ABSTRACT
Jumping to Conclusions (JTC) and Bias Against Disconfirmatory Evidence (BADE) are interrelated cognitive biases implicated in psychosis. Individuals diagnosed with Borderline Personality Disorder (BPD) may experience psychotic symptoms, raising the question of whether they also exhibit these biases. However, research investigating the presence of these biases in individuals with BPD remains limited. Existing studies are marked by significant methodological shortcomings, including overreliance on self-report measures and the lack of clinical comparison groups. The present study examined JTC and BADE, using both objective and self-report measures, in individuals with BPD (N = 20), healthy controls (N = 20), and individuals with schizophrenia (N = 20). A serial disambiguation task and a multi-trial beads task were utilized as objective measures of BADE and JTC, respectively, while the Davos Assessment of Cognitive Biases Scale (DACOBS) served as the self-report measure. On the disambiguation task, individuals with BPD showed greater BADE than healthy controls but less than those with schizophrenia. On the beads task, 90% of the schizophrenia group and 65% of the BPD group exhibited JTC bias, compared to only 5% of the control group. There were no significant differences between the two clinical groups on JTC and draws to a decision. On the DACOBS, the BPD group reflected higher levels of belief inflexibility (a self-report index related to BADE) than healthy controls, but lower than those with schizophrenia. In contrast, on the jumping to conclusions scale, the BPD group did not differ from either the schizophrenia or the healthy control groups. Scores on self-report and objective measures did not correlate overall.