How common is attention-deficit/hyperactivity disorder? Incidence in a population-based birth cohort in Rochester, Minn.

CONTEXT The frequency of occurrence of attention-deficit/hyperactivity disorder (AD/HD) is in dispute. This uncertainty has contributed to the concern that too many children in the United States are being treated with stimulant medication. OBJECTIVES To determine the cumulative incidence of AD/HD in a population-based birth cohort and to estimate the prevalence of pharmacologic treatment for children who fulfill research criteria for AD/HD. DESIGN Population-based birth cohort study. SETTING AND SUBJECTS All children born between 1976 and 1982 in Rochester, Minn, who remained in the community after age 5 years (N = 5718). MAIN OUTCOME MEASURES Medical and school records were reviewed for clinical diagnoses of AD/HD and supporting documentation (symptoms consistent with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria and positive results for AD/HD-related questionnaires). Research-identified cases were defined as: (1) "definite" AD/HD (clinical diagnosis and at least one type of supporting documentation); (2) "probable" AD/HD (clinical diagnosis but no supporting documentation or no clinical diagnosis but both types of supporting documentation); (3) "questionable" AD/HD (no clinical diagnosis, but at least one type of supporting documentation); and (4) "not AD/HD" (all other subjects). Information about pharmacologic treatment for AD/HD was abstracted for all subjects. RESULTS The highest estimate of the cumulative incidence at age 19 years (with 95% confidence interval) of AD/HD (definite plus probable plus questionable AD/HD) was 16.0% (14.7-17.3). The lowest estimate (definite AD/HD only) was 7.4% (6.5-8.4). Prevalence of treatment with stimulant medication was 86.5% for definite AD/HD, 40.0% for probable AD/HD, 6.6% for questionable AD/HD, and 0.2% for not AD/HD. CONCLUSIONS These results provide insight into the apparent discrepancies in estimates of the occurrence of AD/HD, with less stringent criteria resulting in higher cumulative incidence. Children who met the most stringent criteria for AD/HD were most likely to receive pharmacologic treatment.