The official classification system for formulating psychiatric diagnoses in the United States is the Diagnostic and statistical manual of mental disorders, 4th edition
; American Psychiatric Association, 1994
). In this system of nomenclature, the diagnostic criteria for each mental disorder specify the number and severity (intensity, frequency, duration, etc.) of symptoms needed to fulfill criteria. For example, for Attention Deficit Hyperactivity Disorder (ADHD), 6 of 9 Inattention behaviors and/or 6 of 9 Hyperactivity-Impulsivity behaviors must have been exhibited “often” for at least 6 months. In addition to this Symptom Criterion, nearly all mental disorders in DSM-IV
(mood, anxiety, dissociative, personality, etc.) include an explicit Impairment Criterion. For ADHD, this criterion states, “There must be clear evidence of clinically significant impairment in social, academic, or occupational functioning” (APA, 1994
, p. 84). Despite this requirement, some investigators have based prevalence estimates on the Symptom Criterion, alone. Gadow et al. (2000)
studied 600 10- to 12-year-old Ukrainian children, and compared rates of “ADHD” to those obtained among 443 U.S. children. The authors note, “Because symptom-based rating scales typically do not assess the full list of diagnostic criteria for ADHD (e.g., age at onset or duration of symptoms, degree of impairment), screening cutoff scores are not equivalent to a clinical diagnosis” (p. 1522). Pineda et al. (1999)
studied 540 4- to 17-year-old Colombian children to estimate the prevalence of “probable AD/HD”. They refer to their failure to employ the Impairment (and other) Criterion as “a major limitation in interpreting (their) results” (p. 459).
One reason why some investigators have ignored the Impairment Criterion is because it is assumed that, if a certain number of behaviors is exhibited frequently, then those behaviors will have a deleterious functional impact. However, several child studies have reported that, when the Impairment Criterion is applied, rates of ADHD diminish substantially. In their review of 50 epidemiological studies, Faraone, Sergeant, Gillberg, and Biederman (2003)
found that studies that reported ADHD rates based on symptoms, alone, and symptoms plus functional impairment, invariably found lower rates for the latter estimate (16.1% vs. 6.8%, 15.8% vs. 0.2%, etc.).
Two reports specifically have addressed the relationship between the Symptom and Impairment Criteria in the DSM-IV
diagnosis of ADHD. Gordon et al. (2006)
studied this association in four, large-scale ADHD research projects (three involving children, and one including adults). Across studies, the average correlation between systematically assessed ADHD symptoms and impairment accounted for less than 10% of the variance. Furthermore, the number of subjects diagnosed as having ADHD based on symptoms, alone, decreased by 77% when the Impairment Criterion additionally was required.
Gathje, Lewandowski, and Gordon (2008)
studied 314 5- to 17-year-olds seen at an ADHD clinic. Two symptom measures (rated by parents) and six impairment measures (rated by parents or teachers) were obtained. Nine of the 12 symptom-impairment correlations were below .30, explaining less than 9% of the variance. Based on symptom measures, alone, 60% of subjects were identified as having ADHD. This proportion dropped to 19% when impairment was required.
To our knowledge, only two studies (same investigator) assessed the relationship between ADHD symptoms and impairment in adults. Barkley (described in Gordon et al., 2006
) evaluated 158 19- to 25-year-olds who had been diagnosed as having ADHD between ages 4 and 12. At follow-up, DSM-III-R
(American Psychiatric Association, 1987
) and DSM-IV
symptoms were based on interviews with parents, and measures of impairment were based on interviews with subjects (e.g., self-reported number of driving tickets), high school transcripts (e.g., grade point average), official arrest records (e.g., number of felony arrests), and employer ratings (on job performance). The mean correlation of number of symptoms with specific measures of impairment (based on over 50 coefficients) was .25, with none of the correlations accounting for more than 25% of the variance. In a subsequent analysis of these data, Barkley and colleagues (2006)
recoded impairment measures to form dichotomous scores (impaired, not impaired) on 18 items (e.g., failed to graduate high school, fired from 2 or more jobs, 3 or more arrests, and has trouble keeping friends). Scores were totaled (0–18) to form an overall index of impairment. Symptom-impairment correlations (all significant at p < .001) were .45 for number of inattention behaviors, .53 for number of hyperactive-impulsive behaviors, and .53 for number of all ADHD behaviors. Barkley et al. (2006)
concluded that, although ADHD symptoms may have only a “modest relationship” with any single measure of outcome, the relationship is “moderate or greater” when overall impairment is represented across functional domains. However, even in the subsequent analyses, only 20–28% of the variance is explained.
