Relative Age and ADHD Diagnosis and Treatment

William N. Evans, University of Maryland
Melinda Sandler Morrill, North Carolina State University
Steve Parente, University of Minnesota

According to the National Institute of Mental Health, when evaluating whether a child has ADHD, health professionals should consider whether the behaviors “happen more often in this child compared with the child’s peers.” 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, 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. 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 relative age to peers in class, and the resulting relative behavior, leads some children who are comparatively immature to receive medically inappropriate stimulant prescription medication.