ADHD Incidence in Children: Trends, Statistics & Diagnosis

Introduction: Defining the Problem

Attention Deficit Hyperactivity Disorder (ADHD), a neurological condition characterized by inattention, restlessness, and impulsivity, is commonly diagnosed in early childhood and affects between 3% and 5% of American children, according to the National Institute of Mental Health. "In a classroom of 25 to 30 children, it is likely that at least one of them will have ADHD" (Ramer, p. 4). Studies conducted in this area, and many school teachers, suggest these numbers are conservative estimates. There is a growing belief that ADHD is increasing in incidence. The thesis of this paper is that Attention Deficit Hyperactivity Disorder (ADHD) has increased in incidence during a ten-year span for school-aged children.

Public perception often holds that the incidence of ADHD is rising, but it is unclear whether this is actually the case. Research on the incidence of ADHD among children has been inconclusive, with studies suggesting a range of incidence from 1% to 18%. This variation exists because there is no standardized research protocol for reporting ADHD, making it difficult to determine whether incidence is genuinely increasing (Barkley, 2006).

If ADHD becomes evident during the preschool or elementary years and the median age of onset is seven years, the disorder may still be diagnosed later, at which point the child may have had it for several years (Kessler, p. 617). According to 2001 figures from the American Society of Pediatrics, 12% of youth in America suffer from the disorder. It is the most commonly diagnosed behavioral disorder among children, but misunderstanding of its symptoms and etiology has created confusion and controversy. This misunderstanding has led to undertreatment in children (Dopheide, p. 1).

Current Status of ADHD in the United States

In November 1998, the National Institutes of Health (NIH) invited 44 experts from across the United States — in psychiatry, psychology, epidemiology, biostatistics, and pediatrics — to develop a consensus statement addressing key diagnostic and treatment issues related to ADHD (NIH, p. 1). The resulting statement confirmed that ADHD is a valid disorder with measurable and significant impairment in functioning caused by inattention, impulsivity, and hyperactivity. These experts reported a 3% to 5% incidence in school-aged children and called for improved diagnosis, treatment, and follow-up. They strongly encouraged greater cooperation between parents, teachers, and healthcare providers to achieve optimal assessment and treatment. The most effective treatments for relieving symptoms, according to the research, were stimulants, though there was no consensus on the threshold of symptoms most appropriate for stimulant therapy (NIH, p. 5).

A well-documented public health concern is the underdiagnosis and suboptimal treatment of children with ADHD. One study found that only 50% of children with identified ADHD in practice settings actually receive care that meets the guidelines of the American Academy of Child and Adolescent Psychiatry. A lack of pediatric specialists, insurance obstacles, and long waiting lists are barriers to providing appropriate services.

In only seven years — between 1989 and 1996 — services such as health counseling for children with ADHD increased ten-fold, and diagnostic services increased three-fold. Psychotherapy provision, however, decreased from 40% to 25% during the same period. Follow-up care also decreased, from 90% to only 75%. Additional barriers to appropriate diagnosis and treatment included fear of stigma, uncertainty about the long-term effects of treatment, and fear of substance abuse (Hoagwood, p. 198).

One epidemiological study tracked 220,000 very young children through Medicaid and HMO databases from 1991 to 1995 and found that 1.2% of these preschoolers were prescribed stimulants, 1.1% were prescribed antidepressants, and 0.32% were prescribed clonidine for behavioral control. One way of tracking the prevalence of ADHD is through prescription of the drugs used to treat it. This study shows a three-fold increase in stimulant prescribing, a two-fold increase in antidepressant prescribing, and a 28-fold increase in clonidine prescribing between 1991 and 1995. A greater acceptance of pharmacological treatments for behavioral disorders in children was cited as a major reason for the increased prescribing rates for 2- to 19-year-olds (Zito, p. 1026).

Jeanette Ramer, associate professor of pediatrics, believes there has been an increase in ADHD. It remains uncertain whether the rise in numbers is due to more children being born with the condition or due to increased recognition and more frequent diagnosis. Ramer believes it is both. She also believes the disorder is genetic: "About half the time when we diagnose a child, a parent will also have it" (Ramer, para. 2).

