RANDY W. KAMPHAUS, PhD, is Distinguished Research Professor of Educational Psychology and Instructional Technology at The University of Georgia, Athens. He is an expert in the field of child and adolescent assessment and the author of several books on the topic. He is also coauthor of the BASC-II (Behavior Assessment System for Children, Second Edition), a widely used assessment instrument.

JONATHAN M. CAMPBELL, PhD, is Associate Professor of Educational Psychology and Instructional Technology at The University of Georgia, Athens. His research and clinical interests involve assessment and differential diagnosis of autism spectrum disorders as well as understanding typical peers’ perceptions of autism. He has authored several articles in the area of intelligence test interpretation and serves on the editorial boards for the Journal of Psychoeducational Assessment and Journal of Pediatric Psychology.

Psychodiagnostic Assessment of Children

Dimensional and Categorical ApproachesBy Randy W. Kamphaus

John Wiley & Sons

Copyright © 2006 Randy W. Kamphaus
All right reserved.
ISBN: 978-0-471-21219-5

Chapter One

Classification and Diagnosis Concepts

Randy W. Kamphaus, Ellen W. Rowe, Erin T. Dowdy, and Cheryl N. Hendry

Defining Classification and Diagnosis

Psychological constructs are more enduring than diagnostic systems. This premise serves as an organizing principle underlying this text about the process of identifying children and adolescents who need a service: educational, health, mental health, prevention, monitoring, or any other type of service that promotes children’s adjustment to their context of development.

Prerequisite to the process of service delivery is classification, a fundamental, continuously unfolding task that is relevant to all sciences, including the applied clinical process of making a mental health diagnosis. Biological taxonomies exist for classifying various animals and plants according to both common and distinct characteristics. Classification, due to its overarching nature, is a more important activity for a clinician to master than diagnosis-a far more restrictive term. Classification, for example, may lead to the provision of a variety of services, whereas diagnosis is designed to lead to identification and treatment of a disorder-in this text, a mental illness. Classification, the broader term, serves many purposes, diagnostic or otherwise, not the least of which is allowing for natural phenomena, be they disorders or theoretical constructs, to be better defined and measured to enhance our understanding of them.

Diagnosis, the type of classification that is the focus of this text, may be considered a specialized type of classification, one concerned with the categorization of diseases. Although psychiatric diagnostic processes were initiated long ago (Kamphaus, 2001), modern psychiatric diagnosis began with the work of Emil Kraepelin who proposed that a system be created for classifying mental illnesses according to their symptoms, causes (or etiologies), and course (progression of symptomatology). As in the medical sciences where conditions such as heart disease and high blood pressure are classified as separate diseases in psychiatric classification, disorders such as borderline personality disorder are classified separately from schizophrenia or panic disorder.

In spite of various objections and its imperfect nature (Kamphaus & Frick, 2002), the majority of mental health professionals concur that the basic purposes and inherent advantages of classification support its use and further development (Cantwell, 1996). Related to this assumption, Blashfield (1998) described five primary purposes for classification in psychopathology that also serve to illustrate its utilitarian properties:

1. Creation of a common professional nomenclature

2. Organization of information 3. Clinical description

4. Prediction of outcomes and treatment utility

5. The development of concepts upon which theories may be based

These goals, although sound and pragmatic, have yet to be achieved by any one classification system. The predominant diagnostic classification schemes do attempt to provide a common nomenclature, organize information, and clinically describe syndromes or patterns of behavior. Nevertheless, the reliability and validity of prevailing models have not been demonstrated adequately, nor has a clear line of research established expediency with regard to treatment and theory development (Kamphaus & Frick, 2002).

Categorical and Dimensional Methods

Two primary models of diagnostic classification have been presented in the psychopathology literature, categorical and dimensional. Categorical models are dichotomous, inferential in nature, involving the identification of qualitative differences in behavior that are based on clinical observations and careful history taking. The dichotomous nature of categorical approaches deems that an individual either has or does not have a disorder as long as predetermined criteria for that disorder are met. To date, categorical approaches such as the Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text revision (DSM-IV-TR; American Psychiatric Association, 2000) and the Individuals with Disabilities Education Act (IDEA) are used most frequently in health and education, perhaps due in part to tradition and relative ease of application.

In comparison, dimensional classification methods are quantitative and empirical in nature, adopting the assumption that there are a number of behavior traits that all individuals possess in varying degrees that exist along a continuum. These traits or dimensions of behavior are typically derived from measures (e.g., behavior rating scales) through the use of multivariate statistical procedures such as cluster analysis, latent profile or class analysis, or factor analysis (Kamphaus & Frick, 2002). It has not been clearly demonstrated that either of these classification approaches optimally meets the criteria for the five purposes of diagnostic classification as outlined by Blashfield (1998).

