Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 0 0 2026 09 07 1 12 EN Mehdi Rahmani Malek-Abad Department of Educational Psychology, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran. Mohammad Reza Abedi Department of Counseling, Faculty of Education and Psychology, University of Isfahan, Isfahan, Iran. 2026 02 21 2026 08 17 Objective: Establishing measurement invariance is essential to ensure that Minnesota Multiphasic Personality Inventory (MMPI-3) scores accurately reflect the intended latent traits and can be interpreted fairly across gender groups. Given the importance of measurement equivalence for valid clinical interpretation, this study evaluated Differential Item Functioning (DIF) and Differential Test Functioning (DTF) in the Personality Psychopathology Five (PSY-5) scales of the Persian version of the MMPI-3 within an Iranian clinical sample. Method: A total of 871 psychiatric outpatients (59% female; mean age = 28.76 ± 10.58) diagnosed with at least one DSM-5 disorder were recruited using convenience sampling. Invalid response protocols were excluded according to MMPI-3 validity criteria. Dimensionality of the PSY-5 scales was assessed via confirmatory factor analysis and Rasch measurement modeling, leading to the exclusion of the Disconstraint scale due to multidimensionality. Rasch-based analyses were used to evaluate item fit, reliability, local dependence (Q3), and DIF. Overall DTF was quantified using Signed and Unsigned Test Difference statistics, and Fisher’s Z tests were used to compare inter-scale correlation patterns across gender. Results: Significant DTF was observed for the four retained PSY-5 scales (Aggressiveness, Psychoticism, Negative Emotionality, and Introversion) following the exclusion of DISC due to multidimensionality. STDS values ranged from −0.27 to −0.37 and UTDS values ranged from 0.28 to 0.43, indicating consistent gender-related score differences of small-to-moderate magnitude at comparable latent trait levels that may influence clinical interpretation. Inter-scale correlations also differed across gender groups, particularly for PSYC, NEGE, and INTR, suggesting gender-related variation in scale functioning and construct associations. Conclusion: The findings indicate that several MMPI-3 PSY-5 scales may not demonstrate full measurement equivalence across genders in Iranian clinical populations. These results highlight the importance of local psychometric evaluation and careful interpretation of gender-based score comparisons when applying standardized personality assessment instruments in non-Western clinical settings. https://ijps.tums.ac.ir/index.php/ijps/article/view/4566 https://ijps.tums.ac.ir/index.php/ijps/article/download/4566/1354