Regional and Demographic Variability

Although rates for the incidence of ADHD are 5 to 10 times greater in the United States compared to other countries, there is also significant regional variability in the diagnosis and treatment of ADHD within the country. For example, in one Virginia school system, 8% to 10% of 30,000 children in second through fifth grade were diagnosed with ADHD, compared with the lower 3% to 5% overall incidence reported by the NIH. The same study identified cultural differences in stimulant prescribing: by fifth grade, 18% to 20% of white boys were prescribed methylphenidate, while rates for other ethnicities were significantly lower (LeFever, 1359).

One of the more reliable studies was conducted in 2005 by the U.S. Centers for Disease Control and Prevention (CDC). This survey examined the number of children reported by their parents in 2003 to have been, or ever to have been, diagnosed with ADHD. The CDC found that the prevalence of ADHD was approximately 7.8% nationally but varied considerably across socioeconomic groups and geographic locations. The lowest incidence, 5%, was reported in Colorado, and the highest, 11%, was reported in Alabama. California, at 5.34%, had one of the lowest reported incidences. The same report indicated that only about half of children aged 4 to 17 who were diagnosed with ADHD actually took medication for the disorder. The highest prevalence for medication treatment was among children aged 9 to 12 years (CDC, p. 842).

Interestingly, the prevalence of reported ADHD symptoms increased with age, becoming highest for males aged 16 years and females aged 11 years, and was lowest for preschool children. The highest rates were also noted among English-speaking, non-Hispanic, and insured children. In addition, rates were most prevalent in families in which the most highly educated adult had a high school diploma, and lower in families where the most educated adult had either more or less than a high school diploma. Families with incomes below the poverty line were also more likely to report a child with ADHD (CDC, p. 844).

Data from the National Health Interview Survey (NHIS) similarly indicate that in 2001–2004, 7.7% of children ages 5 to 17 were reported to have been diagnosed with ADHD. Nine percent of White non-Hispanic children, 8% of Black non-Hispanic children, 2% of Asian non-Hispanic children, and 4% of Hispanic children were reported to have the disorder. Almost 13% of White non-Hispanic children living in families with incomes below the poverty level were reported to have ADHD — the highest of any group. Two to three times more boys than girls are diagnosed with ADHD (Pastor, p. 206).

Although not a primary cause, "family environment adversity factors (e.g., high degree of psychosocial stress, maternal mental disorder, paternal criminality, low socioeconomic status, foster care) have been linked to increased rates of ADHD" (Dopheide, p. 2).

Conclusion

ADHD is a disorder that affects 3% to 5% of school-aged children and may persist into adulthood. Evaluation by an experienced clinician who uses objective ratings from multiple informants across different settings is important for a reliable diagnosis. Once a diagnosis is confirmed, a treatment plan can be developed that also accounts for co-occurring conditions. "Common comorbid conditions include oppositional-defiant disorder, major depression, anxiety disorders, learning disability, and Tourette's disorder. The presence of comorbid conditions can increase the likelihood of ADHD chronicity" (Plitzka, p. S50).

Several validated rating scales exist that are designed for optimal diagnostic assessment. A clinician with specialized expertise in child and adolescent neurodevelopment and behavior is best positioned to generate a reliable diagnosis of ADHD. Because children are highly reactive to their environment:

It is crucial to enlist multiple informants — such as parents, teachers, siblings, children, and caregivers — and to rate symptoms across multiple settings. A child must exhibit at least six out of the nine symptoms of inattention or hyperactivity-impulsivity, or both, that are maladaptive and inconsistent with his or her developmental level. The symptoms must be present in multiple settings over a period of six months and have an onset by age seven before a diagnosis is confirmed (Goldman, p. 111).

Examining the incidence of ADHD from 1997 through 2007, with the aid of statistics from reliable sources and organizations, it is evident from the available literature that accurate rates are difficult to establish, though general increases have been reported — as they were in the years leading up to 1997. Whether these numbers reflect a genuine growth in the number of school-aged children with ADHD, or a growth in the reporting of children believed to have ADHD, may never be fully resolved. However, most reliable sources employ standard screening definitions, as noted above. By studying reported incidences — which vary by location — it may nonetheless be possible to determine whether the average number of school-aged children with ADHD has increased over the past decade.