Treatment dropout is a primary challenge for individuals suffering with posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD) following trauma exposure. Treatments for PTSD+AUD are effective at reducing symptoms, yet treatment attrition is a critical issue. Dropout rates among individuals with PTSD+AUD are higher than for those with PTSD alone, and dropout is associated with less clinical improvement. A clearer understanding of the factors that contribute to dropout, including those who initiate services but do not start treatment (nonstarters) and those who start but do not complete treatment (noncompleters), will enable us to develop strategies that improve retention and treatment outcomes for this population. Examining modifiable and theoretically informed constructs, such as difficulty tolerating emotional distress and coping motives for alcohol use, may improve our understanding of treatment dropout. Additionally, observer ratings of in-session behavior, or “thin slice” ratings, is a method of measuring predictors more proximal to when dropout occurs and has the potential to be a robust predictor of dropout. Thin slice refers to short (e.g. 30 second) video clips of expressive behavior rated by trained observers on specified constructs or outcomes of interest. The proposed F32 will use mixed methods to explore reasons for treatment dropout using data collected from an existing clinical trial for women with PTSD and heavy drinking following sexual assault. Specific aims are: 1) To identify themes related to reasons for dropout for nonstarters and noncompleters by conducting qualitative interviews with providers of sexual assault services (N = 10), which will be used to develop the “thin slice” rating constructs of observed participant behavior for use in Aim 2. 2) To predict dropout and related treatment processes (N = 100) using thin slice ratings and advanced statistical methods. Treatment dropout will be examined within each treatment condition (imaginal exposure and alcohol skills training) and between treatment conditions to test whether certain thin slice constructs are better at predicting dropout for certain types of treatment. We will also examine trajectories of treatment processes related to dropout: difficulty tolerating emotions and alcohol craving. 3) To enrich and contextualize Aim 2 quantitative findings by concurrently conducting qualitative interviews exploring treatment initiation and dropout with women enrolled in a clinical trial for PTSD and heavy drinking following sexual assault (N = 25). The applicant will receive training in 1) PTSD and alcohol treatment process research, 2) conducting studies predicting dropout in clinical trials, 3) skill development for collecting and analyzing qualitative and quantitative data, and 4) manuscript and grant writing. The proposed study will make substantial contributions to our understanding of dropout, a necessary first step to the development of strategies to increas...