Presenting ADHD Symptoms, Subtypes, and Comorbid Disorders in Clinically Referred Adults With ADHD

Presenting ADHD Symptoms, Subtypes, and Comorbid Disorders in Clinically Referred Adults With ADHD

Timothy E. Wilens, MD; Joseph Biederman, MD; Stephen V. Faraone, PhD; MaryKate Martelon, MPH; Diana Westerberg, BA; and Thomas J. Spencer, MD

Objective: Despite the increasing presentation of attention-deficit/hyperactivity disorder (ADHD) in adults, many practitioners remain reluctant to assess individuals for ADHD, in part related to the relative lack of data on the presenting symptoms of ADHD in adulthood. Comorbidity among adults with ADHD is also of great interest due to the high rates of psychiatric comorbidity, which can lead to a more persistent ADHD among adults.

Method: We assessed 107 adults with ADHD of both sexes (51% female; mean ± SD of 37 ± 10.4 years) using structured diagnostic interviews. Using DSM-IV symptoms, we determined DSM-IV subtypes. The study was conducted from 1998 to 2003.

Results: Inattentive symptoms were most frequently endorsed (> 90%) in adults with ADHD. Using current symptoms, 62% of adults had the combined subtype, 31% the inattentive only subtype, and 7% the hyperactive/impulsive only subtype. Adults with the combined subtype had relatively more psychiatric comorbidity compared to those with the predominately inattentive subtype. Women were similar to men in the presentation of ADHD.

Conclusion: Adults with ADHD have prominent inattentive symptoms of ADHD, necessitating careful questioning of these symptoms when evaluating these individuals.

J Clin Psychiatry 2009;70(11):1557-1562

© Copyright 2009 Physicians Postgraduate Press, Inc.

Submitted: October 3, 2008; accepted January 9, 2009 (doi:10.4088/JCP.08m04785pur).

Corresponding author: Timothy E. Wilens, MD, Pediatric Psychopharmacology Unit, Massachusetts General Hospital, YAW 6A, 55 Fruit Street, Boston, MA 02114 ([email protected]).

Adults with attention-deficit/hyperactivity disorder (ADHD) are increasingly presenting for evaluation and treatment of their disorder, reflective of the clinical awareness of the chronicity of the disorder1-3 and identification of the disorder in adults with other psychiatric disorders.4-6 Despite this awareness, many practitioners remain reluctant to assess and subsequently treat individuals for ADHD7 in part because of the relative lack of data on the presenting symptoms of ADHD in adulthood.

Prospectively collected data suggest that prominent ADHD symptoms persist in approximately one-half of childhood cases into young adulthood8 and that 4% to 5% of adults may have ADHD.6 Longitudinal studies also show a developmental influence on ADHD symptoms.8-10 These data suggest a decay of ADHD symptoms over time with more persistence of the inattentive symptoms of ADHD relative to the hyperactive/impulsive symptoms.8-11 In support of this notion, using Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R) criteria, we previously reported higher levels of inattentive symptoms compared to hyperactive/impulsive symptoms in a sample of adults with ADHD.12 However, those data were derived from DSM-III-R, necessitating replication using Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria and subtypes to better understand the current symptomatic presentation of adults with ADHD.

The literature also suggests that children with psychiatric comorbidities such as conduct disorder may be at higher risk for the persistence of specific subtypes of ADHD,10,13 highlighting the important influence of co-occurring psychiatric disorders on the presentation of ADHD in older age groups. Additionally, sex differences may also affect the presentation of ADHD over time. For example, studies of girls with ADHD suggest lower rates of conduct disorder relative to boys with ADHD14,15 that may translate into less hyperactivity and impulsivity in adulthood. However, the effect of sex on the symptom presentation of ADHD in adults remains understudied.

