Most research supports the theory that ADHD is a physiological condition and is therefore present at birth. However, the noticeable beginning of ADHD symptoms typically occurs early in childhood. Before the age of 5, ADHD symptoms may be difficult to diagnose, because most young children are highly energetic, easily distractible, and impulsive. Therefore, the average age of diagnosis is 8 years for ADHD and 10 years for ADD. The difference in diagnosis age likely occurs because hyperactive symptoms tend to draw more attention as a result of the child's active, noisy behavior than do pure attention problems that are calm and quiet. Observers can hardly help but notice wild and out of control behavior, while they may have to carefully study a child to see the distracted and inattentive behaviors. Often, as children grow older, their ADHD symptoms decrease in severity. 30% to 70% of children with ADHD continue to experience symptoms into adulthood, though they may be less pronounced than they were during childhood.
By 1996, at least 40% of children referred to outpatient child psychiatry providers were diagnosed with ADHD. According to the Centers for Disease Control, 4.4 million youth between the ages of 4-17 have been diagnosed with Attention-Deficit/Hyperactivity Disorder. The DSM IV-TR suggests that the prevalence rate of ADHD in children is 3% to 7%, and 2% to 5% in adults. Using these prevalence rates it can be estimated that in a classroom of 25 to 30 children, at least one of those children will have ADHD.
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As of 2003, approximately 2.5 million young people were being treated with medication for ADHD symptoms. Prescription medication rates for ADHD are increasing in usage dramatically in the United States, with certain geographical areas tripling or quadrupling the number of prescriptions written ten years ago. Although increasing medication rates may be related to improved awareness and diagnosis, some professionals have different theories. Some researchers speculate that increasing ADHD prevalence and treatment rates may be related to changes associated with living in the digital age, such as decreased levels of physical activity and less exposure to the natural environment, which is thought to lead to increased amounts of restless and impulsive behavior (we will discuss this idea further in our section on causes of ADHD).
Boys are diagnosed with ADHD three times more often than girls; and adult males are diagnosed more often than adult females. Males of all ages tend to display, by far, more hyperactivity than females and slightly more symptoms of inattention than women. Approximately 10% of all males and 4% of females have been diagnosed with ADHD.
The difference in prevalence rates between males and females is an interesting phenomenon. Not only do boys tend to be more often hyperactive, but boys who are inattentive often play around (and get in trouble). In contrast, girls who are inattentive tend to daydream. These tendencies may at least partly explain why more males are diagnosed than females. However, it is not really clear whether there is a true gender-based difference in genetic susceptibility to ADHD, or if females are simply much less likely to be diagnosed than men. Research is being conducted to try to determine the source of these differences.
Although ADHD is more frequently diagnosed in the United States, it has been found in every country that has been studied. Prevalence rates range from 1.7-10% in Canada, Germany, the Netherlands, New Zealand, Norway, Puerto Rico, and the United Kingdom. Interestingly, the rates of diagnosis are rising in industrialized countries. These increasing rates may be explained in part by an enhanced awareness of the disorder in other countries, resulting in improved diagnosis and treatment.