ADHD is a persistent pattern of inattention and/or hyperactivity that interferes with functioning or development. ADHD begins in childhood, but persists into adulthood in up to 65% of cases. Population surveys suggest that ADHD occurs in most cultures in about 5% of children and 2.5% of adults. Despite criticisms of over diagnosis, in the USA, the National Comorbidity Survey Replication estimates that as many as 75% of people with ADHD have never been diagnosed, and 90% remain untreated.