Given that the diagnosis of ADHD is established through clinical history,16-18 a better understanding of manifested symptoms in adults with ADHD has the potential to increase the diagnostic precision of clinicians. To better understand the symptom profile of adults with ADHD, we systematically assessed DSM-IV ADHD symptoms in a large group of adults with the disorder. We secondarily evaluated the influence of psychiatric comorbidity, sex, and age on the presentation of ADHD in adults. Based on the literature,12 we hypothesized that inattentive symptoms would be more prominent relative to hyperactive/impulsive symptoms in a sample of adults with childhood-onset and persistent ADHD. We further hypothesized that psychiatric comorbidity would be more common with the combined subtype relative to the inattentive subtype of ADHD.

METHOD

Subjects

Men and women between the ages of 18 and 55 years were eligible to become probands for the study. Exclusion criteria were deafness, blindness, psychosis, inadequate command of the English language, or a full-scale IQ less than 80 as measured by the IQ estimated from the block design and vocabulary subtests of the Wechsler Adult Intelligence Scales-Revised.38 No ethnic or racial group was excluded. We recruited potential probands with ADHD through advertisements in the greater Boston area and referrals to adult ADHD clinics. The institutional review board at Massachusetts General Hospital approved the study, and subjects provided signed informed consent.

Assessment Measures

Trained lay interviewers, blind to ascertainment status, interviewed all adults with the Structured Clinical Interview for DSM-IV (SCID)19 and modules from the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Epidemiologic Version (K-SADS-E).20,39,40 When we asked questions about childhood disorders, the subjects were first queried about childhood symptoms, and if they were present, they were asked about continuation of these symptoms into adulthood and the emergence of others. Age at onset was defined as the first emergence of impairing symptoms. Before interviewing for the study, interviewers completed a 4-month training program that included mastery of the instruments, learning about DSM-IV criteria, watching training tapes, observing interviews performed by experienced raters, rating several subjects under the supervision of the project coordinator, and completing practice interviews. Throughout the study, they were supervised by board-certified child and adolescent psychiatrists or licensed psychologists. This supervision included weekly meetings and additional consultations, as needed.

During the study, all interviews were audiotaped for random quality control assessments. Final diagnostic assignment was based on the structured psychiatric interview. Initial diagnoses were prepared by the study interviewers and were then reviewed by a diagnostic committee of board-certified child and adolescent psychiatrists or licensed psychologists. The diagnostic committee was blind to each subject’s ascertainment group and diagnoses were made for 2 points in time: lifetime and current (past month). The interviewers had been instructed to take extensive notes about the symptoms for each disorder. These notes and the structured interview data were reviewed by the diagnostic committee so that the committee could make a best-estimate diagnosis, as described by Leckman et al.21 Definite diagnoses were assigned to subjects who met all diagnostic criteria. Diagnoses were considered definite only if a consensus was achieved that criteria were met to a degree that would be considered clinically meaningful. By “clinically meaningful,” we mean that the data collected from the structured interview indicated that the diagnosis should be a clinical concern because of the nature of the symptoms, the associated impairment, and the coherence of the clinical picture.

We computed κ coefficients of agreement by having experienced board-certified child and adult psychiatrists and licensed clinical psychologists diagnose subjects from audiotaped interviews. On the basis of 500 assessments from interviews of children and adults, the median κ coefficient was 0.98. κ coefficients for individual diagnoses were ADHD (0.88), conduct disorder (1.00), major depression (1.00), mania (0.95), separation anxiety (1.00), agoraphobia (1.00), panic (0.95), substance use disorder (1.00), and tics/Tourette’s disorder (0.89).

Statistical Analysis

We conducted analyses on probands who had a current diagnosis of ADHD. Categorical data were analyzed using Pearson χ2 test and when necessary, Fisher exact test. t Tests and 1-way analysis of variance were used to analyze continuous variables, and the Wilcoxon rank sum and the Kruskal-Wallis tests were used to analyze continuous variables that were not normally distributed. An α level of .05 was used to assert statistical significance; all statistical tests were 2-tailed. We calculated all statistics using Stata 10.0 (StataCorp LP, College Station, Texas).

