Psychological Science is Changing the Way We Think About Mental Disorder
Clinical psychologists are increasingly calling for the discipline to become more empirically guided and less dependent on traditional clinical theories and expertise. This movement toward a clinical science model has already achieved a number of well-publicized goals, including (a) the establishment of clinical science graduate programs and internships, which comprise the Academy of Psychological Clinical Science (APCS) membership, (b) the formation of the Psychological Clinical Science Accreditation System (PCSAS) to evaluate and accredit clinical science training programs, and (c) the promotion of empirically supported treatments for many mental disorders. These advances highlight the shift that clinical psychology is undergoing as it becomes increasingly integrated with the broader field of psychological science. Although these issues are receiving a great deal of attention, psychologists outside of clinical science may be unaware of the strong impact that basic psychological science research is having on another area of the field: changing the way we conceptualize, classify, and diagnose mental disorders. This change is readily apparent in proposed updates for the personality disorders (PDs) section of the Diagnostic and Statistical Manual of Mental Disorders (DSM).
The DSM and Personality Disorders
The DSM, currently in its fourth edition (DSM-IV-TR; American Psychiatric Association, 2000), serves as the primary classification system for psychopathology in the United States and abroad. The DSM-IV is currently undergoing revision to become the DSM-5, scheduled for publication in 2013. Because the DSM is so influential and has such a broad scope — codifying mental disorders, guiding clinical assessment and diagnosis (and therefore a good deal of treatment), and defining many of the constructs examined in clinical research — such revisions need to be based firmly on scientific evidence rather than solely on clinical opinion. Indeed, the DSM-5 promises to be the most research-oriented nosology of psychopathology yet developed.
Fortunately, the evidence being brought to bear in developing DSM-5 is not limited solely to psychiatric and clinical psychology research. Basic, interdisciplinary psychological science is also being incorporated into the new diagnostic manual, including the personality disorders (PDs) section. Currently, the PDs are defined as a set of 10 categorical (i.e., present vs. absent) diagnoses that represent longstanding, inflexible, and pervasive patterns of maladaptive cognition, affectivity, interpersonal functioning, and impulse control. These disorders have a long history: Arising primarily from clinical experience and theory, the precursors to modern PDs were included in the DSM-I, published in 1952. Over the ensuing half-century, however, the accumulation of findings from various fields of psychological science has drawn the definition of these constructs into question. A few of the most influential findings are detailed below.
Weaknesses of the Current Approach
Use of the current approach to PD classification has yielded significant progress, including new ways to assess and treat these disorders, but clinical scientists have noted that this system also has myriad weaknesses. Widiger and Trull (2007) discussed many such limitations of the current PD classification, including (a) high levels of comorbidity (co-occurrence) between putatively distinct disorders, (b) poor coverage of the universe of possible PD content, (c) arbitrary boundaries for distinguishing the presence/absence of a PD, and (d) heterogeneity among individuals with the same PD diagnosis. As an example, let us briefly consider borderline PD, which effectively illustrates several of these limitations. First, borderline PD is highly comorbid with a wide variety of psychopathology, including mood, anxiety, and substance use disorders as well as other PDs (Eaton et al., in press). Second, under DSM-IV-TR’s polythetic system for categorical disorders, patients who meet five or more of the nine borderline PD diagnostic criteria receive the diagnosis, while those who meet four or fewer do not. This assumes a meaningful boundary between four and five meet criteria, although this delineation is largely arbitrary. Finally, the five-of-nine threshold also produces heterogeneity within the diagnosis. For instance, two individuals can share only a single symptom (e.g., “chronic feelings of emptiness”) and receive the same borderline PD diagnosis. This threshold yields 256 different symptom combinations that can result in a diagnosis of borderline PD (Johansen et al., 2004). Clearly, the current system is not optimal.
