Theory-Based Reasoning in Clinical Psychologists

Theory-Based Reasoning in Clinical Psychologists Nancy S. Kim (nancy.s.kim@yale.edu) Department of Psychology, Yale University; 2 Hillhouse Avenue New Haven, CT 06520 USA Woo-kyoung Ahn (woo-kyoung.ahn@vanderbilt.edu) Department of Psychology, Vanderbilt University; 534 Wilson Hall Nashville, TN 37240 USA Abstract Progress in science is marked by the formation of theories that explain a body of observations. Contrary to this guiding philosophy, clinical psychologists have prescribed to an atheoretical system of diagnostic reasoning since 1980. We report two studies demonstrating that clinicians have not internalized atheoretical reasoning despite the system’s widespread acceptance. The results show that clinicians’ own theories about disorders significantly affect their diagnoses of hypothetical patients and memory for symptoms. Clinicians are cognitively driven to form and apply theories to observations despite decades of deliberate training, practice, and pressure to reason atheoretically. Introduction Philosophers of science have argued for decades that scientific progress is delineated not merely by the amassing of observations, but rather by the formation of broad principles that organize and explain these observations in a cohesive manner (Hempel, 1965). Evolutionary theory, for example, is regarded as a revolutionary advance in organismic biology in large part because it provides a deeper structure for a scientific taxonomy of living things, moving away from classification based on superficial features. Data are measured and considered within the larger structure of this overarching theory. Similarly, the human mind constantly seeks out underlying rules and principles that make sense of incoming data concerning the surrounding world. Adults (Murphy & Medin, 1985), children (Gelman, 2000; Keil, 1989), and even infants (Marcus, Vijayan, Rao, & Vishton, 1999) spontaneously extract and apply underlying organizing principles and abstract rules that go beyond surface features. In this way, the human mind forms categories and concepts based on its theories about the surrounding world (Carey, 1985). Atheoretical versus theory-based reasoning In contrast, the current Diagnostic and Statistical Manual of Mental Disorders (APA, 1994), prescribes an atheoretical approach to diagnosing mental disorders (Follette & Houts, 1996). Most mental disorders lack a single universally acknowledged pathogenesis, which in the past led to unreliability between clinicians in diagnosis. The DSM-IV's (APA, 1994) widely acclaimed solution is to eliminate theory use altogether when making a diagnosis, incorporating instead checklists of symptoms compiled by a panel of experts. In doing so, it represents each disorder as a list of unrelated symptoms, ignoring the causal relations between symptoms that are a fundamental aspect of theory representations (Carey, 1985). For most disorders, the DSM-IV (APA, 1994) states that a subset of the list is sufficient for a diagnosis regardless of which combination of symptoms appears, thereby assuming that all symptoms in the list are equally central to the disorder. For example, any 2 of the following 5 symptoms warrant a diagnosis of schizophrenia, according to the DSM-IV: hallucinations, delusions, disorganized speech, grossly disorganized or catatonic behavior, and negative symptoms. Since eliminating any overt mention of an underlying theory for the taxonomy two decades ago (APA, 1980), the DSM system has become widely accepted in the U.S., forming the core of research, clinical assessment, diagnosis, and treatment in psychopathology. Research funding, journal titles, and health care reimbursements are all organized by, and dependent on, use of the categories defined by the DSM-IV (APA, 1994). Has the DSM system succeeded in internalizing atheoretical reasoning in clinicians? An atheoretical approach would suggest that experienced clinicians, after years of emphasizing use of the DSM system, will come to embody its prescription of atheoretical reasoning (APA, 1994). In contrast, the theory-based approach would suggest that clinicians, despite such emphasis on the elimination of theory, are still influenced by their own idiosyncratic theories about disorders when reasoning about them (Medin, 1989). The two approaches were differentiated by testing for the presence or absence of the causal status effect, a specific mechanism by which theory-based reasoning occurs (Ahn, 1998; Ahn, Kim, Lassaline, & Dennis,