RESULTS

In this sample, there were 107 adults with ADHD of which 49% (n = 52) were male and 51% (n = 55) were female. The mean ± SD age of the sample was 37 ± 10.4 years. Men were significantly younger than women (men, 34 years, women, 39 years; t = 2.8, P < .01). The mean socioeconomic status of the sample, as measured by the Hollingshead Four Factor Index of Social Status,22 was 2.0 ± 0.9 (Table 1). There were no differences in socioeconomic status between sexes or across the subtypes of ADHD.

This was a highly comorbid group of adults: 8% had no psychiatric comorbidity, 10% had a lifetime history of 1 comorbid psychiatric disorder, 14% had 2, 15% had 3, and 53% had 4 or more psychiatric comorbidities. When asked about the level of overall impairment related directly to their ADHD symptoms in the past, 40% (n = 43) of our ADHD sample endorsed severe impairment, 53% (n = 57) moderate impairment, and 7% (n = 7) mild impairment. Likewise, when asked about the level of impairment caused by their ADHD symptoms within the past month, 22% (n = 24) endorsed severe impairment, 50% (n = 54) moderate impairment, and 26% (n = 28) mild impairment.

When specific DSM-IV ADHD symptoms were examined, inattentive symptoms were more frequently endorsed overall than hyperactive symptoms (Figure 1). The most commonly reported inattentive symptoms were “being easily distracted,” “difficulty sustaining attention,” and “difficulty with sustained mental effort.” The most commonly reported hyperactive symptoms were “blurts out answers,” “interrupts or intrudes,” and “fidgets.” Sixty-two percent (n = 66) of adults had the combined subtype, 31% (n = 33) had the inattentive subtype, and 7% (n = 8) had the hyperactive/impulsive subtype. There were no differences between men and women in the total number of endorsed inattentive or hyperactive/impulsive symptoms. However, when each symptom was examined individually, females were significantly more likely to endorse the inattentive symptom of “loses things” (χ2 = 7.5, P < .01). When the sample was split into 2 groups at the median age of 38 years, there were no differences between age groups in the total number or type of endorsed inattentive and hyperactive/impulsive symptoms.

Adults with a combined type of ADHD had significantly higher rates of lifetime conduct disorder, bipolar disorder, and psychosis compared to those with the inattentive and the hyperactive/impulsive subtypes (Table 2). From the post hoc analysis, we determined that adults with the combined type had a significantly greater prevalence of conduct disorder and bipolar disorder when compared to only the inattentive subtype. In regard to academic functioning, there were no significant differences in the number of individuals who repeated a grade, took a special class, and had extra help across the ADHD subtypes.

We further examined our data to determine whether sex was related to psychiatric comorbidity. Men had significantly higher lifetime rates of comorbid conduct disorder and alcohol abuse (P < .01), while women had significantly higher rates of comorbid dysthymia, panic disorder (P < .05), agoraphobia, simple phobia, and generalized anxiety disorder (P < .01).

DISCUSSION

The results of the current study indicate that adults with ADHD have prominent symptoms of inattention. On the basis of DSM-IV criteria, 93% of adults with ADHD had either the predominately inattentive or combined subtypes—indicative of prominent behavioral symptoms of inattention in adults. Psychiatric comorbidity was more commonly found in subjects with hyperactivity/impulsivity as part of their adult presentation.

Similar to our results, studies of the prevalence of DSM-IV subtypes in clinically referred children and adolescents with ADHD in the DSM-IV field trials23 show that the combined type is the most prevalent type of ADHD (66%), followed by the inattentive (33%) and the hyperactive/impulsive types (8%). Moreover, our results are similar to community-based studies in children reporting high rates of the inattentive subtype (5.4%), followed by the combined (3.6%) and hyperactive/impulsive (2.4%) types.24 In our sample, the overwhelming majority of adults with ADHD endorsed prominent inattentive symptoms that were subsumed in either the inattentive or combined subtypes (93%). Our findings are consistent with aggregate studies in which the majority of children and adolescents met criteria for a subtype of ADHD with inattention.23 That inattentive symptoms predominate also support findings of impaired neuropsychological functioning, working memory, and executive functioning in adults with ADHD.25