The relative value of categorical or clinical-inferential, for example, the DSM-IV-TR (American Psychiatric Association, 2000) and dimensional or empirical, for example, Edelbrock and Achenbach (1980), classification methods has been frequently debated (Fletcher, 1985). However, an increasing body of literature has described the advantages of dimensional models (LaCombe, Kline, Lachar, Butkus, & Hillman, 1991). For example, Achenbach and McConaughy (1992) noted that the yes/no nature of categorical methods does not necessarily account for children whose problems vary in degree or severity. As a result, the shift between “normalcy” and psychopathology cannot be well understood with categorical methods since most high prevalence problem behaviors in children, such as inattention and hyperactivity, are not classifiable when below diagnostic threshold levels. Substantial evidence is emerging to suggest that child behavior problems such as inattention, hyperactivity, depression, and conduct problems, in fact, fall along continua in the population. Therefore, the continuous nature of these child behaviors is more appropriately measured with dimensional scales (Hudziak et al., 1998) rather than with categorical systems (Scahill et al., 1999).

Although not fully incorporated in popular diagnostic schemes, empirically based dimensional classification approaches have demonstrated their usefulness in the study of psychopathology. For example, dimensional approaches have demonstrated more predictive validity than categorical approaches (Fergusson & Horwood, 1995), as well as statistical reliability (Cantwell, 1996). Such methods also minimize the need for clinical judgment and inference (Haynes & O’Brien, 1988), provide greater sensitivity to the presence of comorbid conditions (Caron & Rutter, 1991), and have the ability to depict multiple symptom patterns in a given individual simultaneously (Cantwell, 1996). Further, and perhaps most importantly, the use of dimensional, person-oriented approaches to identify subtypes or clusters of individuals can lead to more efficient, streamlined subtype-specific intervention and prevention services (Achenbach, 1995; Bergman & Magnusson, 1997).

In one sense, a dimensional approach to classification can be viewed simply as another means of translating underlying latent traits into categories (e.g., internalizing/externalizing behaviors), thereby offering only a communicative alternative to existing classification schemes such as the DSM-IV. This point of view suggests that the ultimate goal of classification or diagnosis, the categorization of individuals into homogeneous groups with similarities, is shared by proponents of both categorical and dimensional methods, and arguments that these approaches are entirely distinct are simplistic.

Psychiatric Diagnostic Classification

Psychiatric classification models seek to place disorders into discrete categories as is characteristic of the DSM-IV-TR. The DSM-IV was published in 1994 and is currently the most widely used method of psychiatric classification in the United States (Beutler & Malik, 2002). The first DSM was published in 1952 by the American Psychiatric Association and included three main categories of psychopathology: mental deficiency, functional disorders, and organic brain symptoms. In 1968, the DSM was revised to include 11 major diagnostic categories (DSM-II) and in 1980 the third edition introduced a multiaxial system, the inclusion of explicit criteria, and many unsubstantiated theoretical inferences were removed. The DSM-III-R (American Psychiatric Association, 1987) emphasized empirical literature and the DSM-IV continued with this emphasis on empirical findings (Scotti & Morris, 2000). The DSM-IV reportedly made modest improvements in the reliability and validity of several diagnostic categories, but reliability estimates for many disorders of childhood and adolescence remain inadequate (Nathan & Langenbucher, 1999). The DSM-IV is recognized to be a categorical or taxonomic system of classification (Arend, Lavigne, Rosenbaum, Binns, & Christoffel, 1996) and is concerned with classifying mental disorders-significant distress, functional impairment, and/or special risk (House, 1999). This approach uses rules to determine membership in a category. Using these decision rules, disorders are seen as being either present or absent (Blashfield, 1998). While it appears that improvements have been made in the DSM, some have asserted that the categorical nature of this system has been shown to impede progress toward a more accurate system of classification (Jensen et al., 1993).

