ADHD & ADD: Epidemiologies


compiledby Teresa Binstock for
Generation Rescue
June 2008

ADHD & ADD: Epidemiologies


1. Epidemiology of ADHD [in US, UK, AU]

By National Health and Medical Research Council Government of Austrailia
The National Health and Medical Research Council of Austrailia

There have been widely different prevalence rates reported in both the United States and the United Kingdom for the hyperkinetic disorder, attention deficit disorder with hyperactivity (ADDH) and attention deficit hyperactivity disorder (ADHD). For example the draft ICD-10 (WHO 1988) criteria in the United Kingdom were based on a study by Taylor, Sandberg, Thorley et al (1991), which found a prevalence of 1.7 per cent for hyperkinetic disorder in boys. Hyperkinetic disorder was defined as a score of 1.5 or greater on the hyperactivity- inattentiveness criteria of the Conners Teacher Rating Scale (TRS), together with a score of 1.0 or greater on the hyperactivity scale of the Parent Account of Children's Symptoms (PACS).
       In the United States, ADHD, as defined by the third DSM edition (DSM-III) (American Psychiatric Association 1980), which required observations of symptoms by a parent or teacher, had a prevalence of 6 per cent. ADHD, as defined by the revised third edition, DSM-III-R (American Psychiatric Association 1987) which also allowed a diagnosis at home or at school, was thought likely to have a higher prevalence rate.
       The diagnostic criteria of the most recent classifications for ADHD in DSM-IV (1994), and the research diagnostic criteria of ICD-10 (1993), are almost identical. Both require observation of symptoms in two or more settings (home/school/clinic) and should provide similar prevalence rates in the United Kingdom and the United States (estimated by DSM-IV to be 3-5 per cent). The multiple diagnoses possible in DSM-IV in the presence of co-morbid conditions, compared to the compound diagnoses of ICD-10, may affect prevalence rates. Even small differences in diagnostic procedures can affect rates, which in turn have a powerful effect on the predictive value of diagnostic tests. The advent of DSM-IV Îpredominantly inattentive types of attention deficit disorder (ADD) could, for example, increase trait prevalence rates.
       One reason for the above United States/United Kingdom differences in prevalence rates is that prevalence estimates are arrived at using at least two different methods (Glow 1980; Quay 1979), using either a categorical or a trait (or empirical) approach to diagnosis.
       Australian studies have shown prevalence rates ranging between 2.3 per cent and 6 per cent (Glow 1980) depending on the methodology used. Current epidemiological studies will need to take account of newest DSM edition, DSM-IV (American Psychiatric Association 1994).

Age and gender difference
       In general, boys are rated higher on disruptive behaviour scales (Werry and Hawthorne 1976). Also, incidences of hyperactive problems are usually reported as being 49 times as common in boys than in girls depending on the setting (community or clinic) (DSM-IV 1994). Age differences in DSM-IV subtypes of ADHD have been postulated by Barkley (1995a), but data are not currently available.

Key points - epidemiological data
       Epidemiological data remain imprecise and are influenced greatly by the method of ascertainment. Also, as DSM-IV and ICD-10 have only recently been published, epidemiological data based on these classification systems are not currently available. Most studies show a considerably higher incidence of ADHD in males than in females.

© 2001-2007 National Health and Medical Research Council Government of Austrailia. All Rights Reserved.

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2. The epidemiology of attention-deficit/hyperactivity disorder (ADHD): a public health view

Rowland AS, Lesesne CA, Abramowitz AJ.
Ment Retard Dev Disabil Res Rev. 2002;8(3):162-70.