The high rates of symptoms of inattention relative to hyperactivity/impulsivity are consistent with prospectively derived data in clinically and epidemiologically based samples of children, adolescents, and young adults with ADHD in which decreases in the hyperactive and impulsive symptom clusters compared to the inattentive clusters were evident over time.8-10,26-29

We found that psychiatric comorbidity was more common in context to the combined and inattentive-only subtypes. It may be that psychiatric comorbidity is a marker of more severe ADHD as exemplified by more symptoms reflected in the combined subtype.30 Of interest, high rates of psychiatric comorbidity have been reported in adults with ADHD.6,31,32 Psychiatric comorbidity has also been shown to be associated with more persistent ADHD13 and with prominent hyperactive/impulsive symptoms in adults with ADHD.33 More specifically, in the current study, adults with a combined type of ADHD had significantly higher rates of lifetime conduct disorder, bipolar disorder, and psychosis compared to those with the inattentive subtype, mirroring findings from a separate dataset showing more hyperactivity and impulsivity in adults with ADHD who had comorbid bipolar disorder relative to those without bipolar disorder and ADHD.33

Given that this sample was largely derived from clinical referral, and because both clinically and epidemiologically derived samples of adults with ADHD have been shown to have high rates of co-occurring psychopathology,6,31,32 it is difficult to disentangle whether higher specific symptom clusters as well as higher symptom counts are associated with comorbidity, or if comorbidity skews symptom counts. Further analysis should be done on specific endorsed symptoms in longitudinal studies. These aggregate data suggest the need to carefully examine adults with more pronounced symptoms of ADHD for other psychiatric comorbidity. Moreover, psychiatric comorbidity with ADHD may predict a more persistent form of ADHD.33

Interestingly, we found no sex differences in ADHD symptoms. In the sample with equal sex distribution, both sexes had high rates of attentional dysfunction relative to hyperactivity/impulsivity. Moreover, similar to previous reports in adults,34 we found that men with ADHD had higher lifetime comorbidity with conduct disorder and alcohol abuse relative to women with ADHD. Conversely, women had higher rates of comorbid dysthymia, panic disorder, agoraphobia, simple phobia, and generalized anxiety disorder compared to men. These findings are consistent with data derived from longitudinal studies of girls growing up, which highlight more similarities than dissimilarities in the core ADHD and general and cognitive functioning between the sexes.35 However, notable differences in specific comorbidities between the sexes remain.

The results of this study need to be tempered against their substantial limitations. The findings are based in part on observations from both a nonreferred and clinically referred population and, therefore, may not generalize to all adults with ADHD. Also, because we assessed adults who met only 6 of the 9 child-based ADHD diagnostic criteria, our sample represents a more severe group of ADHD adults and may not generalize to all adults with ADHD. The symptoms reported by these adults may not have been entirely accurate given the retrospective recall required of past symptoms. However, previous studies have documented the validity of using retrospective recall in the diagnosis of adults with ADHD.16,18,36,37

Despite these limitations, findings from the current study support previous work with separate samples that showed that the vast majority of adults with ADHD present prominent symptoms of inattention, independent of sex. Compared to adults with the inattentive subtype of ADHD, those with the combined subtype had higher rates of psychiatric comorbidity. Given the high prevalence of ADHD occurring in mental health and substance abuse domains, more emphasis on the inattentive aspects of ADHD needs to be highlighted when making the diagnosis.

Disclosure of off-label usage: The authors have determined that, to the best of their knowledge, no investigational information about pharmaceutical agents that is outside US Food and Drug Administration−approved labeling has been presented in this article.

Author affiliations: Pediatric Psychopharmacology Clinic and Adult ADHD Program, Massachusetts General Hospital and Harvard Medical School, Boston (Drs Wilens, Biederman, and Spencer and Mss Martelon and Westerberg) and Departments of Psychiatry and of Neuroscience and Physiology, The State University of New York Upstate Medical University, Albany (Dr Faraone).

