"Our study findings suggest that there may be a large number of factors that affect ADHD diagnosis rates, including cultural factors that may influence the treatment-seeking behavior of some groups," said study lead author Darios Getahun, MD, PhD, from Kaiser Permanente Southern California's Department of Research & Evaluation. "These findings are particularly solid given that our study relied on clinical diagnoses of ADHD based on the criteria specified within the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders and that it represents a large and ethnically diverse population that can be generalized to other populations."In addition, the study found that boys were three times more likely to be diagnosed with ADHD than girls. Higher family incomes also were associated with the likelihood of ADHD diagnosis; children from families with a household income of more than $30,000 a year were nearly 20 percent more likely to be diagnosed with ADHD than children from families making less $30,000. According to the Centers for Disease Control and Prevention, ADHD is one of the most common neurobehavioral disorders of childhood. The CDC estimates that between 4 percent and 12 percent of school-aged children have the disorder, which generates health care costs of between $36 billion and $52 billion per year. Children with ADHD are more likely to experience learning problems, miss school, become injured and experience troublesome relationships with family members and peers, according to the researchers. "While the reasons for increasing ADHD rates are not well understood, contributing factors may include heightened awareness of ADHD among parents and physicians, which could have led to increased screening and treatment," said Dr. Getahun. "This variability may indicate the need for different allocation of resources for ADHD prevention programs, and may point to new risk factors or inequalities in care."