EVANS ET AL. DETERMINANTS OF PROTOTYPICALITY JUDGMENTS DETERMINANTS OF DIAGNOSTIC PROTOTYPICALITY JUDGMENTS OF THE PERSONALITY DISORDERS Diana L. Evans, PhD, James D. Herbert, PhD, Rosemary O. Nelson-Gray, PhD, and Brandon A. Gaudiano, MA We evaluated the impact of three factors that have been suggested to be important determinants of the diagnostic process pertaining to personal- ity disorders: (a) the number of features representative of a personality disorder category; (b) the extent to which those features are typical of the category, and (c) the dominance or proportion of category features to the total number of features. Thirty-two clinical psychologists evaluated 12 profiles of hypothetical patients in which these factors were varied factorially. The results revealed strong effects of typicality and domi- nance, but no effects for number. Implications for the assessment and classification of personality disorders are discussed. Recent years have witnessed a growing interest in the classification of per- sonality disorders. Most current nosological systems, including recent edi- tions of the Diagnostic and Statistical Manual of Mental Disorders (DSM; American Psychiatric Association, 1980, 1987, 1994) are rooted largely in classical models of categorization. If all members of a classical category pos- sess the same set of necessary and sufficient features, it follows that all cat- egory members are equally good and representative instances of the category, and equally poor and unrepresentative examples of other catego- ries. According to the classical model, category membership is inherently clear-cut, with homogeneity within categories, clearly demarcated bound- aries, and heterogeneity between categories. These assumptions, however, do not reflect the more complex reality of many psychological concepts. Such models, in which a list of necessary and sufficient criteria define cate- gory membership, have been found to be problematic in relation to many psychological concepts, including the personality disorders (Cantor & Mischel, 1977; Lakoff, 1987; Rosch, 1973, 1978). The personality disorders defy the assumptions of classical categorization in several ways. These in- clude the high degree of heterogeneity within each disorder, the fact that 95 Journal of Personality Disorders, 16(1), 95-106, 2001 © 2002 The Guilford Press From the Delaware Family Center, Wilmington (D. L. E.); MCP Hahnemann University (J. D. H. and B. A. G.); and the University of North Carolina at Greensboro (R. O. N-G.). Gratitude is expressed to Dr. John Livesley for providing data that made this study possible and to the clinicians who participated in this study. Address correspondence to Diana L. Evans, PhD, Delaware Family Center, 3608 Lancaster Pike, Wilmington, DE 19805; E-mail: drevans@comcast.net