Abstract
Current symptom criteria for ADHD in the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; American Psychiatric Association, 1994) require that the individual exhibit a criterion number of symptoms of inattention, hyperactivity-impulsivity, or both (depending on ADHD subtype). The threshold number of six of nine possible symptoms required for clinical significance in either or both of these domains was determined on the basis of the DSM-IV field trials, which identified the cutoff points necessary to optimize detection of individuals with clinically significant impairment (Lahey et al., 1994). It is noteworthy that the field trial included only youth ranging from 4 to 17 years of age. Thus, the DSM-IV criteria for ADHD are exactly the same for children and adults when evaluating neurodevelopmental symptoms known to diminish with age. Heightened awareness regarding the persistence of ADHD into adulthood on one hand (Barkley, Murphy, & Fischer, 2008) coupled with a report attesting to the diminution of hyperactivity-impulsivity over development on the other hand (Biederman, Mick, & Faraone, 2000) indicate the need for research to identify the appropriate cutoff point for adults, which was the purpose of the current study.
To our knowledge, only one previous study has been conducted to identify the appropriate cutoff points for adults on the DSM-IV symptom dimensions. Murphy and Barkley (1996) obtained data on a self-report questionnaire of DSM-IV symptoms of ADHD from 720 adults applying for or renewing drivers’ licenses in Massachusetts. Based on statistical conventions of “normality,” the authors selected the symptom count that corresponded to a score of 1.5 standard deviations above the mean (93rd percentile) as the threshold of clinical significance. Using this criterion, they found notably lower thresholds for both dimensions of ADHD. The study raised compelling questions about the appropriateness of current standards but relied entirely on an undiagnosed sample drawn from the general population.
The purpose of the current study was to determine if the same or similar results would be obtained for the hyperactive-impulsive dimension by examining symptom frequency in a sample of adults who had been diagnosed as having ADHD. All participants in the current study had been diagnosed as having ADHD according to strict application of DSM-IV criteria using a structured diagnostic interview. Study eligibility criteria allowed for inclusion of individuals with either the predominantly inattentive or combined subtype of ADHD. Thus, all participants met the requirement of at least six of nine inattentive symptoms, but not all participants met the criterion of six of nine hyperactive-impulsive symptoms. All participants in the study had also been screened via a dimensional questionnaire, which ascertained the frequency/severity of the hyperactive-impulsive symptoms relative to the general population of adults of the same gender and age group. Thus, it was possible to identify the subset of individuals with extreme scores relative to the general population on the dimensional measure and cross-reference their symptom counts on the structured interview keyed to DSM-IV. This information could then be used to identify the symptom frequency cutoff point for the DSM-IV set of hyperactive-impulsive symptoms that would capture most of these individuals with empirically verified extreme levels of hyperactivity-impulsivity.
Method
The study was approved by the Human Subjects Review Committee at the institution where the research was conducted, and all participants provided signed, informed consent. The participants comprised 88 adults with ADHD who took part in a treatment outcome study. All met DSM-IV criteria for either combined or predominantly inattentive type. Thus, although inclusion criteria required that all participants meet the criterion of at least six DSM-IV inattentive symptoms, the frequency and severity of hyperactive-impulsive symptoms were free to vary within the sample. Clinical data used in the current study were collected at baseline (before treatment).
Structured Diagnostic Interview
The diagnosis of ADHD was based on the Conners’ Adult ADHD Diagnostic Interview for DSM-IV (CAADID; Epstein, Johnson, & Conners, 2001), conducted by a psychologist or a board-eligible psychiatrist trained to a reliability criterion of .90. This interview is comprised of a detailed inquiry concerning the presence of each of the 18 DSM-IV symptoms in childhood and in adulthood. Each symptom question is followed by standard probes that are specific for child or for adult situations and behaviors. For example, the item “Do you often have trouble remaining seated for extended periods of time?” is probed for adulthood by asking the following follow-up questions: (a) “Do you find it hard to stay in one place for long?” (b) “Do you have difficulty staying seated through a TV show or lecture?” (c) “Do you like to do active things?” and (d) “Do you seek out fast-paced activities?”
After the symptom criteria are examined, the interviewer conducts a detailed inquiry concerning the impact of the reported symptoms on the individual’s functioning, separately in childhood and adulthood, in each of the following domains: academic, social, occupational, and emotional. On the basis of the individual’s responses, the interviewer assigns a rating of impairment on a scale that ranges from 1 (not impaired) to 7 (profoundly impaired), corresponding to the same levels found on the widely used National Institute of Mental Health (NIMH) scale of Clinical Global Impressions (NIMH, 1985).
