The investigators will conduct a pilot RCT to test the preliminary efficacy of the Program for Alleviating and Resolving Trauma and Stress (PARTS) compared with a Nature-Based Stress Reduction for Trauma Survivors (NBSR-T) control group at reducing PTSD symptom severity measured by Clinician-Administered PTSD Scale (CAPS-5).~Secondary clinical outcomes include the effects of the intervention on self-reported PTSD symptoms (PCL-5; CAT-PTSD), disassociation (MDI), and disturbances of self-organization (ITQ). Secondary mechanistic outcomes include emotion regulation (DERS), self-compassion (SCS-SF), and decentering (EQ-D) .~Exploratory aims of the study are to investigate the effects on depression (CAT-DI), mental health (CAT-MH scales), self-trauma fusion (PRISM-D), perceived stress (PSS), internalized stigma (ISMI), and interoception (MAIA-2). Additional exploratory outcomes include changes in outcome variables among PTSD subjects with baseline DSO and those without DSO as defined by the International Trauma Questionnaire (ITQ).
This pilot RCT will test the preliminary efficacy of an intensive group model of Internal Family Systems (IFS) called the Program for Alleviating and Resolving Trauma and Stress (PARTS) compared with a Nature-Based Stress Reduction for Trauma Survivors (NBSR-T) attention placebo control group at reducing PTSD symptom severity measured by Clinician-Administered PTSD Scale (CAPS-5). In addition, the effects of the interventions on self-reported PTSD symptoms, disassociation, and disturbances of self-organization (DSO), as well as mechanisms of emotion regulation, decentering and self-compassion will be secondary outcomes.