Facilitating clinical application of a dimensional model for personality disorders across the entire adult lifespan: thresholds for dysfunction and a multi-method approach.

Introduction: The classification of personality disorders (PDs) may be enhanced by dimensional models such as the Alternative Model for Personality Disorders (AMPD) and the ICD-11. However, their implementation in clinical practice remains limited, particularly among older adults, who are underrepresented in PD research. Given that personality pathology may vary across the lifespan, incorporating an age-sensitive perspective is essential when applying dimensional models. Methods: This study included a non-clinical sample of 754 participants aged 18 to 97 and a clinical sample of 102 older adult patients aged 65 and above. The discriminative validity of the LPFS-BF 2.0 and PID-5-BF + M was first assessed. Subsequently, age- and gender-specific normative thresholds were developed based on the non-clinical sample and evaluated within the clinical sample. Finally, self-report measures were compared with informant reports and clinical interview data (STiP-5.1) in the clinical older adult group. Results: Both the LPFS-BF 2.0 and PID-5-BF + M effectively differentiated between clinical and non-clinical participants. Age and gender influenced mean scores, supporting the need for adjusted normative thresholds. These thresholds successfully identified clinically elevated cases, particularly for the LPFS-BF 2.0 total score and the PID-5-BF + M domains of Negative Affectivity, Detachment, and Psychoticism. Moderate agreement was observed between self-reports, informant reports, and clinical interviews, although not all scales showed consistent correlations. Discussion: These findings highlight the importance of accounting for age and gender in the clinical application of dimensional PD models and support the use of multi-method assessment approaches.