This study examined both mean levels and intraindividual variability in the mood and interpersonal behavior of individuals with borderline personality disorder (BPD) and nonclinical control participants over a 20-day event-contingent recording period. Individuals in the BPD group experienced more unpleasantly valenced affect and were less dominant, more submissive, more quarrelsome, and more extreme in overall levels of behavior than control participants. In addition to these mean-level differences, individuals with BPD also reported more intraindividual variability in overall affect valence and in pleasantly valenced affect; displayed greater variability in dominant, quarrelsome, and agreeable behaviors; and exhibited an increased tendency to "spin" among interpersonal behaviors relative to nonclinical control participants. The findings document behavioral and affective manifestations of BPD in the context of naturally occurring interpersonal situations.
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