Attention-deficit/hyperactivity disorder (ADHD) is a neurobehavioral disorder of childhood that is difficult to diagnose and has no known cause. There is some concern that diagnoses for ADHD are not for underlying behavioral problems but rather represent age-appropriate differences in behavior. This project seeks to determine whether a child that is “young for their grade” and is hence relatively immature, is more likely to have been diagnosed with ADHD.
The research exploits the sharp discontinuity in school enrollment generated by kindergarten eligibility laws, which are determined at the state level. Children born just before the cutoff s will, on average, be young for their age; while children born just after the cutoff must, on average, wait a year to enter school and therefore will be the oldest children in their class. ADHD is an underlying neurological problem where incidence rates should not change dramatically from one birth date to the next. If diagnosis rates do shift appreciably based on small changes in birth dates, then the diagnosis is not based on underlying conditions but rather behavior relative to peers in class. This project uses data from the National Center for Health Statistics from 1985 through 2004 to demonstrate the relationship between eligibility date and grade for age. These data are used to test whether children born just prior to the kindergarten eligibility cut-off date have higher rates of ADHD diagnosis than children born just after those dates.