Posttraumatic stress disorder (PTSD) is a prevalent and highly disturbing mental health condition that occurs in response to extremely distressing events during the lifetime. First, military personnel represent a high-risk population for the development of posttraumatic stress symptoms (PTSS) or the full-diagnostic spectrum of the disorder due to deployment- and combat-related stressors during their military career. Despite the existence of well established and efficacious psychotherapy treatments for PTSD, access to trauma-focused psychotherapy is limited and veterans in particular experience high barriers to accessing help from the mental health care system. A substantial proportion of affected veterans receive no or inadequate treatment, increasing the risk of secondary adverse mental and somatic health outcomes, reduced social and occupational functioning, and of the condition becoming chronic. Second, internet-based interventions (IBI), particularly internet-based cognitive behavioral therapies (iCBT), have been shown to be efficacious and widely accepted for the treatment of a range of psychiatric disorders, including PTSD. IBI can already be seen as playing a potentially important role in supplementing the landscape and provision of psychotherapeutic interventions, and this is set to grow further in the future. Indeed, IBI should be particularly beneficial for patients in rural areas with a restricted psychotherapy infrastructure, for patients with restricted mobility, and for patients who desire greater anonymity and more independence regarding the time and location of psychotherapy access. Third, the systematic and reliable assessment of objective indicators of symptom expression and symptom change is of increasing interest and relevance for psychotherapy research. This dissertation thesis aims at incorporating these three pillars in four studies: First, a diagnostic identification of PTSD in veterans of the German Armed Forces (GAF) according to the main diagnostic manuals the International Classification of Diseases and Related Health Problems (ICD) and the Diagnostic and Statistical Manual of Mental Disorders (DSM); second, a meta-analytical evaluation of the efficacy of IBI in PTSD; third, an assessment of patterns of visual attentional bias in (traumatized) veterans (with PTSS); and fourth, an exploration of the modifiability of attentional bias in veterans after receiving iCBT. STUDY 1 investigated the concordance of PTSD prevalence rates when transiting between the diagnostic criteria of the DSM-IV, DSM-5, ICD-10, and proposed ICD-11 in a sample of service members of the GAF. High levels of agreement emerged between the DSM-IV and the DSM-5, and between the DSM-5 and the proposed ICD-11. Prevalence rates were significantly higher according to the proposed ICD-11 compared to the ICD-10, mainly due to the deletion of the time criterion. STUDY 1 provides support for the identification of six ‘core’ PTSD symptoms according to the proposed ICD-11, presenting a high agreement rate with the set of twenty qualifiers according to the DSM-5. STUDY 2 provided meta-analytical evidence for the efficacy of IBI for the treatment of PTSD. Twenty randomized controlled trials (RCT) encompassing 21 comparisons were included, evaluating either iCBT or internet-based expressive writing (iEW) with passive or active control conditions. The results revealed that iCBT was more efficacious than passive control conditions at post-treatment assessment (0.66 ≤ g ≤ 0.83). No superiority of either iCBT or iEW was found in contrast to active control conditions. Subgroup analyses revealed no significant moderators of iCBT efficacy. More research is needed to prove the efficacy of IBI in contrast to active control treatments and further explore the impact of moderators on treatment efficacy. STUDY 3 measured patterns of attentional bias in GAF veterans with PTSS, traumatized veterans without PTSS, and unexposed healthy veterans. In a free-viewing task, participants were presented with pairs of combat-related and neutral pictures, of more general threat-related and neutral pictures, and of emotional and neutral faces, while their eye gazes were tracked. Further, the internal consistency of attentional bias indicators was calculated. The findings provide support for the maintenance hypothesis in PTSS. There was no robust evidence to support the hypothesis of hypervigilant behavior in PTSS. Findings on attentional bias variability remain unclear. Internal consistency varied across attentional bias indicators, highlighting the need for future research in this regard. STUDY 4 investigated the modifiability of attentional bias in veterans with PTSS through the provision of iCBT. In a free-viewing task, participants were presented with combat-related, general threat-related, and neutral pictures, and with faces with negative emotional valence and neutral facial expressions while their eye gazes were tracked. Attentional bias was examined pre- and post-intervention and at a three-month follow-up. No modifications in attentional bias were observable over time. Future investigations are warranted to systematically investigate objective measures of symptom expression and symptom change together with subjective symptom reporting and symptom change in response to psychotherapeutic treatment options. In summary, this dissertation thesis provides a threefold contribution to the current landscape of psychotherapy research: First, it supports the concordance between the DSM-5 and the ICD-11 diagnostic criteria for PTSD. Second, it proves the efficacy of IBI for PTSD. In view of the growing relevance of IBI as a supplement to psychotherapeutic care, future research needs to examine its long-term efficacy, whether it shows equal or superior efficacy compared to other active (control) treatments, potential side effects, and whether it may lead to a deterioration of symptoms. Moreover, studies should focus on tailoring IBI to the specific needs of different patient populations to ensure patients’ safety and satisfaction with IBI. Third, the present thesis underlines the need for systematic and reliable assessments of objective indicators of symptom presentation and of symptom change, in addition to subjective reports. Moreover, methodological approaches need to be extended to measure diverse dimensions of symptom presentation and symptom change and gain a better understanding of their interplay. A multidimensional diagnostic approach and treatment evaluation will be of key relevance for future intervention research and evidence-based practice.