Financial disclosure: Dr Wilens receives grant support from Abbott, McNeil, Eli Lilly, National Institutes of Health (National Institute on Drug Abuse; NIH [NIDA]), Merck, and Shire; is a speaker for the speakers’ bureaus of Eli Lilly, McNeil, Novartis, and Shire; is a consultant for Abbott, AstraZeneca, McNeil, Eli Lilly, NIH (NIDA), Novartis, Merck, and Shire; and has a published book with Guilford Press, Straight Talk About Psychiatric Medications for Kids. Dr Biederman is currently receiving research support from Alza, AstraZeneca, Bristol-Myers Squibb, Eli Lilly, Janssen, McNeil, Merck, Organon, Otsuka, Shire, the National Institute of Mental Health (NIMH), and the National Institute of Child Health and Human Development; is currently a consultant/advisory board member for Janssen, McNeil, Novartis, and Shire; is currently a speaker for the speakers’ bureaus of Janssen, McNeil, Novartis, Shire, UCB Pharma, Inc, Fundacion Areces, Medice Pharmaceuticals, and the Spanish Child Psychiatry Association; and in previous years has received research support, consultation fees, or speaker’s fees from Abbott, AstraZeneca, Celltech, Cephalon, Eli Lilly, Esai, Forest, GlaxoSmithKline, Gliatech, NARSAD, NIDA, New River, Novartis, Noven, Neurosearch, Pfizer, Pharmacia, The Prechter Foundation, Shire, The Stanley Foundation, UCB Pharma, and Wyeth. Dr Faraone has received consulting fees, been on the advisory boards for, or been a speaker for Eli Lilly, Shire, McNeil, Janssen, Novartis, and Pfizer and has received research support from Eli Lilly, Pfizer, Shire, and the NIH. Dr Spencer receives research support from Shire, Cephalon, Eli Lilly, GlaxoSmithKline, Janssen, McNeil, Novartis, Pfizer, and NIMH; has been a speaker for the speakers’ bureaus of Shire, Eli Lilly, GlaxoSmithKline, Janssen, McNeil, and Novartis; and is on the advisory board for Shire, Cephalon, Eli Lilly, GlaxoSmithKline, Janssen, McNeil, Novartis, and Pfizer. Mss Martelon and Westerberg have no personal affiliations or financial relationships with any commercial interest to disclose relative to the article.

Funding/support: This study was supported by National Institutes of Health grants RO1 DA12945 (Dr Wilens) and K24 DA016264 (Dr Wilens).

REFERENCES

1. Weiss G, Hechtman L, Milroy T, et al. Psychiatric status of hyperactives as adults: a controlled prospective 15 year follow-up of 63 hyperactive children. J Am Acad Child Psychiatry. 1985;24(2)211-220. PubMed

2. Wilens TE, Faraone SV, Biederman J. Attention-deficit/hyperactivity disorder in adults. JAMA. 2004;292(5):619-623. PubMed doi:10.1001/jama.292.5.619

3. Mick E, Faraone SV, Biederman J, et al. The course and outcome of ADHD. Prim Psychiatry. 2004;11(7):42-48.

4. Alpert JE, Maddocks A, Nierenberg AA, et al. Attention deficit hyperactivity disorder in childhood among adults with major depression. Psychiatry Res. 1996;62(3):213-219. PubMed doi:10.1016/0165-1781(96)02912-5

5. Schubiner H, Tzelepis A, Milberger S, et al. Prevalence of attention-deficit/hyperactivity disorder and conduct disorder among substance abusers. J Clin Psychiatry. 2000;61(4):244-251. PubMed

6. Kessler RC, Adler L, Barkley R, et al. The prevalence and correlates of adult ADHD in the United States: results from the National Comorbidity Survey Replication. Am J Psychiatry. 2006;163(4):716-723. PubMed doi:10.1176/appi.ajp.163.4.716

7. Kessler RC, Hwang I, LaBrie R, et al. DSM-IV pathological gambling in the National Comorbidity Survey Replication. Psychol Med. 2008;38(9):1351-1360. PubMed doi:10.1017/S0033291708002900

