Validation of the Polish Self and Interpersonal Functioning Scale (SIFS-PL) in community and clinical samples

The aim of this study was to examine the psychometric properties of the Polish version of the Self and Interpersonal Functioning Scale (SIFS-PL). The scale is designed to assess Criterion A of the DSM-5 Alternative Model of Personality Disorders (AMPD) - the four core elements of personality pathology (Identity, Self-direction, Empathy, and Intimacy) from the Level of Personality Functioning (LPF) for personality disorders (PDs).

Adult participants from 6 community and clinical samples (total N = 394; 83.2% female; age: M = 30.9, SD = 9.6) completed the SIFS-PL. A clinical subsample of 50 patients diagnosed with personality disorders additionally completed the Personality Inventory for DSM-5 (PID5).

Confirmatory factor analysis supported a bifactor four-factor model. All items had significant loadings on both the four specific elements and an overarching general personality pathology factor. The internal consistency ranged from acceptable to good for subscales and excellent for the global scale. In terms of criterion validity, results from the clinical subgroup were consistent with previous research on the SIFS. The SIFS-PL scales effectively discriminated between community sample participants and those suffering from depression, as well as an ambulatory clinical group with personality disorders.

Our findings underscore the robust psychometric properties of the Polish version of the SIFS, rendering it a promising tool for both screening and extensive research on personality disorders within contemporary dimensional models such as the AMPD and ICD-11. Its application in clinical settings can also be advocated. However, general scores and subscale scores might serve distinct purposes, warranting further investigation into their predictive validity.