Chapter 19: Costa and McCrae: Five Factor Model of Personality
Chapter 19: Costa and McCrae: Five Factor Model of Personality
Part 3: Personality in Real Life
There remains debate as to exactly how personality disorders should be classified. This issue is more than just a matter of curiosity, since our entire conception of personality disorders is an essential factor in how we approach their treatment. As perhaps the most widely accepted and scientifically validated trait perspective on normal personality, it stands to reason that the Five-Factor Model (FFM) ought to also provide a basis for classifying abnormal personality and, in particular, the personality disorders. Thus, Costa and Widiger (1994) brought together a group of experts, including Theodore Millon, to address personality disorders within the context of the FFM.
The DSM-III thru DSM-V use diagnostic categories for the personality disorders, whereas the FFM suggests a dimensional approach. The categorical approach has several advantages. It is relatively easier to conceptualize disorders as either having them or not, clinicians are familiar with the current categories, and when clinical decisions are categorical they tend to be consistent. However, the dimensional approach offers the advantages of not being arbitrary in defining specific symptom cut-off points for a diagnosis, they allow for retaining information on those patients who just miss the cut-off point for a diagnosis (and could, therefore, simply be classified as not having the disorder), and the dimensions are more flexible than a categorical diagnosis. More importantly than just speculating on advantages and disadvantages, however, is that the majority of empirical data seems to support the dimensional approach (Widiger & Frances, 1994). For example, borderline personality disorder patients do not show a specific profile on the Minnesota Multiphasic Personality Inventory (MMPI), but rather a nonspecific elevation across most scales. Diagnosis is typically made following a clinical evaluation including an interview. A similar challenge faces clinicians using the NEO-PI (the assessment tool specifically designed for the FFM), but useful and relevant data are available from looking at the specific trait scores within factors, particularly within the factor neuroticism (Trull & McCrae, 1994). In addition, factor analysis on the dimensions of personality disorder yielded results that fit very well with the FFM, with several aspects of personality disorder (but not all) again being linked to neuroticism (Schroeder, Wormworth, & Livesley, 1994). It is important to remember, however, that the very idea of using a dimensional approach is based, in part, on an assumption:
…If one assumes that disordered personality is qualitatively different from normal personality, then the inclusion of a dimensional model of personality may be insufficient or inappropriate for investigation. If one assumes that disordered personality reflects quantitative differences in the manifestation or severity of norm