In a second report on an independent sample, Barkley, Murphy, and Fischer (2008)
studied 146 adults with ADHD, 97 non-ADHD Clinical Controls, and 109 non-ADHD Community Controls (mean ages, 32–38). Individuals in the first two groups were consecutive referrals to an Adult ADHD clinic; Community Controls (described as “relatively normal adults”) were obtained via advertisements. Clinical Controls met criteria for a variety of disorders, but not ADHD. Analyses were conducted on the entire sample, i.e., all groups combined. Two interview impairment measures were studied- number of functional domains showing impairment (6 possible), and clinician rating on the Social and Occupational Functioning Assessment Scale
: Patterson & Lee, 1995
, ranging from 1, grossly impaired to 100, superior functioning). All correlations were high and significant (p < .001): number of domains with- number of inattention behaviors (r = .83), number of hyperactive-impulsive behaviors (r = .70), and number of all ADHD behaviors (r = .84); SOFAS
rating with- number of inattention behaviors (r = − .78), number of hyperactive-impulsive behaviors (r = − .67), and number of all ADHD behaviors (r = − .80). In addition, all subjects who reported experiencing at least 4 of 9 inattentive and/or 4 of 9 hyperactive-impulsive behaviors as often or very often, also reported being impaired in at least one functional domain.
In summary, studies that have systematically assessed the relationship between ADHD symptoms and functional impairment in children, consistently have shown that the association is modest, at best, implying that symptoms and impairment are independent dimensions that cannot be treated as equivalent when diagnosing ADHD. Also, when the Impairment Criterion is ignored, the number of children diagnosed as having DSM-IV ADHD escalates dramatically. However, studies of adults are less consistent. Only two such studies have been conducted, both by the same investigator. One found that, similar to reports in children, the relationship between symptoms and specific measures of impairment was relatively weak (mean r = .25), although somewhat higher when an overall measure of impairment is studied (r = .45–.53). The other study found that this association was very strong (r’s = .67 to .84). Since the implications of misdiagnosis are considerable, concerning who is treated and how, we addressed the relationship between ADHD symptoms and impairment in our adult data set.
With one exception [Barkley et al.’s (2008)
number of functional domains], impairment measures across studies have not been clearly tied to ADHD symptoms. Therefore, it is not known whether the ADHD symptom or some other factor resulted in functional disruption. For example, in his study of children with ADHD followed into adulthood, Barkley (described in Gordon et al., 2006
) included number of arrests as a measure of impaired functioning. It is well established that adults with ADHD show considerable comorbidity (Davidson, 2008
), and that follow-up studies of children with ADHD consistently have reported an increased risk for antisocial personality disorder (Fischer, Barkley, Smallish, & Fletcher, 2002
; Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1993
; Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1998
; Rasmussen & Gillberg, 2000
; Weiss, Hechtman, Milroy, & Perlman, 1985
). It may be that the comorbid antisocial syndrome, rather than the ADHD symptoms, was associated with criminal history. Similarly, other comorbid disorders (e.g., substance use, mood, and anxiety disorders, all of which have been reported at increased rates among ADHD adults) may have contributed to vehicular offenses, decreased work performance, and lower educational attainment in that study. Another example is the SOFAS
rating used by Barkley and colleagues (2008)
. According to these investigators, interviewers were instructed to base this rating on the participant’s social, occupational, and educational functioning, and impairment was understood to be “a direct consequence of the mental and physical health problems of the individual” (p. 133). Therefore, this rating confounded mental and physical problems, and there is no guarantee that the “mental problems” were specific to ADHD.
The purpose of this study is to investigate the relationship between ADHD symptoms and impairment among adults who were diagnosed as having ADHD in childhood. Different from other studies, we used a measure of impairment that was directly tied to each of the three core ADHD symptoms, Inattention, Impulsivity, and Hyperactivity. For each symptom, trained clinicians who were blind to participant status (ADHD proband or non-ADHD comparison) asked respondents whether the symptom “led to any difficulties at home, at work or with other people” during the follow-up interval (approximately 16 years, from age 25 to present). Clinicians rated each symptom on an anchored, 5-point impairment scale ranging from None to Extreme. Based primarily on findings in children, we hypothesized that: (1) symptom and impairment correlations would be modest, and; (2) compared to individuals fulfilling the ADHD Symptom Criterion, a considerable number of subjects would not be diagnosed as having ADHD as adults when impairment was required.