To date, analytic approaches to parsing heterogeneity in BPD have utilized statistical methods that are suited to the identification of subgroups (e.g., LCA) or factors (e.g., EFA), but not to the comparison or combination of subtypes and factors. Markon and Krueger (2006)
demonstrated that person-centered and variable-centered analyses can be compared directly using the Bayesian Information Criterion (BIC, a parsimony-adjusted index of model fit), such that the model with the lowest BIC – whether continuous or categorical – best represents the latent structure of the data. Although this contribution provides useful leverage when deciding upon the latent structure of empirical data, the “true” nature of BPD may include continuous and discontinuous aspects. For example, individuals with BPD may vary dimensionally in terms of symptom severity, but the expression of the disorder may be qualitatively different in subpopulations (e.g., a more affectively dysregulated form versus a predominantly impulsive form). Such heterogeneity cannot be accommodated by conventional models; recent computational and statistical innovations, however, provide a new class of hybrid models that integrate categorical and continuous latent variables (Muthén, 2006
). In the current study, we used factor mixture modeling (FacMM), a hybrid latent variable model that combines CFA and LCA (Lubke & Muthén, 2005
), to probe the latent structure of the DSM BPD criteria.
The present study had two primary aims: 1) to resolve the latent structure of the DSM-IV BPD criteria using person-centered, variable-centered, and hybrid latent variable models; and 2) to explore additional, theoretically justified indicators of BPD among individuals with the phenotype with the intention of identifying qualitatively distinct subgroups. Our approach was divided into two phases that addressed the above aims in sequence. First, we compared latent variable models of the BPD diagnostic criteria in a large mixed clinical and community sample. In view of the evidence for one-factor models of BPD from previous CFA studies, we hypothesized that the best-fitting model for Phase 1 would be a factor mixture model that included a single latent factor (BPD severity), but more than one latent class. At a minimum, we expected at least two classes—a symptomatic class and an asymptomatic class (i.e., those who match the diagnostic prototype versus those who do not, respectively; Clifton & Pilkonis, 2007
In Phase 2 of our analyses, our aim was to differentiate among individuals with significant BPD symptomatology using four theoretically coherent variables—anger, aggressiveness, antisocial behavior, and mistrustfulness—that might have greater sensitivity to individual differences among persons with BPD than the DSM criteria alone. We selected these variables as potential differentiators among individuals with the BPD phenotype on the basis of Kernberg’s theory (Kernberg & Caligor, 2005
), as well as recent empirical data supporting the utility of these variables in identifying BPD subtypes (Lenzenweger et al., 2008
; Morse et al., 2009
). Briefly, Kernberg’s model of BPD (and more broadly, borderline personality organization [BPO]) distinguishes between individuals with high versus low levels of anger, where intense anger is a core motivational component of severe BPD. Further, among those characterized by high anger, there is a distinction between individuals who project their anger onto others in the form of interpersonal mistrustfulness versus those who direct anger toward others as interpersonal aggression and antisocial behavior. Of note, Kernberg’s (1975)
theory of BPO encompasses a wide range of constructs and conjectures, including the role of identity diffusion in BPD and the importance of primitive defenses in severe personality pathology. Our study focused specifically on anger and its manifestations as theoretically coherent variables that have considerable potential to differentiate among subtypes of BPD in empirical data.
We hypothesized that three subtypes would be mixed in our Phase 2 BPD-symptomatic sample: an angry aggressive/antisocial class, an angry mistrustful class, and a less severe class with low levels of anger, aggressiveness, and mistrustfulness. Phase 2 sought to parse heterogeneity within
the BPD phenotype, not among individuals who are largely asymptomatic (cf. Lenzenweger et al., 2008
). Drawing on our Phase 1 FacMM results, Phase 2 excluded individuals who were largely asymptomatic, while retaining a latent class of 100 individuals with syndromal levels of BPD symptomatology. To validate and characterize subtypes identified during Phase 2, we compared groups in terms of normal and abnormal personality, interpersonal problems, psychiatric impairment, and demographic factors. We anticipated that comparisons on these factors would provide convergent evidence for the validity of each subtype. For example, we predicted that external measures of aggression and disinhibition would be highest in the aggressive/antisocial class, whereas mistrustfulness would be highest and history of marriage would be lowest in the angry/mistrustful class.