8. Biederman J, Faraone S, Mick E. Age dependent decline of ADHD symptoms revisited: impact of remission definition and symptom subtype. Am J Psychiatry. 2000;157(5):816-817. PubMed doi:10.1176/appi.ajp.157.5.816

9. Achenbach TM, Howell CT, McConaughy SH, et al. Six-year predictors of problems in a national sample of children and youth: I. Cross-informant syndromes. J Am Acad Child Adolesc Psychiatry. 1995;34(3):336-347. PubMed doi:10.1097/00004583-199503000-00020

10. Hart EL, Lahey BB, Loeber R, et al. Developmental change in attention-deficit hyperactivity disorder in boys: a four-year longitudinal study. J Abnorm Child Psychol. 1995;23(6):729-749. PubMed doi:10.1007/BF01447474

11. Gammon GD, Brown TE. Fluoxetine and methylphenidate in combination for treatment of attention deficit disorder and comorbid depressive disorder. J Child Adolesc Psychopharmacol. 1993;3(1):1-10.

12. Millstein RB, Wilens TE, Biederman J, et al. Presenting ADHD symptoms and subtypes in clincially referred adults with ADHD. J Atten Disord. 1997;2(3):159-166. doi:10.1177/108705479700200302

13. Biederman J, Faraone S, Milberger S, et al. Predictors of persistence and remission of ADHD into adolescence: results from a four-year prospective follow-up study. J Am Acad Child Adolesc Psychiatry. 1996;35(3):343-351. PubMed doi:10.1097/00004583-199603000-00016

14. Hinshaw SP. Preadolescent girls with attention-deficit/hyperactivity disorder: I. Background characteristics, comorbidity, cognitive, and social functioning, and parenting practices. J Consult Clin Psychol. 2002;70(5):1086-1098. PubMed doi:10.1037/0022-006X.70.5.1086

15. Faraone SV, Biederman J, Mick E, et al. A family study of psychiatric comorbidity in girls and boys with attention deficit hyperactivity disorder. Biol Psychiatry. 2001;50(8):586-592. PubMed doi:10.1016/S0006-3223(01)01146-5

16. Adler L, Cohen J. Diagnosis and evaluation of adults with ADHD. In: Spencer T, ed. Psychiatric Clinics of North America. Philadelphia, PA.: Saunders Press; 2004: 187-201.

17. Wender P. The Hyperactive Child, Adolescent, and Adult: Attention Deficit Disorder Through the Lifespan. New York, NY: Oxford University Press; 1987.

18. Stein MA, Sandoval R, Szumowski E, et al. Psychometric characteristics of the Wender Utah Rating Scale (WURS): reliability and factor structure for men and women. Psychopharmacol Bull. 1995;31(2):425-433.

19. First M, Spitzer R, Gibbon M, et al. Structured Clinical Interview for DSM-IV Axis I Disorders. Washington, D.C.: American Psychiatric Press; 1997.

20. Ambrosini PJ. Historical development and present status of the schedule for affective disorders and schizophrenia for school-age children (K-SADS). J Am Acad Child Adolesc Psychiatry. 2000;39(1):49-58. PubMed doi:10.1097/00004583-200001000-00016

21. Leckman JF, Sholomskas D, Thompson D, et al. Best estimate of lifetime psychiatric diagnosis: a methodological study. Arch Gen Psychiatry. 1982;39(8):879-883. PubMed

22. Hollingshead AB. Four Factor Index of Social Status. New Haven, CT: Yale University Press; 1975.

23. Lahey BB, Applegate B, Barkley RA, et al. DSM-IV field trials for oppositional defiant disorder and conduct disorder in children and adolescents. Am J Psychiatry. 1994;151(8):1163-1171. PubMed

24. Wolraich ML, Hannah JN, Pinnock TY, et al. Comparison of diagnostic criteria for attention-deficit hyperactivity disorder in a county-wide sample. J Am Acad Child Adolesc Psychiatry. 1996;35(3):319-324. PubMed doi:10.1097/00004583-199603000-00013

25. Seidman L, Doyle A, Fried R, et al. Neuropsychological functioning in adults with attention-deficit/hyperactiity disorder. In: Spencer T, ed. Adult ADHD, Psychiatric Clinics of North America: New York, NY: Elsevier Science; 2004:261-282.

