Interpersonal trust is the foundation of all healthy and stable relationships, and is one of the most heavily studied constructs in the social sciences and beyond. The extensive investigation of interpersonal trust in different contexts results in a great number of different conceptualizations as well as different study approaches. Despite this variety of approaches, there exists a lack of realistic and ecologically valid ways of measuring interpersonal trust. Apart from several questionnaires, so-called “trust games” have gained lots of attention in recent years as they have several important advantages and are the first experimental approach towards interpersonal trust. Although trust games have high ecological validity in the sense that real behavior can be observed and measured, the operationalization of trust over the exchange of monetary units seems to reflect only one facet (possibly even one of the less important facets) of interpersonal trust. This is especially true when thinking about trust deficits reported in a clinical context, for example by patients with Borderline Personality Disorder (BPD), and existing measures do not seem to capture the relevant facets of interpersonal trust. Besides the gap in measurement methods for interpersonal trust, not much is known about interpersonal trust behavior in patients with mental disorders. In patients with BPD, study results suggest alterations in interpersonal trust. However, concerning other mental disorders – and even with clear impairments in the interpersonal realm – research on interpersonal trust is almost non-existent. Furthermore, for patients with BPD, a more differentiated insight in alterations in interpersonal trust is needed, as well as an understanding of the possible origins of the apparent alterations in interpersonal trust. The current thesis aims to broaden our understanding of interpersonal trust in the context of mental disorders, with a special focus on patients with BPD. The premise for this was making an attempt to close the gap in measurement methods for interpersonal trust. Summary 4 In Paper I, a scenario-based self-report questionnaire for the assessment of interpersonal trust behavior with a focus on high ecological validity and realistic trust scenarios was developed. The main goal was to gain insight into everyday interpersonal trust behavior beyond the results of existing measures like trust games and questionnaires. The result was an 8 item questionnaire (Interpersonal trust scenario questionnaire – ITSQ), with two scales labeled “entrusting known people with material items” and “entrusting unknown people with one’s well-being”. In the second part of Paper I, interpersonal trust in patients with BPD, major depressive disorder (MDD), social anxiety disorder (SAD) and a non-clinical control group (CG) were assessed. Results indicated that patients with BPD displayed the lowest levels of interpersonal trust. More specifically, patients with BPD reported trust deficits only towards known people and when entrusting them with material items. In trusting unknown people and when entrusting them with their well-being, they did not report lower levels than the CG. Patients with MDD and SAD did not report lower levels of interpersonal trust behavior compared to the CG in any of the investigated facets of interpersonal trust. In Paper II, possible origins of current trust behavior in the form of trust experiences were explored. We were especially interested in the origins of current trust alterations reported by patients with BPD. For the investigation of trust experiences, autobiographical memories of trust from both patients with BPD and non-clinical controls were examined. Results indicated that patients with BPD primarily retrieved situations in which their trust was failed by family members or romantic partners. Non-clinical controls mostly retrieved situations in which they trusted their friends and which ended well (their trust was not failed). Besides this, results suggested that patients with BPD consider experiences with trust and mistrust as significantly more relevant for their current lives than non-clinical controls. In Paper III, another group of interest concerning alterations in interpersonal trust was addressed: patients with post-traumatic stress disorder (PTSD) after interpersonal Summary 5
traumatization. Former studies indicated that focusing on interpersonal trust during trauma therapy influences the outcome profoundly. PTSD is associated with distorted cognitions, or so-called “stuck-points”, about the self, the world and other people. The thematic content of these stuck-points, as well as associations to trauma-specific variables and PTSD symptom severity, were examined in adolescent survivors of interpersonal traumatization. Trust stuck- points were especially important, as they were the only things which predicted PTSD symptom severity. The empirical data from this thesis provides further evidence of alterations in interpersonal trust in patients with BPD. Besides this, more detailed information can be drawn from our results, as trust deficits were reported only in the facet “entrusting known people with material items” however not in the facet “entrusting unknown people with one’s well-being”. The results from Paper I correspond with Paper II on autobiographical memories, in which patients with BPD recalled mainly situations in which their trust was failed by family members and romantic partners. For patients with PTSD, our results also suggest alterations in interpersonal trust, which corresponds to results from former studies. Distorted cognitions of trust seem to influence PTSD symptom severity. Implications which can be drawn from our results are that interpersonal trust seems to be a topic of great relevance in the context of several mental disorders. Besides this, it should be treated as the multi-faceted construct it is both during therapy and in research. This is firstly to understand in which facets of interpersonal trust patients display deficits, and secondly to provide individually tailored treatment methods that specifically target the difficulties an individual displays.
