The diagnostic validity of attention-deficit/hyperactivity disorder

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Abstract

Despite considerable research, the validity of attention-deficit/hyperactivity disorder (ADHD) remains controversial. This paper summarizes the results of a comprehensive review of the internal and external validity of ADHD as defined in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Results indicate that for most individuals DSM-IV ADHD is a valid disorder in the sense that it is associated with significant impairment in social, academic, and occupational functioning and increased risk of accidental injury across the life span. Additional research is needed, however, to clarify the diagnostic validity of the hyperactive-impulsive type and the discriminant validity of the combined and inattentive subtypes. Other areas in need of further study include potential modifications to the diagnostic conceptualization of the inattentive subtype, developmental trajectories of the subtypes, and methods to address cross-informant diagnostic inconsistencies. Such research is likely to benefit from an etiologically informed approach to examining heterogeneity both across and within subtypes.

Introduction

Despite considerable research, there is continuing controversy regarding the nature and validity of the syndrome termed attention-deficit/hyperactivity disorder (ADHD) in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; [1]). Although substantial evidence has accumulated to support the diagnostic validity of ADHD (e.g. [2], [3], [4]), some argue that ADHD symptoms may simply describe the exuberant behavior of normal children (e.g. [5]). Others accept that some children with ADHD have a valid disorder, but contend that weaknesses in the current diagnostic criteria cause some children to be diagnosed inappropriately (e.g. [6]).

Interpretation of studies of the validity of ADHD is further complicated by changes to the diagnostic criteria for ADHD in each successive edition of the DSM (see [4] for a summary of the implications of these changes). The diagnostic criteria for DSM-IV ADHD incorporated separate lists of nine symptoms of inattention and nine symptoms of hyperactivity-impulsivity, and defined three diagnostic subtypes based on differential elevations on these symptom dimensions ([1], [7]). The predominantly inattentive type describes individuals with maladaptive levels of inattention only, the predominantly hyperactive-impulsive type is characterized by maladaptive levels of hyperactivity-impulsivity alone, and the combined type describes individuals with maladaptive levels of both inattention and hyperactivity-impulsivity.

Due to the continuing controversy regarding the validity of ADHD, we recently completed a comprehensive meta-analysis of 114 published studies of DSM-IV ADHD to evaluate the internal and external validity of the DSM-IV ADHD symptom dimensions and subtypes [118]. Space constraints for this special issue preclude a comprehensive review of these studies. Therefore, in this paper, we first describe the criteria a disorder must meet to be considered valid, and then summarize the key findings from the meta-analysis in the text and in Fig. 1, Fig. 2. In a final section, we examine the implications of these results for the DSM-IV model of ADHD and highlight several keys remaining questions regarding the validity and nosology of ADHD.

Section snippets

Validity of mental disorders

As described in more detail elsewhere in this special issue [8], the criteria, which must be met for a mental disorder to be considered valid, have been the focus of considerable discussion (e.g. [4], [8], [9], [10], [11], [12], [13], [14]). These authors have considered an extensive range of important issues, including the role of theory in the development of diagnostic criteria (e.g. [10]), the utility of a dimensional versus categorical conceptualization of mental disorders (e.g. [14]), the

Factor analyses

Exploratory and confirmatory factor analyses of parent and teacher ratings in 16 independent samples of over 15,000 children and adolescents consistently support the DSM-IV model incorporating separate inattention and hyperactivity-impulsivity symptom dimensions (e.g. [17], [18]; reviewed by [118]. All 18 DSM-IV ADHD symptoms loaded on their predicted factors in virtually all studies. Moreover, several studies found that the DSM-IV inattention and hyperactivity-impulsivity factors emerged even

DSM-IV symptom dimensions

In the DSM-IV field trials for the disruptive behavior disorders ([33]), regression analyses were conducted to assess the associations between DSM-IV inattentive and hyperactive-impulsive symptoms and several indices of functional impairment, controlling for symptoms of oppositional defiant disorder (ODD), conduct disorder (CD), anxiety disorders, and depressive disorders. The number of inattentive behaviors was not related to ratings of global adaptive functioning completed by the child's

Gender ratio

More boys than girls met symptom criteria for DSM-IV ADHD in all population-based samples (mean male: female ratio=2.7: 1; [118]). In all but one of these studies, the male to female ratio was lower for the inattentive type than the combined type (and the hyperactive-impulsive type in some cases). Due to the relatively small samples in many of these studies, however, the difference in gender ratios was often not statistically significant. To obtain adequate statistical power to test more

DSM-IV symptom dimensions

Ratings of hyperactivity-impulsivity and inattention symptoms by both parents and teachers are reliable and internally consistent, and nearly all symptoms load primarily on their specified factor in most samples. Both symptom dimensions are associated with multiple aspects of global, academic, and social impairment in rigorously controlled analyses, providing support for the concurrent validity of each symptom dimension. Although inattention and hyperactivity-impulsivity symptoms are associated

Directions for future research

In this final section, we highlight several keys remaining questions regarding the validity of ADHD, and describe future research directions that may help to address these questions.

Summary and conclusions

Existing data provide strong converging evidence that for most individuals DSM-IV ADHD is a reliable diagnosis that is associated with important aspects of functional and neurocognitive impairment after controlling a wide range of variables that are often confounded with the diagnosis. Thus, similar to previous definitions of ADHD ([2]), these results suggest that DSM-IV ADHD is not a construct that inappropriately labels as abnormal a set of behaviors that are upsetting to parents and teachers

Acknowledgements

The authors were supported in part during the preparation of this manuscript by NIH grants P50 HD-27802, F32 MH 12100, R01 MH62120, and R01 MH63941, and by a Big 12 Faculty Fellowship from the University of Colorado, Boulder. We thank Benjamin B. Lahey, Bruce F. Pennington, Joel T. Nigg, Keith McBurnett, and Nomita Chhabildas for their helpful comments on an earlier version of this manuscript.

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