Investigating differential item functioning among borderline personality disorder diagnostic criteria and internalizing/externalizing domains based on sexual orientation

Borderline Personality Disorder (BPD) is more frequently diagnosed among sexual minority (SM) populations. SM populations also report higher levels of internalizing and externalizing psychopathology, two core domains of clinical problems that are highly comorbid with BPD. Contextual factors (e.g., group-specific norms) might affect endorsement of BPD items for reasons other than an underlying liability to experience BPD, internalizing or externalizing psychopathology. Therefore, BPD items may be ‘easier’ to endorse (i.e., be associated with lower indicator thresholds) for SM populations relative to non-SM populations. We tested this hypothesis in a large, nationally representative sample of the US population (N=35,723, SM n=1,150) using an item response theory approach. Several BPD indicators demonstrated differential item functioning of indicator thresholds, though these results varied based on impairment and sex. Endorsement of impulsive sex and chronic suicidality were consistently associated with lower indicator thresholds among SM groups; lower BPD, internalizing and externalizing factor levels were necessary for item endorsement for SM individuals. Chronic suicidality and impulsivity criteria may conflate BPD-related variance with SM-specific factors, potentially non-pathological SM group norms, and minority stress processes. Implications for equitable diagnosis and future research on the BPD syndrome in SM populations are discussed.