Assessing Maladaptive Personality Traits in Individuals with Mild Intellectual Disabilities or Borderline Intellectual Functioning: Evaluating the Validity of the PID-5-IRF-SF

Objectives Diagnosing personality pathology in individuals with Mild Intellectual Disability (MID) or Borderline Intellectual Functioning (BIF) is challenging due to the risk of diagnostic overshadowing, whereby maladaptive personality traits may be misattributed to limitations in intellectual functioning. The Alternative Model for Personality Disorders (AMPD) offers a dimensional framework that may help address this risk. This study evaluated the validity of the Personality Inventory for DSM-5 Informant Report Short Form (PID-5-IRF-SF) in individuals with MID or BIF by examining its discriminant validity with respect to Total Intelligence Quotient (IQ) and its convergent validity with an established informant-based assessment. Methods Forty-three adults with MID or BIF (mean IQ = 68) were recruited from specialized outpatient services. Informants completed the PID-5-IRF-SF and the Standardized Assessment of Personality (SAP). Discriminant validity was examined using linear regression analyses with IQ as the predictor. Convergent validity was assessed using Pearson correlations between PID-5-IRF-SF and SAP total scores. Results IQ accounted for a negligible and non-significant proportion of variance in PID-5-IRF-SF scores. IQ was not meaningfully associated with maladaptive personality trait severity. A moderate positive correlation was observed between PID-5-IRF-SF and SAP total scores, supporting convergent validity. Conclusions The findings provide preliminary support for the validity of the PID-5-IRF-SF for assessing maladaptive personality traits in individuals with MID or BIF, with minimal influence of IQ within this range. Informant-based dimensional trait assessment may help reduce diagnostic overshadowing, while careful clinical interpretation remains essential.