Borderline Personality Disorder (BPD) is one of the most studied personality disorders and is associated with significant outcomes such as suicide. Although BPD is represented in DSM-5 as a categorical diagnosis, it may be better characterized dimensionally, such as using the five-factor model of general personality (FFM; Clark, 2007; O'Connor, 2005; Samuel & Widiger, 2004; Samuel & Widiger, 2008; Saulsman & Page, 2004; Lynam & Widiger, 2001). Mullins-Sweatt and colleagues (2012) developed a self-report measure, the Five Factor Borderline Inventory (FFBI) to assess BPD traits using eleven facets from the FFM that are highly related to BPD. Previous research suggests that informant-reports may increase the reliability and validity of assessments and provide additional information (Klonsky, Oltmanns, & Turkeheimer, 2002). The current study developed an informant measure of the FFBI, Five Factor Borderline Inventory- Other Report (FFBI-OR) and examined its convergent and discriminant validity compared to the FFBI, FFM, and traditional measure of PDs. Overall, the FFBI-OR demonstrated good convergent validity and moderate discriminant validity with the FFBI, FFM, and other traditional measures of PDs. Additionally, the current study explored the incremental validity of the FFBI-OR over the FFBI in predicting functional impairment. The FFBI-OR did not exhibit incremental validity over the FFBI in predicting functional impairment
