Overview

Attention-deficit/hyperactivity disorder (ADHD) is one of the most common childhood-onset psychiatric disorders. It is distinguished by symptoms of inattention, hyperactivity, and impulsivity. ADHD may be accompanied by learning disabilities, depression, anxiety, conduct disorder, and oppositional defiant disorder. The etiology of ADHD is unknown, and the disorder may have several different causes. Investigators have studied, for example, the relation of ADHD to elevated lead levels, abnormal thyroid function, morphologic brain differences, and EEG patterns. With current public awareness of ADHD, pediatricians and health care providers are reporting increases in referral rates of children with suspected ADHD. Numerous rating scales and medical tests for evaluation and diagnosis of ADHD are available, with mixed expert opinion on their usefulness.

The Agency for Health Care Policy and Research sponsored development of this technical review to summarize current scientific evidence from the literature on the prevalence of ADHD and on the value of various evaluation methods. The following questions provided a framework for the analysis:

  1. What percentage of the U.S. general population aged 6 to 12 years has ADHD? Of those with ADHD, what percentage has one or more of the following comorbidities: learning disabilities, depression, anxiety, conduct disorder, and oppositional defiant disorder?
  2. What percentage of children aged 6 to 12 years presenting at pediatricians’ or family physicians’ offices in the United States meets diagnostic criteria for ADHD? Of those with ADHD, what percentage has one or more of the following comorbidities: learning disabilities, depression, anxiety, conduct disorder, and oppositional defiant disorder?
  3. What is the accuracy (i.e., sensitivity, specificity, positive predictive value) and reliability (i.e., inter/intra-rater agreement) of behavioral rating screening tests for ADHD compared with a reference standard?
  4. What is the prevalence of abnormal findings on selected medical screening tests commonly recommended as standard components of an evaluation of a child with suspected ADHD?

Diagnostic screening tests, as analyzed under questions 3 and 4, were of two types: behavioral rating scales and medical screening tests. The behavior rating scales selected for consideration consisted of both ADHD-specific scales and “broad-band” scales designed to screen for various symptoms including ADHD symptoms. The medical screening tests considered included commonly recommended tests that are standard components of an evaluation of a child with suspected ADHD: electroencephalography, lead concentration level testing, thyroid hormone level testing, hearing and vision screening, imaging tests, neurological screening, and continuous performance tests (CPTs).

Reporting the Evidence

The evidence on ADHD prevalence and diagnosis reported here was gathered from 87 published articles and 10 behavioral scale manuals. Studies must have been peer-reviewed and published in the English language between 1980 and 1997. These 97 sources were identified during searches of the databases MEDLINE and PsycINFO and from reference lists in review articles, research study articles, and a draft guideline on ADHD obtained from the American Academy of Child and Adolescent Psychiatry currently in development; recent journal publications; citations suggested by American Academy of Pediatricians members; and a database of bibliographies on studies that used or evaluated the Child Behavior Checklists (CBCL). Abstracts of more than 4000 identified citations were reviewed, from which 507 articles and 10 manuals were retrieved and subjected to further consideration. The published studies had to be soundly designed and conform to specified inclusion and exclusion criteria to qualify for consideration.

Methodology

Data from the 97 accepted articles/manuals were abstracted, tabulated systematically, and subjected to statistical analysis. A multiple logistic regression model with random effects was used to analyze simultaneously for the effect of age, gender, diagnostic tool, and setting. This model accommodates the fact that each study estimated ADHD rates under slightly different conditions. The analysis was done using the EGRET software.

Summary Findings

The significant findings derived from the analysis are summarized below.

Prevalence of ADHD in General Population

  • Gender, diagnostic tool (DSM-III or DSM-III-R), and setting (community or school setting) are significant contributors to the ADHD rate, but age (5 to 9 years versus 10 to 12 years) is not a significant factor.
  • ADHD prevalence is much higher when academic and behavioral functioning impairment criteria are not considered (16.1 % without impairment criteria versus 6.8% with). Boys have higher rates of ADHD than do girls.

Prevalence of Comorbid ADHD in General Population

  • One-third of children diagnosed with ADHD also qualify for a diagnosis of oppositional defiant disorder (ODD).
  • One-fourth of children diagnosed with ADHD also qualify for a diagnosis of conduct disorder (CD).
  • Less than one-fifth of children with ADHD also have a depressive disorder.
  • More than one-fourth of children with ADHD qualify for a diagnosis of anxiety disorder.
  • Almost one-third of children with ADHD also have more than one comorbid condition.
  • Overall, the prevalence rates of comorbid ADHD are high. Estimates of the prevalence rates of various comorbid conditions in children with ADHD range from 12.36 percent (learning disorders) to 35.15 percent (conduct disorder).