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurodevelopmental disorder of childhood. However, basic information about how the prevalence of ADHD varies by race/ethnicity, sex, age, and socio-economic status remains poorly described. One reason is that difficulties in the diagnosis of ADHD have translated into difficulties developing an adequate case definition for epidemiologic studies. Diagnosis depends heavily on parent and teacher reports; no laboratory tests reliably predict ADHD. Prevalence estimates of ADHD are sensitive to who is asked what, and how information is combined. Consequently, recent systematic reviews report ADHD prevalence estimates as wide as 2%-18%. The diagnosis of ADHD is complicated by the frequent occurrence of comorbid conditions such as learning disability, conduct disorder, and anxiety disorder. Symptoms of these conditions may also mimic ADHD. Nevertheless, we suggest that developing an adequate epidemiologic case definition based on current diagnostic criteria is possible and is a prerequisite for further developing the epidemiology of ADHD. The etiology of ADHD is not known but recent studies suggest both a strong genetic link as well as environmental factors such as history of preterm delivery and perhaps, maternal smoking during pregnancy. Children and teenagers with ADHD use health and mental health services more often than their peers and engage in more health threatening behaviors such as smoking, and alcohol and substance abuse. Better methods are needed for monitoring the prevalence and understanding the public health implications of ADHD. Stimulant medication is the treatment of choice for treating ADHD but psychosocial interventions may also be warranted if comordid disorders are present. The treatment of ADHD is controversial because of the high prevalence of medication treatment. Epidemiologic studies could clarify whether the patterns of ADHD diagnosis and treatment in community settings is appropriate. Population-based epidemiologic studies may shed important new light on how we understand ADHD, its natural history, its treatment and its consequences. Copyright 2002 Wiley-Liss, Inc.
    PMID: 12216060

3. Epidemiology of ADHD in school-age children

Scahill L, Schwab-Stone M.
Child Adolesc Psychiatr Clin N Am. 2000 Jul;9(3):541-55, vii. 

Attention-Deficit/Hyperactivity Disorder is a relatively common condition of childhood onset and is of significant public health concern. Over the past two decades there have been 19 community-based studies offering estimates of prevalence ranging from 2% to 17%. The dramatic differences in these estimates are due to the choice of informant, methods of sampling and data collection, and the diagnostic definition. This article provides a critical review of the community-based studies on the prevalence of ADHD in children and adolescents. Based on the 19 studies reviewed, the best estimate of prevalence is 5% to 10% in school-aged children. The review also examines age and gender effects on the frequency of ADHD. The article closes with a discussion of psychosocial correlates and patterns of comorbidity in ADHD.
    PMID: 10944656

4: CDC: ADHD: A Public Health Perspective Conference

5. Have there been changes in children's psychosomatic symptoms? A 10-year comparison from Finland

Santalahti P et al.
Pediatrics. 2005 Apr;115(4):e434-42.

OBJECTIVES: The aims of the study were to determine whether the prevalence of children's somatic symptoms, such as headache, abdominal pain, other pain, and nausea and vomiting, changed from 1989 to 1999 and to study the similarity of parents' and children's reports of the child's symptoms. Furthermore, the aims were to explore possible comorbidity in somatic symptoms and to investigate the associations between somatic and psychiatric symptoms. METHODS: Two cross-sectional, representative samples were compared. All children born in 1981 (1989 sample, n = 985) and 1991 (1999 sample, n = 962) and living in selected school districts in southwest Finland served as study samples. The response rate for the 1989 sample was 95% and that for the 1999 sample was 86%. Both children and parents were asked about the children's somatic symptoms, whereas parents, children, and teachers were asked about psychiatric symptoms. To study psychiatric symptoms, the Children's Depression Inventory and Rutter's parent and teacher scales were used. RESULTS: The prevalence of frequent headaches and abdominal pain increased somewhat from 1989 to 1999. Parents often failed to recognize their children's psychosomatic problems. Child-reported somatic symptoms were associated with conduct and hyperactivity symptoms, in addition to a previously well-documented association with depression. In associations between somatic symptoms and psychiatric symptoms, there were some differences between the 1989 and 1999 samples. CONCLUSIONS: In clinical work, questions about somatic and psychiatric symptoms should also be addressed to children themselves, because parents and teachers do not always recognize children's symptoms. When somatic problems are being evaluated, psychiatric symptoms should be asked about, and vice versa. More research is needed to explore the reasons for the increased prevalence of somatic symptoms and their associations with psychiatric symptoms.
PMID: 15805346

Additional topics will be added from time to time

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