Dimensional Questionnaire
Individuals were also screened on the Conners’ Adult ADHD Rating Scale–Self-Report: Long Form (CAARS-S:L; Conners et al., 1999; Erhardt, Epstein, Conners, Parker, & Sitarenios, 1999). The CAARS-S:L is a self-report questionnaire that was normed by age (within a 10-year span) and gender on 839 adults in the general population. The questionnaire includes 66 items and nine empirically derived subscales that assess core features of ADHD (DSM-IV inattentive and DSM-IV hyperactive-impulsive symptoms) and associated behavioral characteristics (e.g., problems with self-concept). The DSM-IV scales on the CAARS-S:L are comprised of the inattentive or hyperactive-impulsive symptoms worded exactly as they appear in the DSM-IV (e.g., “I am always on the go as if driven by a motor”). Each item is rated on a scale with the following levels: 0 (not at all), 1 (just a little), 2 (pretty much, often), and 3 (very much, frequently). The sum of the weights assigned to the items on a given scale constitutes the raw score, which is converted to a T-score stratified by age and gender.
Participation in the study required a T-score on the CAARS-S:L of at least 65 (corresponding to 1.5 SD above the mean, equivalent to the 93rd percentile) on the DSM-IV Inattentive subscale of the CAARS-S:L and also on the Inattention/Memory subscale. However, as described, the severity of hyperactivity-impulsivity was free to vary within the sample. For purposes of the current study, we identified from the sample of 88 adults those individuals who were highly elevated (i.e., T-score ≥ 65) on the CAARS-S:L DSM-IV Hyperactive-Impulsive subscale. For these adults, we examined the corresponding number of DSM-IV hyperactive-impulsive symptoms endorsed on the CAADID interview.
Results
Demographic and clinical characteristics of the sample are indicated in Tables 1 and 2, respectively. The mean age of the sample was 41.69 years with the following age distribution: 20% of the sample ranged in age between 23 and 29, 49% ranged in age between 30 and 49, and the remainder (31%) ranged in age between 50 and 63. The impairment scores for the participants ranged between 3 (mildly impaired) and 6 (severely impaired).
Demographic Characteristics
Note: WAIS-III = Wechsler Adult Intelligence Scale–Third Edition.
Clinical Variables
Note: DSM-IV = Diagnostic and Statistical Manual of Mental Disorders–Fourth Edition; CAADID = Conners’ Adult ADHD Diagnostic Interview for DSM-IV; CAARS-S:L = Conners’ Adult ADHD Rating Scale–Self-Report: Long Form.
Of the 88 adults who constituted the sample, 48 (55%) also had empirically elevated severity of hyperactive-impulsive symptoms on the CAARS-S:L relative to the normal population of adults (i.e., equaled or exceeded a T-score of 65 on the DSM-IV Hyperactive-Impulsive subscale on this measure). However, of this subset of adults, only 25 (52%) met the DSM-IV cutoff of six hyperactive-impulsive symptoms on the CAADID. Thus, roughly half of the sample reported significantly elevated hyperactive-impulsive complaints on the CAARS-S:L but did not meet the current six-symptom DSM-IV cutoff on the CAADID structured diagnostic interview. Examination of cumulative frequencies (Table 3) indicated that an alternative cutoff of four hyperactive-impulsive symptoms on the CAADID would capture 39 (81.2%) cases identified by the CAARS-S:L.
Number of DSM-IV Hyperactive-Impulsive Symptoms Endorsed (CAADID) by Participants With T ≥ 65 on the DSM-IV Hyperactive-Impulsive Subscale (CAARS:S-L)
Discussion
Mandating at least six hyperactive-impulsive symptoms as a criterion for diagnosis of ADHD in an adult sample excluded a significant percentage (almost half) of adults who were at least 1.5 SD above the population mean on an age- and gender-normed dimensional measure of hyperactivity-impulsivity (CAARS-S:L). By contrast, a symptom threshold score of four hyperactive-impulsive captured 81% of individuals with elevated scores on the CAARS-S:L.
The study by Murphy and Barkley (1996), referenced previously, ascertained for the inattentive and hyperactive-impulsive dimensions on the DSM-IV the symptom frequency count that corresponded to a point 1.5 SD above the mean within each of three age groups, with results as follows: (a) 17 to 29 years old—four inattentive and five hyperactive-impulsive, (b) 30 to 49 years old—three inattentive and four hyperactive-impulsive, and (c) 50+ years old—two inattentive and three hyperactive-impulsive. Our identification of a cutoff point of four hyperactive-impulsive symptoms thus corroborates the results of Murphy and Barkley for the subsample of those adults in that study, derived from the general population, who were aged 30 to 49 years. Adults aged 30 to 49 years constituted the largest age group (49%) within the sample for the current study. Thus, we confirm the findings of the prior study using a different methodology (yet a comparable age demographic), thereby lending support to their validity.
Also supportive of these conclusions is a study of a population-based sample of 1,813 adults in the Netherlands, which indicated that those adults with four or more inattentive or hyperactive-impulsive symptoms were significantly more impaired than adults with two, one, or no symptoms (Kooij et al., 2005).
In conclusion, the results of this study, combined with previous research, provide a compelling basis for lowering the symptom threshold for hyperactive-impulsive symptoms of ADHD for adults in the DSM-V. Alternatively, dimensional measures, normed by gender and age, may be preferable to the current categorical system for identifying clinically significant levels of ADHD symptoms, including inattention.
Footnotes
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article:The study was supported by NIMH Grant 1R34MH071721 to the first author.