Prevalence of ADHD in Pediatric Clinic Setting

  • Results on prevalence of ADHD in a pediatric clinic setting are varied. A 1997 study finds prevalence conforms to that of the general population; a 1988 study shows much smaller prevalence.

Prevalence of Comorbid ADHD in Pediatric Clinic Setting

  • Results on prevalence of comorbid ADHD in a pediatric clinic setting are varied. A 1997 study finds a high prevalence, similar to that in the general population; a 1988 study gives much smaller rates.

Behavior Rating Scales, ADHD-Specific

  • The Conners Rating Scales, 1997 Revision, contain two highly effective indices for discriminating between ADHD children and normal controls. The Barkley School Situations Questionnaire is less effective. These results are based on studies conducted under ideal conditions; actual performance of the scales in physicians’ offices is expected to be poorer.
  • Hyperactivity subscales that effectively discriminate between ADHD children and normal controls include DSM-III-R SNAP and Conners Abbreviated Teacher Questionnaire (CATQ, HI). The ACTeRS scale performed poorly. These results are based on studies conducted under ideal conditions; actual performance of the scales in physicians’ offices is expected to be poorer.
  • An inattention subscale that effectively discriminates between ADHD children and normal controls is the DSM-III-R SNAP checklist. The ACTeRS scale performed poorly. These results are based on studies conducted under ideal conditions; actual performance of the scales in physicians’ offices is expected to be poorer.
  • An impulsivity subscale that effectively discriminates between ADHD children and normal controls is the DSM-III-R SNAP checklist.

Broad-Band Behavioral Rating Scales

  • None of the broad-band scales analyzed—the CPCL/4-18-R Total Problem Scale, DSMD Total Problem Scale, CPRS-R:L Global Problem Index, and CTRS-R:L Global Problem Index—effectively discriminate between referred and nonreferred children. Thus they are not useful as tools to detect clinical-level problems in children presenting at a pediatrician’s office.
  • Externalizing, internalizing, and adaptive functioning scales did not effectively detect referred versus nonreferred children.

Medical Screening Tests

  • Analysis of six studies on the relation between elevated lead levels and ADHD showed that lead levels are not useful as a general diagnostic tool for ADHD. This is strengthened by the fact that ADHD prevalence appears to be increasing even as lead levels in the population appear to be decreasing.
  • Analysis of four studies showed no relation between abnormal thyroid function and ADHD. Thus, the evidence does not support the use of tests of thyroid function to screen for ADHD.
  • Analysis of seven imaging studies of the brain (CT, CAT, and MRI) that were performed to detect morphologic differences in brain structures of children with ADHD yielded sparse and diverse evidence. Thus none of the imaging procedures analyzed is considered useful as a screening or diagnostic tool for ADHD.
  • Eight studies of electroencephalogram (EEG) patterns and ADHD found no serious EEG abnormalities in ADHD children, although many studies found significant differences in brain wave activity between ADHD children and normal controls. The heterogeneity of results across studies indicates the EEG should not be routinely used as a screening tool for ADHD.
  • Evidence from studies of neurological screening tests did not yield any clues to the etiology of ADHD. Thus these tests are not deemed effective for screening ADHD.
  • Continuous performance tests measure impulsivity, inattention, and vigilance. Statistical analysis of studies using these tests indicated that CPTs would not serve as useful screening tools for ADHD.

Future Research Needs

  • Continued work to gather data on prevalence of ADHD using the following factors lacking in much of the work already done: DSM-IV, use of both genders as subjects, rates of ADHD--Primarily Inattentive Type, and wider-scale studies across regions of the country or across countries using the same criteria.
  • Comparison studies to assess the ability of broad-band behavior checklists to discriminate between clinical and non-clinical samples (those studies available at this time have only presented results of the ability of these tests to discriminate between referred and nonreferred samples). Clinically severe problems are present in both of those groups, as are subclinical problems.
  • Continued work in the area of magnetic resonance imaging and PET, when possible, to continue to explore structural and functional differences in the brains of children diagnosed with ADHD and each of the types of ADHD.