Preadolescents' borderline personality features in a non‐Western urban context: Concurrent and longitudinal associations with physical and relational aggression,friendship exclusivity and peer victimization

The present study examined children's borderline personality features and their association with developmentally appropriate factors, including friendship exclusivity, forms of aggression and peer maltreatment with a non‐Western urban sample. The participants consisted of 234 Japanese preadolescents who were in the fourth and fifth grade (50% girls; ages: 9–11). Results of correlational analyses show that borderline personality features were stable during a six‐month period (r = 0.55). Moreover, results of mixed linear models indicate that friendship exclusivity was associated with elevated borderline personality features concurrently and longitudinally, after controlling for the effects of physical and relational aggression. Physical aggression (not relational aggression) and physical victimization (not relational victimization) also predicted relative increases in borderline personality features. These findings are discussed from a cultural‐developmental perspective.