At a young and impressionable age, children can forget to do their chores, sporadically daydream in school, or even have trouble sitting still. These behaviors, if done occasionally, are relatively normal for children. But once these behaviors become habitual at school and home, then this is likely a sign of a common childhood disorder called attention-deficit hyperactivity disorder (ADHD). According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), an estimated three to seven percent of school-aged children have ADHD, with a total of 5.4 million children in the U.S. with an ADHD diagnosis.

The rates of ADHD diagnosis in the U.S. have steadily increased by an average of 5.5 percent from 2003 to 2007, and are expected to increase over the next few years as more parents are found to report the disorder in their children. In the UK, children were found to be less likely to be diagnosed with ADHD than U.S. children, according to a new study. The study found that autism rates, however, are increasing in the UK.

Findings published in the Journal of Autism Developmental Disorders suggest it is important to identify the diagnostic trends and the reasons behind them to explain the rise in ADHD diagnosis in American children compared to British children, and why autism diagnosis is on the rise in the UK. In a 2009 study in the U.S., 6.3 percent of children between the ages of five and nine were diagnosed with ADHD, compared to just 1.5 percent of parents in the UK who reported a ADHD diagnosis in their children between the ages of six and eight.

The team of researchers looked at data from the UK Millennium Cohort Study that included a sample of more than 19,000 children as a representation of the UK population. "Our findings reveal that doctors in the UK are far less likely to deploy the ADHD label than their US counterparts,” said Dr. Ginny Russell of the University of Exeter Medical School and lead author of the study. The researchers believe cultural factors, such as different criteria for diagnosing ADHD or parental concerns over drug treatment for this disorder, could influence the amount of reported cases in both countries.

Children who are diagnosed with ADHD in the U.S. are more likely to be diagnosed with conduct disorder in the UK, according to an article published in World Psychiatry, the official journal of the World Psychiatric Association. Kids who are categorized as suffering from conduct disorder tend to have behavioral and emotional disturbances, such as aggression toward people and animals.

Currently, ADHD affects approximately five in 100 school-aged children in the UK between the ages of three and seven, says Parents are advised that it is normal for children under the age of five to be inattentive and restless, in order to avoid overdiagnosis due to parental concerns. Russell believes it is equally as important to not underdiagnose. "Various criteria in different cultural contexts may mean that children are missing out on health services -- the diagnostic label may determine the support families receive,” he said.

The same study led by Russell suggests that while ADHD diagnosis is less likely in UK children than in U.S. children, autism diagnosis is continuously rising in the UK. The researchers found that some 1.7 percent of UK parents reported that their children (between the ages of six and eight) had been diagnosed with having autism spectrum disorder (ASD). Russell and his team speculate that the increased awareness of autism and its destigmatization may possibly contribute to the rise in diagnoses, reports Science Daily.

But do these increased rates of autism diagnoses reflect real rises in the occurrence of the disorder or are they due to a change in diagnostic criteria and increased awareness? To address this question, Russell is observing two UK birth cohort studies. "It is important to establish if there is a real increase in children with symptoms because we can then try to discover the environmental or social factors behind the rise in order to take preventive measures," he said.

To read more about autism and its symptoms, visit Autism Speaks.