Evaluating Taxometric and Dimensional Structure in Self-Report Personality Disorder Scales

The argument over whether psychiatric disorders are taxa (i.e., categorical) or are part of a continuous dimension of normal personality functioning is not new. Within the last decade, however, there has been a forceful shift in personality disorder (PD) nosology toward a dimensional view. This coincides with the increasing popularity of the suite of factor analytic procedures. There are a number of false assumptions made about categorical models and factor analyses that may contribute to prematurely closing the metaphorical door on categorical PDs and PD phenomena. In the current study, taxometric analyses, which do not make a priori assumptions about the underlying quantitative structure, were used to examine PD constructs from two PD scale sets (the MMPI-2 PSY-5 [Harkness, McNulty, & Ben-Porath, 1995] and the MMPI-2 PD Spectra [Mulay et al., 2018]) on an outpatient sample (n = 1,030) to further assess for the presence of taxa. The PSY-5 and PD Spectra vary in their aims toward representing dimensional constructs; therefore, the theoretical aims of assessment were hypothesized to influence taxonic results. Results indicated the presence of taxa for the Dependent Spectra, Schizoid Spectra, Schizotypal Spectra, Somatizing Spectra, and PSY-5 NEGE. Dimensionality emerged for Paranoid Spectra and PSY-5 PSC. All other scales yielded ambiguous structures. Findings are discussed and compared to extant taxometric findings and dimensional models of PDs. Results provide support for some constructs highlighted in bifactor models of PDs but also suggest that these constructs are not continuous with normal personality functioning. Limitations and directions for future research are discussed.