26. Murphy K, Barkley RA. Prevalence of DSM-IV symptoms of ADHD in adult licensed drivers: implications for clinical diagnosis. J Atten Disord. 1996;1(3):147-161. doi:10.1177/108705479600100303

27. Mannuzza S, Klein RG, Bessler A, et al. Adult outcome of hyperactive boys: educational achievement, occupational rank, and psychiatric status. Arch Gen Psychiatry. 1993;50(7):565-576. PubMed

28. Levy F, Hay D, McStephen M, et al. Attention-deficit hyperactivity disorder: a category or a continuum? genetic analysis of a large-scale twin study. J Am Acad Child Adolesc Psychiatry. 1997;36(6):737-744. PubMed doi:10.1097/00004583-199706000-00009

29. Faraone SV, Biederman J, Mick E. The age-dependent decline of attention-deficithyperactivity disorder: a meta-analysis of follow-up studies. Psychol Med. 2006;36(2):159-165. PubMed doi:10.1017/S003329170500471X

30. Faraone SV, Biederman J, Friedman D. Validity of DSM-IV subtypes of attention-deficit/hyperactivity disorder: a family study perspective. J Am Acad Child Adolesc Psychiatry. 2000;39(3):300-307. PubMed doi:10.1097/00004583-200003000-00011

31. McGough JJ, Smalley SL, McCracken JT, et al. Psychiatric comorbidity in adult attention deficit hyperactivity disorder: findings from multiplex families. Am J Psychiatry. 2005;162(9):1621-1627. PubMed doi:10.1176/appi.ajp.162.9.1621

32. Sobanski E, Bruggemann D, Alm B, et al. Subtype differences in adults with attention-deficit/hyperactivity disorder (ADHD) with regard to ADHD-symptoms, psychiatric comorbidity and psychosocial adjustment. Eur Psychiatry. 2008;23(2):142-149. PubMed doi:10.1016/j.eurpsy.2007.09.007

33. Wilens TE, Biederman J, Wozniak J, et al. Can adults with attention-deficit hyperactivity disorder be distinguished from those with comorbid bipolar disorder? findings from a sample of clinically referred adults. Biol Psychiatry. 2003;54(1):1-8. PubMed doi:10.1016/S0006-3223(02)01666-9

34. Biederman J, Faraone SV, Spencer TJ, et al. Gender differences in a sample of adults with attention deficit hyperactivity disorder. Psychiatry Res. 1994;53(1):13-29. PubMed doi:10.1016/0165-1781(94)90092-2

35. Biederman J, Mick E, Faraone SV, et al. Influence of gender on attention deficit hyperactivity disorder in children referred to a psychiatric clinic. Am J Psychiatry. 2002;159(1):36-42. PubMed doi:10.1176/appi.ajp.159.1.36

36. Ward MF, Wender PH, Reimherr FW. The Wender Utah rating scale: an aid in the retrospective diagnosis of childhood attention deficit hyperactivity disorder. Am J Psychiatry. 1993;150(6):885-890. PubMed

37. Adler LA, Faraone SV, Spencer TJ, et al. The reliability and validity of self- and investigator ratings of ADHD in adults. J Atten Disord. 2008;11(6):711-719. PubMed doi:10.1177/1087054707308503

38. Wechsler D. Manual for the Wechsler Adult Intelligence Scale-Revised. San Antonio, TX: The Psychological Corporation; 1981.

39. Orvaschel H. Psychiatric interviews suitable for use in research with children and adolescents. Psychopharmacol Bull. 1985;21(4):737-745. PubMed

40. Orvaschel H. Schedule for Affective Disorder and Schizophrenia for School-Age Children-Epidemiologic Version. Fort Lauderdale, FL: Nova Southeastern University, Center for Psychological Studies; 1994.