Latent Structure and Incremental Validity of the Semi-Structured Interview for Personality Functioning DSM-5 (STiP-5.1) in a Lithuanian Adolescent Sample.

As personality functioning has become central to contemporary conceptualizations of personality pathology, understanding its structure and optimal assessment has emerged as an important research priority, particularly in adolescence. This study examined the latent structure of the Semi-Structured Interview for Personality Functioning DSM-5 (STiP-5.1) and its incremental validity in predicting functional impairment beyond self-reported personality functioning. Participants were 178 adolescents aged 11-18 years, including a clinical sample (n = 104) and a community sample (n = 74). Confirmatory factor analyses (CFA) and bifactor modeling were used to evaluate the latent structure of the STiP-5.1. Hierarchical regression analyses examined whether clinician-rated personality functioning explained additional variance in functional impairment (WHODAS 2.0) beyond self-reported personality functioning assessed with the LoPF-Q 12-18 Short. The bifactor model demonstrated the best overall fit and supported the predominance of a strong general factor. Most reliable variance was attributable to this factor, whereas self- and interpersonal-specific factors contributed little unique variance. A four-factor CFA model also demonstrated excellent fit, supporting differentiation among identity, self-direction, empathy, and intimacy. Clinician-rated personality functioning explained additional variance in functional impairment beyond self-report measures. Self-functioning, particularly the element of self-direction, emerged as a unique predictor of functional impairment. Findings support a predominantly unidimensional conceptualization of personality functioning in adolescence while retaining clinically meaningful differentiation across LPFS domains and elements. The STiP-5.1 provides unique information beyond self-report assessment, supporting multimethod approaches to the assessment of personality functioning in adolescents.