additional comparisons evaluated other birth months and control health conditions (asthma, diabetes, obesity).
What was found
In states with a September 1 school entry cutoff: - August-born children had a significantly higher ADHD diagnosis rate than September-born children: 85.1 per 10,000 (309 cases among 36,319; 95% CI, 75.6 to 94.2) vs. 63.6 per 10,000 (225 cases among 35,353; 95% CI, 55.4 to 71.9), an absolute difference of 21.5 per 10,000 (95% CI, 8.8 to 34.0). - In states without the September 1 cutoff, the difference was not statistically significant: 8.9 per 10,000 (95% CI, -14.9 to 20.8). - ADHD treatment rates were higher for August-born children (52.9 per 10,000; 95% CI, 45.4 to 60.3) than September-born children (40.4 per 10,000; 95% CI, 33.8 to 47.1), an absolute difference of 12.5 per 10,000 (95% CI, 2.43 to 22.4). - No significant differences were observed for other month pairs, in states with non-September cutoffs, or for asthma, diabetes, or obesity.
Why it matters
Relative age within a school grade influences ADHD diagnosis and medical treatment, suggesting that behavioral immaturity due to younger age may be misattributed to ADHD.
Limits
The study relied entirely on commercial insurance diagnostic codes and prescription claims, lacking clinical chart confirmation, symptom severity metrics, or classroom behavioral observations. Actual school entry dates and grade retention or acceleration were inferred rather than directly tracked.
Cited by
- partial Boys born in July and August are three times more likely to be diagnosed with ADHD than boys born in other months.