Clinicians' conceptual use of comorbidity

Abstract

Diagnostic overlap, termed comorbidity, is a common occurrence in psychopathology. However, the current classification system for mental disorders (DSM-IV-TR; APA, 2000) does not explicitly address how diagnostic concepts should be combined. The DSM assumes an additive model where the study of how humans combine concepts in general would predict some degree of multiplicative combination. The study described herein used the methods of cognitive psychology to examine practicing clinicians’ conceptualizations of comorbid cases. Two samples of clinicians drawn from the Association of Behavioral and Cognitive Therapies (ABCT; n = 48) and licensed psychologists in the state of Florida (n = 25) were asked to describe three disorders and their combinations using a predetermined list of symptoms. The primary evidence of a multiplicative model of combination was the presence of overextensions, or symptoms which occurred in a combination that were not a part of either constituent disorder. Results indicated that clinicians included overextensions in non-zero amounts demonstrating use of some level of a multiplicative model in contrast to the additive model assumed in the DSM. These findings question the clinical utility of the current diagnostic system and suggest that the current paradigm of descriptive psychopathology may not be congruent with clinicians’ conceptualizations.