Exploring the Temporal Dynamics of Interpersonal Variability and Personality Functioning at Within- and Between-Person Levels

Behavioral and affective instability in interpersonal interactions, a common struggle for many individuals with personality disorders, poses a significant challenge for clinicians and serves as a major obstacle preventing patients from making progress in their lives. This study examined the relationship between interpersonal variability and personality functioning using multilevel modeling (MLM), as well as the unique explanatory power of interpersonal variability beyond its mean level. This study employs a hybrid design that integrates a longitudinal approach with experience sampling features, collecting monthly data on significant interpersonal interactions from 342 adults over six months. Personality functioning was assessed with the Level of Personality Functioning Scale Self-Report (LPFS-SR), and interpersonal behaviors (submissive behavior, quarrelsome behavior, perceived other’s behavior) and interpersonal affects (positive and negative affect) were assessed with self-report measures. Results showed that variability in quarrelsome behavior, perceived other's behavior, and negative affect were significantly associated with personality functioning at both within-person and between-person levels. However, the relationships between variability in submissive behavior, positive affect, and personality functioning diverged at each level. Moreover, variability in submissive behavior and perceived other's behavior accounted for additional variance beyond mean levels. Overall, the results of this study suggest the importance of considering not only the degree but also the temporal variability of interpersonal behaviors and affects in constructing personalized models of personality pathology. Furthermore, they highlight the need to consider distinct results at within-person and between-person levels, with broader implications for clinical practice.