The study is based on data of 8 to 15 years olds gathered between 2001 and 2004 from the National Health and Nutrition Examination Survey (NHANES) from the National Center for Health Statistics at the Centers for Disease Control and Prevention. NHANES is a nationally representative sample of the United State population, designed to collect information about the health and diet of people in the U.S.

Prenatal tobacco exposure was measured by maternal reports of cigarette use during pregnancy. Lead exposure was assessed using current blood lead level. Some 8.7 percent of the 3,907 children in the study met diagnostic criteria for ADHD. The diagnosis for ADHD was based on the Diagnostic and Statistical Manual for Mental Disorders, Fourth Edition, considered the "gold standard" for defining specific mental health conditions.

Source: Cincinnati Children's Hospital Medical Center