**2.2 Interventions**

In the first two studies, treatment effects from two well-known psychological interventions were compared: Narrative Exposure Therapy or NET [27] and Present-Centered Therapy or PCT [28].

In NET, TF CBT is embedded in an autobiography, offering a lifespan time-frame for imaginal exposure. Following the introductory session, the therapist and patient collaboratively create a timeline of the patient's life; subsequently elaborating this timeline in the next sessions. The final session allows the patient to receive the documented narration and focus on the future. This short-term treatment approach, which can be disseminated among local para-professional staff, is considered an innovative modification of TF CBT for vulnerable populations in low-resource regions. NET was extensively investigated in various populations of refugees and displaced persons in war- and disaster-affected areas, but also refugees and asylum seekers living in Western countries, demonstrating medium to large effect sizes and low dropout rates [29]. Some of those trials had investigated non-refugees, such as former political prisoners in Romania [17] or Chinese earthquake survivors [30, 31]. The lifespan perspective of NET suggests that this intervention shows high suitability for the population targeted in this trial.

As for PCT, in a trauma-informed context, the focus is explicitly *not* on traumatic content, but on problem-solving of current stressors or maladaptive interactions [28]. This equally innovative approach was developed as a control condition, contrasting the exposure-based technique in TF CBT. PCT, however, appeared to be an efficacious and acceptable stand-alone treatment for PTSD [9]. Just as NET, PCT showed low

dropout rates [9]. Contrary to NET, PCT allows for systematically focusing on current problems associated with PTSD. Following the introductory session, psycho-education explaining the links between trauma and current distress is provided. The next sessions focus on relieving interpersonal and other current stressors. In homework assignments, patients select the relevant issues. Thus, a kind of self-help document is developed. The final session is dedicated to taking stock and looking forward.

#### **2.3 Design, assessments and methods of analysis**

The first two studies involved two conditions (NET vs. PCT) and three assessment timepoints (pre-treatment, post-treatment and at 4 months follow-up). Participants were randomly assigned to 11 sessions of NET or 11 sessions of PCT; each session covering 90 minutes.

In study 1 [24], the variables of interest were symptom severity and the symptom clusters (re-experience, avoidance and hyper-arousal) of PTSD (DSM-IV; [32]), using the well-validated Clinician-Administered PTSD Scale (CAPS; [33]). In addition to calculating group means, an individual clinically significant change [34] was rated.

In study 2, capturing the impact of PTSD in patients' daily life, exploratory analyses of self-reported symptoms and several measures of resilience were conducted [25]. This approach allowed patients to report self-reported distress from PTSD (using HTQ; [35]), depression symptoms (BDI-II; [36]), subjective general distress (BSI; [37]), self-efficacy [38], quality of life [39] and finally post-traumatic growth [40].

To enhance the external validity of this research project, inter-session intervals were adapted to patients' preferences and possibilities (weekly or once in 2 weeks). The resulting variation in treatment duration was addressed by advanced statistical analyses, using a (multilevel) piecewise mixed-effects growth model [41] to determine weekly change rates in the outcomes across time (therapy vs. follow-up) and conditions (NET- versus PCT-groups).

Finally, to explore post-traumatic cognitive processing during the treatment process, qualitative patient-reported outcomes were collected in study 3 [26]. This study consisted of the qualitative analysis of trauma narratives and individual interview responses in a subsample of four Dutch participants from the NET condition. All four participants reported multiple ACEs**.** Qualitative data analyses were conducted by using MAXQDA text software [42].

For all studies, methodological quality was addressed by trial registration, approval from the medical ethical committee (Leiden University), conducting a power analysis before starting the studies, randomization, blinding of assessors, protocol adherence, checks of treatment adherence and interrater reliability, and use of independent assessors.
