On the usefulness of measures of normal personality for clinical assessment: evidence of the incremental validity of the Revised NEO Personality Inventory.

As a means of examining the incremental validity of a normal personality measure in the prediction of selected Axis I and II diagnoses, 1,342 inpatient substance abusers completed the Revised NEO Personality Inventory (NEO-PI–R) and the Minnesota Multiphasic Personality Inventory—2 (MMPI–2) and were assessed with structured clinical interviews to determine diagnostic status. Results demonstrated that scores from the NEO-PI–R (a) were substantially related to the majority of diagnoses, accounting for between 8% and 26% of the variance in the diagnostic criteria; (b) explained an additional 3% to 8% of the variability beyond 28 selected MMPI–2 scale scores; (c) increased diagnostic classification an additional 7% to 23% beyond MMPI–2 scale scores; and (d) were significantly more useful when examined at the facet trait level than at the domain trait level. Implications for incorporating measures of normal personality into clinical assessment batteries are discussed. Assessment in clinical settings often relies on instruments such as the Minnesota Multiphasic Personality Inventory—2 (MMPI–2; Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989) designed to measure personality pathology and predict psychiatric diagnoses. In contrast to psychopathology scales designed to describe and predict clinical status, normal personality instruments provide dimensional measures of personality traits. The use of psychopathology inventories that focus on patterns of responses that deviate from the norm has strong support for predicting diagnoses and assisting in the development of treatment plans. In contrast, measures of normal personality rely on trait constructs to explain patterns of behavior that can be observed in all individuals, not just those common in psychopathological groups. Costa and McCrae (1992a) suggested that measures of normal personality traits such as those of the five-factor model (FFM)—neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness—may enrich the understanding of a patient’s psychological and interpersonal functioning, thereby improving anticipated symptom course and treatment response. Over the past decade, a growing body of literature has emerged that shows normal personality dimensions such as those in the FFM can be theoretically and empirically linked to measures of psychopathology, most notably those that assess personality disorders (PDs; Reynolds & Clark, 2001; Trull, Widiger, & Burr, 2001; Widiger & Costa, 2002). Given that scores on measures of normal personality are related to paper-and-pencil tests commonly used to assess psychopathology, a central question regarding the usefulness of normal personality trait measures in clinical settings is the degree to which they provide unique, clinically relevant information beyond that available from psychopathology scales (Ben-Porath & Waller, 1992). The addition of an inventory to any test battery used for psychiatric assessment represents an investment of time and money that must be carefully balanced against what is gained in terms of predicting relevant outcomes. Although the inclusion of redundant assessments might improve the overall reliability of diagnostic judgments, this might also be achieved by adding alternative measures of psychopathology. Thus, evidence of the incremental validity of measures of normal personality is important for evaluating when the benefits outweigh the costs in a particular assessment situation. The purpose of the current study was to examine the extent to which adding a measure of normal personality to an assessment battery that includes a psychopathology personality inventory facilitates prediction of psychiatric disorders. This was evaluated in a large sample of inpatient substance abusers who had been assessed through well-validated structured clinical interviews to determine diagnostic criteria related to Axis I and Axis II disorders. Participants completed the Revised NEO Personality Inventory (NEO-PI–R; Costa & McCrae, 1992b) and the MMPI–2 (Butcher et al., 1989). Because the interviews were conducted without knowledge of scores on the personality inventories, the resulting diagnoses provided an independent criterion for examining the incremental validity of a normal personality measure in the prediction of selected Axis I and II diagnoses.