Characteristics of Psychiatric (Categorical) Diagnosis

First, diagnosis is made based on the presence of marker symptoms or deviant signs that define a syndrome (DSM-IV-TR, American Psychiatric Association, 2000). Each diagnostic category has a characteristic and unique set of symptoms or signs that are qualitatively different from “normal.” Cancer cells, for example, are cells that differ qualitatively from healthy ones. Similarly, paranoia differs from caution, conducts disorder from mischief, anxiety disorder from occasional worry, clinical depression from normal bereavement, and social phobia from shyness, in quality. Qualitative differences are assessed via structured diagnostic and unstructured patient interviews, and history taking. An adolescent patient may be seen by a clinician for tearfulness and crying, loneliness, inability to sleep, and poor appetite accompanied by weight loss. These are all potential symptoms of depression but through historical interview it could be determined that their duration has been about 10 days and their onset was abrupt. Upon still further questioning, the clinician may discover that the patient broke off a long-term romantic relationship that apparently precipitated these problems. Although the patient experiences waves of sadness, she or he continues to enjoy the company of friends and has a generally optimistic outlook. In fact, the patient may state that she or he desires some medication just until the feelings of sadness pass. She or he is mostly concerned now about getting some sleep in order to be able to function better at work or school. This patient’s expectations for improvement belie the presence of “negative affectivity” that is commonly associated with depression (Kamphaus & Frick, 2002). As the patient’s history unfolds, it becomes increasingly clear that the quality of this individual’s symptomatology differs from that of depression in duration and intensity, thus causing the clinician to be unwilling to classify or diagnose this symptom pattern as a case of depression.

Formal psychometric tests are less valuable for identifying qualitative differences in symptomatology necessary for making a DSM diagnosis leading to dependence in psychiatric diagnosis on interview methods of assessment. The mental status examination (see Kamphaus & Frick, 2002) is characteristic of psychiatric diagnosis and is used as a means for identifying qualitative differences in symptomatology. It is not “scored” or submitted to any type of quantitative analysis; not even the mathematical process of addition of symptoms. The method uses questions to clarify the nature of symptomatology. A child patient, for example, may report that he or she “hears things.” The child might remark that, “I hear someone telling me to do bad things.” After further questioning the clinician may learn that the child often worries about the bully in his classroom who threatens him in an effort to convince him to be disruptive in class. This child’s explanation for “hearing voices” is not unlikely given that psychotic disorders are relatively rare in the population. This “innocent” response is therefore qualitatively different than a case of hearing voices that would suggest the presence of psychotic symptomatology in childhood. Such a response would be something like, “I hear terrorists telling me to kiill my friends. I’m scared because they will not stop. I hear this all day long most days. I can’t get it out of my head. I am afraid I will hurt someone because I think that if I do this then maybe they won’t talk to me any more.” Interview methods are ideal for clarifying the meaning of, and qualitative differences in, symptomatology.

Psychiatric syndromes are also mutually exclusive (e.g., mental retardation and autism, versus Asperger’s syndrome) but potentially comorbid or co-occurring (e.g., diabetes and heart disease, Attention-Deficit /Hyperactivity Disorder and Tourette’s syndrome, Conduct Disorder and depression). The assumption of distinctness is consistent with another assumption of psychiatric diagnosis-syndromes are presumed to be pathogenically distinct as well (i.e., to have differing etiologies). Not only do syndromes have presumed differing etiologies, they also have differing outcomes (e.g., morbidity differs significantly for stomach ulcers versus stomach cancer), and prognoses (e.g., schizophrenia is more debilitating versus dyslexia). Depression has a higher morbidity rate than dyslexia due to the higher risk of suicide associated with the former. In the case of psychiatric diagnosis, other outcomes may substitute for the rare occurrence of death. School drop out, criminality, substance abuse, and elevated risk for developing a more severe psychiatric disorder may serve as proxies for morbidity. Prognoses may differentiate mental health disorders on the basis of chronicity and intensity of services needed. Mental retardation and autism are examples of disorders with greater chronicity and continuing impairment, whereas phobias and separation anxiety disorder may not be chronic, nor are they as likely to require residential care or other more invasive services.

Psychiatric diagnosis, like general physical diagnosis, is categorical or dichotomous in that one either has the disorder or not (e.g., Attention-Deficit/Hyperactivity Disorder [ADHD], irritable bowel syndrome, clinical depression). One cannot be mildly, moderately, or severely pregnant, for example. Severity of symptoms along a continuum is not directly measured although it is “estimated” by the clinician. An exception is that the global assessment of functioning (GAF) code of the DSM system is used by the psychiatric clinician to rate severity of functional impairment. More commonly, however, DSM criteria do not exist to differentiate “severe” from “mild” ADHD, Conduct Disorder, generalized anxiety disorder, and so on.

Severity is not easily determined when interview methods are used as the primary method for diagnosis because they are not as amenable to quantitative analysis, an essential characteristic of a severity scale. Some aspects of physical diagnosis are amenable to quantitative measurement and the disorder can be rated by severity. Vision, disorders of height, and obesity are some examples. Generally, however, the DSM and IDEA classification systems do not apply diagnoses that are either based on or present classifications for severity.

(Continues…)

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