Validating the Italian version of the Level of Personality Functioning Scale - Brief Form 2.0 (LPFS-BF 2.0): internal structure, temporal stability and construct validity.

Background: Contemporary models of personality assessment emphasize a dimensional rather than a categorical framework for measuring an individual's level of personality functioning. This viewpoint has also been incorporated into official diagnostic manuals, such as the Alternative DSM-5 Model for Personality Disorders (AMPD). Assessment instruments for personality functioning according to the AMPD are increasingly being developed and used, but controversies remain regarding the two-factor (vs. one-factor) structure and psychometric properties of such instruments in different countries.

Methods: To help fill these gaps in the literature, in this study we tested the internal structure, temporal stability, and construct validity of the Level of Personality Functioning Scale-Brief Form 2.0 (LPFS-BF 2.0), a convenient self-report screening questionnaire of the AMPD level of personality functioning, on a final sample of 482 non-clinical adults (369 females, 112 males, one non-binary; age range = 18-83, M = 34.6, SD = 16.4). Internal structure of the Italian LPFS-BF 2.0 was tested by Confirmatory Factor Analysis. Temporal stability and construct validity of the total score and of the Self and Interpersonal functioning subscale scores were tested using Pearson's correlations and Steiger's Test.

Results: A two-factor structure for the LPFS-BF 2.0 was supported, and correlation analyses provided convergent and discriminant validity evidence for the total and the two Self and Interpersonal subscale scores against external self-report measures of problematic self and interpersonal functioning, overall personality dysfunction, general psychological symptoms and lower quality of life. As such, the total score and the two Self and Interpersonal subscales yielded correlations with external criteria of medium to large effect sizes (i.e., Pearson's r), all significant at the p < .001 level. Finally, the present study provides the first empirical assessment of the LPFS-BF 2.0 temporal stability over an interval of 11.5 weeks, demonstrating a high temporal stability for both the total scale and the two subscales (rs above .70 for all three, ps < .001).

Conclusions: The Italian version of the LPFS-BF 2.0 yielded similar psychometric properties to the original scale and other international adaptations, suggesting its utility for personality assessment research and practice.