Structure of Normal Personality
Unlike the DSM system, most personality psychologists have moved away from categorical personality “types” to dimensional structures using continuous traits. Indeed, personality science investigations of the structure of individual differences in normal personality have repeatedly converged on similar structures. The most widely accepted of these trait models of normal personality are the Big Five and the closely related Five-Factor Model (FFM), comprising domain-level traits of neuroticism, extraversion, agreeableness, conscientiousness, and openness to experience. Although the FFM has faced some scrutiny, it represents a consensus structure for many personality psychologists. The FFM also served as a major impetus to consider whether personality pathology could be conceptualized in a similar manner, with a single set of dimensional traits defining the multivariate space in which personality disorder could exist. Finally, it spurred researchers to ask how similar these traits would be to the FFM domains of normal personality.
The shortcomings of the current PD classification system identified by clinical scientists, and the robustness of empirically derived FFM domains of normal personality, suggest that quantitative methods (rather than clinical experience and theory) might produce a more accurate and scientifically defensible taxonomy of PD. Some researchers have designed dimensional instruments to capture personality pathology via empirical methods (e.g., Clark, 1993; Livesley, 1986); others have conducted factor analyses of the current PD diagnoses or criteria (e.g., Nestadt et al., 2006); and still others have attempted to integrate PDs into higher order structures that link them with other syndromes, such as mood, anxiety, and substance use disorders (e.g., Eaton et al., in press). The results are compelling. In general, there seem to be relatively few latent dimensions that capture personality pathology well and replicate across samples and instruments, and these dimensions often appear to represent the extremes of the dimensions of normal personality (Widiger & Simonsen, 2005). This similarity is so marked in many studies that some researchers argue strongly that the FFM itself should be used to capture personality pathology (e.g., Widiger, Costa, & McCrae, 2002).
Toward DSM-5 and Beyond
The Personality and Personality Disorders Work Group, the committee charged with revising the PDs in DSM-5, is now attempting to create an empirically derived PD classification system that integrates these findings from personality, clinical, quantitative, and other areas of psychological science and also proves beneficial to mental health professionals and their patients. The system the Work Group has proposed (available at http://www.dsm5.org) is a unique model that includes a six-dimension structure. These dimensions (and their hypothesized relations to the FFM) are negative emotionality (high neuroticism), introversion (low extraversion), antagonism (low agreeableness), disinhibition (low conscientiousness), compulsivity (high conscientiousness), and schizotypy (which has somewhat unclear associations with openness; see Tackett, Silberschmidt, Krueger, & Sponheim, 2008; Watson, Clark, & Chmielewski, 2008). This structure clearly resembles the FFM in many ways and serves to highlight the influence that basic cross-disciplinary psychological science can have.
In describing the impact of psychological science on PDs in DSM-5, Work Group Chair and psychiatrist Andrew Skodol stated that “the Work Group seeks to integrate basic and clinical sciences with clinical experience to provide a model of personality psychopathology that is both useful in the present and well-positioned to increase our understanding of personality disorders and improve their treatment in the future” (personal communication, August 23, 2010). Another Work Group member, psychologist Robert Krueger, concurred: “Findings from personality trait research, psychometrics, quantitative modeling of psychopathology, and a host of other areas have been instrumental in reformulating personality disorders. DSM-5 will represent a major step toward empirically supported classification of these disorders and will also demonstrate the critical role that basic psychological science research — from multiple areas of the field — must play in informing clinical constructs, taxonomy, assessment, and treatment” (personal communication, August 6, 2010).
This proposed DSM-5 PD system represents an important step toward a classification of mental disorders that is informed by all relevant psychological science research. However, there are even bigger changes on the horizon. The National Institute of Mental Health has begun an effort to classify psychopathology based on observable behavior and neurobiological measures. This project, called the Research Domain Criteria (RDoC), will synthesize data ranging from single gene polymorphisms to complex neural circuits in an attempt to classify mental disorder into an empirically derived system for use in research. Such projects highlight the necessity of interdisciplinary research for conceptualizing mental disorder in the most accurate and informative way. Thus, in both the clinic and the laboratory, broad psychological science research is proving indispensible in efforts to address psychopathology and, in doing so, is also breaking down the artificial barriers between disciplines within the field itself.
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Eaton, N.R., Krueger, R.F., Keyes, K.M., Skodol, A.E., Markon, K.E., Grant, B.F., & Hasin, D.S. (in press). Borderline personality disorder comorbidity: Relationship to the internalizing-externalizing structure of common mental disorders. Psychological Medicine.
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